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Salt-tolerance of fresh-water fish groups in relation to zoogeographical problems
... Most aquatic organisms can only tolerate a specific salinity range [106] .The physiological adaption of each species is determined by the salinity of its surrounding environment. Most species of fish are stenohaline, or exclusively freshwater or exclusively saltwater [109]. However, there are a few organisms that can adapt to a range of salinities. ...
... Anadromous organisms live in saltwater but spawn in freshwater. Catadromous species are the oppositethey live in freshwater and migrate to saltwater to spawn [109]. True euryhaline species can be found in saltwater or freshwater at any point in their life cycle [109]. ...
... Catadromous species are the oppositethey live in freshwater and migrate to saltwater to spawn [109]. True euryhaline species can be found in saltwater or freshwater at any point in their life cycle [109]. Estuarine organisms are true euryhaline. ...
Water desalination plants produce huge amounts of reject brine, which are usually sent back to the sea, where they could, in the long run, result in detrimental effects on the aquatic life as well as the quality of the seawater in the area.
The major goal of this study is to investigate the effect of brine disposal of Deir El- Balah desalination plant on the quality of seawater.
The negative impact relatively features with high temperature, high salinity and low dissolved oxygen in water.
This study was conducted on the status-quo of Deir El-Balah desalination plant.
The capacity of Deir El-Balah desalination plant today is around 2600 m3/d with a recovery rate of 42%.
It depends in water desalination whether on the saline well that was drilled in the plant or the beach wells.
The study focused on figuring out the characteristics of the seawater in its natural status without the effect of brine by considering a reference point (R) which is 1600 m away from the south of the disposal point.
In addition, the characteristics of the seawater in the discharge area after the Brine discharge were studied and the difference in the measured parameters refering to the reference point R was observed.
It is noteworthy that the study was through two seasons of the year, summer and autumn and the process of sampling was done in three rounds in total of thirty points distributed within an area of 200 m2 surrounding the brine disposal point.
Seawater parameters that are the most important in this issue, salinity (measured by EC), temperature, dissolved oxygen (DO), turbidity and pH were measured according to the previous studies due to its effect on the seawater quality and the marine life.
After the analysis of the above-mentioned parameters, the study explained that brine of Deir El-Balah desalination plant has no effect on the seawater quality, since the maximum values from the three rounds measurement of EC, temperature, DO, Turbidity, and pH are 60.2 mS/ cm, 29.4 Co, 9.2 mg/l, 5.36 NTU, 8.349 respectively.
This may be due to the small volume of the brine quantity that is resulted from the desalination process which is considered relatively little to influence the seawater and represents nothing comparing with the physical and chemical continuous changes in the seawater.
The study has recommended that all environment interested authorities as environment quality authority and other responsible institutions should conduct monitoring and evaluation programs for large scale desalination plant and using modeling to simulate reality precisely throughout the year, in order to know the best options to build desalination stations that neither affects the seawater quality nor causes negative effect on the sea environment.
... A classic question related to the distribution of fishes, especially those considered stenohaline freshwater, is how some species have dispersed over long geographic ranges when their only route from one freshwater river system to the next seems to require passage via the ocean. Myers (1949) stated how it might have been possible for some fish to swim through narrow sea barriers for short period of time. This would require at least a short-term tolerance of seawater, enough to allow them to swim from one river system to the next. ...
... Fish within the family, Poeciliidae can be found in freshwater or brackish water based on geographical distribution (Myers, 1949;Myers, 1976;Lucinda, 2003;Matamoros, 2014). The family consists of 299 species and can range in size from 13.9 mm up to 200 mm (Lucinda, 2003). ...
... Because the family, Poeciliidae consists of stenohaline and euryhaline fish, their geographic distribution has been studied as to how different species tolerate different salinity ranges and how they may have been distributed around the world. Myers (1949) classifies the family, Poeciliidae, as secondary freshwater fish. Meaning, they are salt-tolerant but considered freshwater fishes. ...
... Las especies se han diferenciado también según el hábitat que ocupan (Myers, 1949), como primarias cuando son estrictamente de agua dulce o secundarias cuando habitan mayoritariamente estuarios. Este estudio toma en cuenta esta diferencia, ya que pueden presentarse grandes variaciones en la presencia de especies secundarias en el río, debido a que toleran la salinidad, lo cual les permite migrar hacia el mar, no así para las especies primarias. ...
... Finalmente, se realizó un análisis de correspondencia canónica para establecer la relación entre la abundancia relativa de las especies en cada zona y sus parámetros ambientales. Con el fin de entender la posible interacción entre estos parámetros y la composición de especies, se consideraron solamente las 11 especies de peces primarios (exclusivos de agua dulce, Myers, 1949), ya que son los únicos que no pueden abandonar este hábitat, a diferencia de las especies secundarias (que habitan mayoritariamente estuarios, Myers, 1949) que podrían ingresar en el mar y eventualmente penetrar en otros ríos. ...
... Finalmente, se realizó un análisis de correspondencia canónica para establecer la relación entre la abundancia relativa de las especies en cada zona y sus parámetros ambientales. Con el fin de entender la posible interacción entre estos parámetros y la composición de especies, se consideraron solamente las 11 especies de peces primarios (exclusivos de agua dulce, Myers, 1949), ya que son los únicos que no pueden abandonar este hábitat, a diferencia de las especies secundarias (que habitan mayoritariamente estuarios, Myers, 1949) que podrían ingresar en el mar y eventualmente penetrar en otros ríos. ...
La interpretación de la diversidad biológica puede resultar muy compleja, ya que existe una dinámica basada en el origen y en la diversificación de las especies, así como en los efectos antrópicos, tales como la introducción de especies invasoras, cuya consecuencia puede conducir a la extinción local de especies nativas. El objetivo de este trabajo fue analizar la variación temporal (2012 y 2017), tanto en composición como en distribución de la ictiofauna a lo largo del río Atacames, noroccidente del Ecuador. En 2012 se registró: 1) la presencia de Astyanax ruberrimus que se extinguió localmente para el 2017; y 2) la presencia de la tilapia (Orechromis niloticus) como única especie introducida a la que se sumó el guppy (Poecilia gillii) para el 2017. Adicionalmente, el aumento en las actividades humanas condujo a un arreglo en la diversidad, abundancia y distribución de peces a lo largo del cauce, lo que determinó además que algunas especies se dispersaran hacia la zona alta de la cuenca.
... Freshwater fishes are an exemplar for exploring concepts in ecology, evolution and biogeography, as their distributions are naturally confined to the dendritic arrangement of river drainage basins (Berra, 2001). Eighty years ago, the American ichthyologist George S. Myers proposed a classification of inland fishes according to the presumed salinity tolerance and eco-evolutionary history of species (Myers, 1938(Myers, , 1949. This classification continues to be widely used by ichthyologists and when exploring patterns and drivers of fish biogeography (Cano-Barbacil, Radinger, Grenouillet, & García-Berthou, 2022;Filipe et al., 2009;Smith & Bermingham, 2005). ...
... Myers, little empirical information on salinity tolerance of fish was available. Myers based his classification on frequent observations of secondary species in coastal habitats or in hyperhaline waters, or the fact that they had been able to cross the sea and reach islands such as Madagascar, the Seychelles, or the West Indies, in contrast to primary species (Myers, 1949). Recent reviews of existing experimental studies have demonstrated that in general, primary species such as cyprinids, characids and most siluriforms demonstrate lower salinity tolerance compared with secondary and peripheral species Seale et al., 2024). ...
Eighty years ago, George S. Myers classified inland fishes in three divisions (primary, secondary and peripheral) based on their salinity tolerance and eco‐evolutionary history. Although this classification has been followed by many fish studies, it has also received considerable criticism. Here, we aim to test for differences in salinity and thermal tolerance, species traits and distribution patterns among the three divisions using data for about 21,000 species. We found that primary fishes have much less salinity tolerance than secondary and peripheral species, with some secondary fishes displaying the highest tolerances (>100 ppt). We also provide, for the first time, evidence of significant phylogenetic signal of salinity tolerance, comparable in magnitude to conservative traits, and show that studied peripheral and secondary species have maintained or even developed salinity tolerance, in contrast to primary fishes. Although peripheral fishes are the most different, and despite the large variability observed within some families, primary and secondary species also show differences in morphology and life‐history traits. The distribution ranges and genetic diversity of primary and secondary fish divisions are similar and differ from peripheral species, suggesting that although there is evidence of oceanic dispersal of a few secondary fishes at evolutionary time scales, it is a rare contemporary phenomenon. Importantly, a few findings outlined in this study, namely, differences in salinity tolerance, rely on limited data. Thus, we urge for additional empirical research on the salinity tolerance of freshwater fish, which remains largely unexplored, to help clarify differences among and within clades.
... Salmoniformes). These orders have a high salinity tolerance and dispersal ability [67,68] that favour dispersal between river basins, allowing them to colonize regions inaccessible for strict freshwater fishes after glacial events [69]. Thus, the dispersal capacities of marine-derived fishes could have allowed them to diversify at mid-latitudes and temperate regions (e.g. ...
... Thus, the dispersal capacities of marine-derived fishes could have allowed them to diversify at mid-latitudes and temperate regions (e.g. Atheriniformes and Beloniformes), explaining their distribution, species richness and LDGs [23,68]. For instance, regions such as the Australasia realm are dominated by marine-derived clades belonging to the Galaxiformes and Atheriniformes orders, a pattern explained by its long spatial and temporal isolation that prevented the colonization of primary freshwater clades [70]. ...
Tropical lands harbour the highest number of species, resulting in the ubiquitous latitudinal diversity gradient (LDG). However, exceptions to this pattern have been observed in some taxa, explained by the interaction between the evolutionary histories and environmental factors that constrain species' physiological and ecological requirements. Here, we applied a deconstruction approach to map the detailed species richness patterns of Actinopterygian freshwater fishes at the class and order levels and to disentangle their drivers using geographical ranges and a phylogeny, comprising 77% (12 557) of all described species. We jointly evaluated seven evolutionary and ecological hypotheses posited to explain the LDG: diversification rate, time for speciation, species–area relationship, environmental heterogeneity, energy, temperature seasonality and past temperature stability. We found distinct diversity gradients across orders, including expected, bimodal and inverse LDGs. Despite these differences, the positive effect of evolutionary time explained patterns for all orders, where species-rich regions are inhabited by older species compared to species-poor regions. Overall, the LDG of each order has been shaped by a unique combination of factors, highlighting the importance of performing a joint evaluation of evolutionary, historical and ecological factors at different taxonomic levels to reach a comprehensive understanding on the causes driving global species richness patterns.
... Equatorial freshwater fish are highly diverse and not easily characterized by any specific features. Scientists distinguish freshwater fish into three major groups in terms of saltwater tolerance and the presumed ability to spread by overcoming maritime barriers: [4] fish that are strictly intolerant of saltwater (primary division), rarely capable of crossing narrow marine boundaries (secondary division), and representatives of marine families colonizing inland water from the sea (peripheral division). Fish ...
... Endemic species were identified based on their distribution restricted to haor basins in Sylhet [12]. In addition, identified fish were categorized into four groups based on respondent perceptions, namely, abundantly available (AA): available in abundance all year round (frequency of occurrence: 76-100%), commonly available (CA): usually found in small numbers all year round (frequency of occurrence: 51-75%), moderately available (MA): rarely found in the study area (frequency of occurrence: 26-50%), and rarely available (RA): found infrequently in very small numbers (frequency of occurrence: 1-25%) [4,25]. The conservation status of each species was listed in accordance with the IUCN Red List of Bangladesh [10] and Threatened Species of Global Red List [16]. ...
Biodiversity assessment is important for evaluating community conservation status. The
haor basin in Sylhet Division represents a transitional zone with high species availability, rare occurrences and endemism. As a result, this study aims to describe the haor-based freshwater fish composition, including habitat, trophic ecology, availability and conservation status. Semi-structured questionnaires were used to collect data on fish samples through focus group discussions, field surveys, and interviews with fisheries stakeholders on a monthly basis. We identified 188 morphospecies, of which 176 were finfish and 12 shellfish, distributed into 15 orders and 42 families where 29%, 42%, 15%, and 14% species were commonly available, moderately available, abundantly available, and rarely available, respectively. Cypriniformes was the dominant order in both total species and small indigenous species identified. Approximately 45.34% of species were riverine, 31.58% floodplain residents, 12.55% estuarine, 2.83% migratory, and 7.69% were exclusively hill stream residents. Carnivores and omnivores were the most dominant trophic groups. A total of 87.76% species were used as food, 12.23% as ornamental and 6.91% as sport fish. Approximately 50 species were threatened (7 critically endangered, 23 endangered and 20 vulnerable) at the national level, most of them belonging to Cypriniformes and Siluriformes. Based on endemism, 16 species were endemic
of which Sygnathidae, Cobitidae, Olyridae, Cyprinidae and Balitoridae fell under the threatened category. Minimizing intense fishing efforts, banning indiscriminate fishing and destructive fishing gear, initiating fish sanctuaries and beel nurseries, and implementing eco-friendly modern fishing technology are suggested to conserve the threatened species. This study represents a guideline for assessing the availability and conservation of freshwater fish in the Sylhet belt and serves as a reference for decision-makers in order to allow for the sustainable exploitation of fisheries resources
within an ecosystem-based framework.
... In the Figure 1, numbers represented sampled localities and letters represented collections events (i.e., museum records) with material deposited at the UCR; the associate data are provided in Tables 1 and 2, respectively. The tolerance to salinity by family is listed according to the classification by Myers (1949). Taxonomic nomenclature followed Fricke et al. (2019). ...
... Based on salinity tolerances (sensu Myers 1949), the majority of the species recorded were peripheral (27 species, 44.3%), followed by secondary freshwater fishes (20 species, 32.8%). Eight families (Bryconidae, Characidae, Curimatidae, Erythrinidae, Heptapteridae, Lebiasinidae, Loricariidae and Trichomycteridae) and 14 species (23.0% of the total fish diversity) of primary freshwater fishes were recorded (Table 3). ...
A checklist of the fishes of the Coto River basin, southern Pacific, Costa Rica, compiled from field and museum surveys is presented. A total of 61 species, representing 48 genera, 26 families and 11 orders are listed. Peripheral species were dominant (44.3%), whereas secondary and primary freshwater species represented 32.8% and 23.9% of the total diversity. The orders Cyprinodontiformes (12 spp.) and Perciformes (11) and the families Poeciliidae (8) and Cichlidae (7) were the most diverse. Two species (Lutjanus guttatus and Polydactylus approximans) were new records for Costa Rican freshwaters and ten additional species were found to have expanded geographical ranges. An identification key and a complete photographic album of all fish species recorded are presented. This investigation provides a framework for future studies on fishes from this area complementing previous efforts seeking to increase our knowledge about the freshwater ichthyofauna of the central and southern Pacific regions of Costa Rica.
... La comunidad de peces del corredor fluvial del río Tuira se compone principalmente de especies periféricas y secundarias que se distribuyen en un gradiente de salinidad generado por las mareas (Breder, 1927;Myers, 1949), las especies periféricas que más aportaron a diferenciar esta comunidad fueron Mugil curema, Centropomus unionensis, Cynoscion albus, Anchoa spinifer y Cathorops tuyra, todas asociadas a aguas salobres, no obstante, las especies primarias Ageneiosus pardalis, Sternopygus aequilabiatus y Brycon argenteus fueron las que mayor contribución en términos de fidelidad y especificidad al hábitat del corredor fluvial. ...
Introducción: La Laguna de Matusagaratí es un ecosistema con diversos hábitats y condiciones ambientales que determinan la diversidad y distribución de la vida acuática. A pesar de la conectividad hidráulica, los hábitats acuáticos generados por esta diversidad de condiciones ambientales podrían determinar la composición y estructura de los ensambles ícticos. Objetivo: Entender la estructura de la comunidad de peces en tres de estos hábitats. Métodos: Se realizó un muestreo multihábitat entre marzo 2022 y septiembre 2023, abarcando periodos de estiaje e inundación, en 29 sitios, usando distintas técnicas de pesca. Resultados: Se recolectaron 1 913 peces de 50 especies y 27 familias en aproximadamente 320 km². Se identificaron tres ensambles de peces, cada uno asociado a un hábitat específico. El corredor fluvial del río Tuira tuvo la mayor diversidad, seguido de los riachuelos y las lagunas temporales. Conclusiones: El análisis reveló diferencias notables entre estos hábitats, con el corredor fluvial dominado por especies periféricas, mientras que las lagunas presentaron una baja diversidad con especies generalistas o adaptadas a condiciones de hipoxia. La presencia de especies como Hoplosternum punctatum, Ageneiosus pardalis y Pimelodus punctatus en el humedal, evidencia la influencia del Chocó en la ictiofauna de Panamá. Estos hallazgos podrían tener implicaciones importantes para la formulación de estrategias de conservación del humedal.
... Species such as P. vivipara and O. niloticus are among those with the highest biomass representation in the assemblage. These species are typically freshwater, but since they originate from evolutionary lineages that were originally marine, they are classified as physiologically secondary or peripheral and can tolerate moderate salinity levels (Myers 1949;Franco et al. 2024). In addition to their freshwater affinity, these species also possess adaptations for surviving in hypoxic conditions. ...
Estuarine ecosystems exhibit substantial spatiotemporal variation in their environmental conditions, resulting in a dynamic fish assemblage. However, anthropogenic alterations in hydrological flow and nutrient concentrations can potentially modify the spatial and temporal structuring of the fish community. This study aimed to elucidate how the characteristics of fish assemblages vary in space and time in an estuary (Cocó River, Ceará State, Northeast Brazil) that experiences significant impacts stemming from untreated domestic effluent discharge and water transfer from other hydrographic basins. The fish assemblage exhibited low total species richness alongside a high number and biomass of freshwater species, including non-natives. A stable spatial structure across seasons was discerned, implying diminished connectivity between estuarine zones. Changes in the trophic structure of the ecosystem could be inferred from variations in trophic composition among different zones. The findings presented herein demonstrate the alterations that interbasin water transfer may induce in estuarine fish assemblages, with potential ramifications for ecosystem functioning.
... La dispersione avviene, però, nei corsi d'acqua con maggiori difficoltà (Compte & Olden, 2018) e con modalità peculiari rispetto agli ambienti terrestri, a causa della natura dendritica del reticolo idrografico, per la presenza della corrente e per l'isolamento che limita gli spostamenti dei pesci all'interno del proprio bacino imbrifero (McFadden et al., 2022). Nelle specie ittiche primarie (Myers, 1949) e primario-simili, infatti, il mare rappresenta una barriera invalicabile e, anche se i Salmonidi non rientrano in queste categorie, attualmente il Mediterraneo è troppo caldo e salato per poter essere utilizzato come mezzo per la propria dispersione (Lobon-Cervia et al., 2019). Nella fauna ittica, quindi, gli spostamenti conseguenti all'innalzamento termico dovuto ai cambiamenti climatici avverranno privilegiando l'asse longitudinale, ma tali movimenti verso monte potrebbero essere impediti dall'assenza di condizioni idonee in grado di permetterli. ...
La trota mediterranea, inserita nell’allegato II della Direttiva Habitat 92/43/CEE, è una specie fondamentale per gli ecosistemi acquatici dei corsi d’acqua appenninici, montani insulari e collinari per il suo ruolo al vertice delle reti trofiche.
La specie è minacciata da molteplici pressioni antropiche, tra cui le cospicue immissioni di trote alloctone, le captazioni idriche, le alterazioni e il degrado degli habitat fluviali ed i cambiamenti climatici. Le azioni di conservazione volte alla tutela di questa specie e del suo habitat sono di prioritaria importanza anche in virtù del generale contributo che apportano al ripristino o al mantenimento della funzionalità e della qualità degli ecosistemi fluviali, in linea con le Strategie Europea e Nazionale per la Biodiversità al 2030 e con il Regolamento sul Ripristino della Natura. Le linee guida, definite nell’ambito del progetto LIFE STREAMS (LIFE18 NAT/IT/000931) “Salmo ceTtii REcovery Actions in Mediterranean Streams”, sono rivolte agli enti gestori delle aree protette e dei Siti Natura 2000, alle Regioni e alle Autorità di Distretto Idrografico e contengono anche indicazioni per l’integrazione degli strumenti di pianificazione e di gestione previsti dalla direttiva Habitat e dalla Direttiva Quadro Acque.
https://www.isprambiente.gov.it/files2024/pubblicazioni/manuali-e-linee-guida/linee-guida_trota-mediterranea-mlg-20724.pdf
... Exposure to high salinities in L. perugiae has been shown to decrease metabolic rate [25], increase the production of Na + /K + -ATPase and oxidative phosphorylation proteins in the gills [23], and reduce adult body size [23]. Though predominantly associated with freshwater habitats, many fishes in the family Poeciliidae are able to tolerate a broad range of salinities, a factor potentially responsible for facilitating their dispersal across a wide geographic range [26][27][28][29]. While the mechanisms and consequences of salinity tolerance at the biochemical and physiological levels have been a focus of research in poeciliids [23,[30][31][32][33], the genetic and regulatory underpinnings of salinity tolerance have yet to be investigated in this family. ...
Salinity gradients act as strong environmental barriers that limit the distribution of aquatic organisms. Changes in gene expression associated with transitions between freshwater and saltwater environments can provide insights into organismal responses to variation in salinity. We used RNA-sequencing (RNA-seq) to investigate genome-wide variation in gene expression between a hypersaline population and a freshwater population of the livebearing fish species Limia perugiae (Poeciliidae). Our analyses of gill gene expression revealed potential molecular mechanisms underlying salinity tolerance in this species, including the enrichment of genes involved in ion transport, maintenance of chemical homeostasis, and cell signaling in the hypersaline population. We also found differences in gene expression patterns associated with cell-cycle and protein-folding processes between the hypersaline and freshwater L. perugiae. Bidirectional freshwater-saltwater transitions have occurred repeatedly during the diversification of fishes, allowing for broad-scale examination of repeatable patterns in evolution. Therefore, we compared transcriptomic variation in L. perugiae with other teleosts that have made freshwater-saltwater transitions to test for convergence in gene expression. Among the four distantly related population pairs from high- and low-salinity environments that we included in our analysis, we found only ten shared differentially expressed genes, indicating little evidence for convergence. However, we found that differentially expressed genes shared among three or more lineages were functionally enriched for ion transport and immune functioning. Overall, our results—in conjunction with other recent studies—suggest that different genes are involved in salinity transitions across disparate lineages of teleost fishes.
... Sulawesi is the largest island of the Wallacea, the transition zone between the continental Asian and Australian faunal regions (Doorenweerd et al., 2020;Myers et al., 2000;von Rintelen et al., 2012von Rintelen et al., , 2014. Isolation and the complex geological history explain the natural absence of primary freshwater fishes (sensu Darlington Jr., 1957fishes with little salt tolerance, an ecological concept; Lévêque et al., 2007;Myers, 1949; see Berra, 2007 for discussion) from the tropical island (Kottelat et al., 1993). Sulawesi's freshwater biota are best known for the adaptive radiations endemic to the island's large and ancient lakes Herder, Schliewen, et al., 2012;von Rintelen et al., 2007von Rintelen et al., , 2014von Rintelen & Glaubrecht, 2005), including flocks of freshwater fishes. ...
Streams provide an array of habitat niches that may act as environmental filters for fish communities. The tropical island of Sulawesi in Indonesia is located in the Wallacea, a region isolated by marine barriers from the Asian and Australian faunas. Primary freshwater fishes are naturally absent in the Wallacea, including Sulawesi's numerous coastal streams. Diadromous species are in contrast species‐rich in the area. The knowledge available on stream fishes in the Wallacea is largely restricted to taxonomic work and studies targeting single species groups, whereas baseline data on fish ecology remain extremely scarce. Such data and a deeper understanding of stream fish ecology are, however, urgently required for purposes such as informed management. We assumed that the stream fish assemblages are dominated by recruitment from the sea and are structured by macro‐ and microhabitat diversity. To test this hypothesis, we quantified the occurrence of individual fishes by point abundance electrofishing at 33 streams across Sulawesi. The 4632 fishes obtained represent 58 species out of 24 families. The native fishes recorded are mainly amphidromous (34 species), euryhaline (five species), and catadromous (five species). Gobiiformes make up the vast majority of records, dominated by Oxudercidae (22 species) and Eleotridae (five species). Only two of the species recorded are endemic to Sulawesi, including a single species strictly confined to freshwaters. Ten species, making up 6% of the fishes caught, are not native to Sulawesi. The outlying mean index (OMI) and BIOENV analyses suggest that effects on the scale of macro‐ and microhabitat shape fish assemblage composition, ranging from pH, conductivity, and temperature to current velocity, substrate, canopy cover, and elevation. Habitat niche use of species along the first two OMI axes is complementary and fine‐scaled, covering a wide range of the available habitat space. Juvenile and adult conspecifics share similar habitat niches in most of the cases. Niche breadths overlap, but niche specialization is significant in most of the species. Non‐native fishes link into the assemblages at the margins of habitat space, with substantial niche overlaps to native species. The present findings show that the native fish communities in coastal streams of Sulawesi are largely composed of species depending on access to the sea, highlighting the importance of connectivity down to the estuaries and sea. The ichthyofauna shows a rich diversity in habitat use, and the availability of alternative habitats along the altitudinal gradient provides plausible filters for species establishment. Non‐native fishes are locally abundant, pose substantial potential for changing communities, but are still stocked intentionally. We stress the need for incorporating the need for connectivity and maintained habitat quality into management decisions, and a critical evaluation of stocking activities.
... Cobitids, commonly referred to spined loaches, are a group of primary freshwater fish intolerant to water salinity (Myers, 1949;Nelson et al., 2016) distributed throughout Asia, Europe and North Africa (Nalbant et al., 2001;Kottelat & Freyhof, 2007). At present, the family of Cobitidae includes 232 valid species spread across 18 valid genera (Fricke et al., 2023). ...
Cobitis maroccana, also known as the Moroccan loach, is an endemic freshwater fish found in the rivers of the Loukkos and Sebou basins in Morocco. In order to gain a better understanding of the genetic differentiation within C. maroccana from the Loukkos and Sebou populations, a comprehensive study was conducted, focusing on the mitochondrial cytochrome b gene. A total of 30 sequences of the complete cytochrome b (1140 bp) were obtained from C. maroccana specimens. Through a combination of phylogenetic analysis, phylogeographic assessments, as well as the estimation of the Fst index, the research outcomes revealed significant genetic differentiation between the two juxtaposed basin populations. Notably, each of these basins displayed unique and distinct haplotype groups within the C. maroccana specimens. These intriguing findings strongly suppose that the populations in the Loukkos and Sebou basins have become reproductively isolated from each other over time, indicating limited or no interbreeding between them.
... El recambio de especies en los ambientes se analizó mediante la disimilitud de Jaccard representada en un dendrograma. Las especies se clasificaron de acuerdo con su tolerancia a la salinidad en primarias (dulceacuícolas que son intolerantes al agua salada), secundarias (dulceacuícolas que presentan tolerancia a la salinidad) y periféricas (peces marinos que pueden estar asociados a ambientes estuarinos y ríos) (Myers, 1949;Jiménez-Prado et al., 2015). En cuanto a su origen biogeográfico, se clasificaron en endémicas, nativas y exóticas. ...
Our study focuses on the fish fauna in the lower Pisco River in Ica, central coast of Perú. We examined the specimens deposited in the MUSM Ichthyological Collection including field evaluations in the main channel of the Pisco River, the Pisco Playa Wetland, the Morón Lagoon, and the Poza Lagunillas, as well as records from the available literature. We recorded 13 fish species belonging to eight families and eight orders, with Cichlidae as the most diverse family, with four species. Lebiasina bimaculata represents a new record for the ichthyofauna of the Pisco River. Species richness varied according to the evaluated environment, with Pisco Playa Wetland and the Pisco River as the environments with the highest diversity, hosting nine and eight species, respectively. Regarding the species composition, Andinoacara stalsbergi, Poecilia reticulata, and Oreochromis sp. were present in the four aquatic environments evaluated and could be considered core species, while Basilichthys semotilus was recorded exclusively in the Pisco River. In terms of salinity tolerance, one primary, 11 secondary, and one peripheral species were identified. As for their origin, exotic species represented 53.8% of the total richness, with Oreochromis sp. and P. reticulata present in all the environments evaluated. Our study updates the knowledge of the ichthyologic richness in the lower Pisco River. It provides a valuable tool for managing, divulging, and conserving the aquatic biota from this region
... The relationship between different diversity estimates measured at increasing spatial scales (α-, β-and γ-diversity) is affected by several factors. Movement of species among habitats within estuarine ecosystems is spatially and temporally dynamic as it involves interactions between spatial and physical properties (e.g., estuarine mouth open and closed phases), life history, and physiological tolerances (e.g., salinity tolerance), all of which contribute to differences in diversity between systems (Myers, 1927;Yáñez-Arancibia et al., 1994;Matthews, 1998;Habit et al., 2003;Cowan et al., 2013). In addition, the proportion between specialists vs generalists fish species in the metacommunity can affect the occupancy of estuarine systems (Heino, 2013). ...
Estuarine systems are highly productive ecosystems with diverse fish communities that provide valuable ecosystem services. The structure and ecology of fish communities in the estuarine systems of the Mesoamerican Barrier Reef System region (MBRS) is largely unknown. Here, the fish communities and their relationship with environmental variables were investigated for the first time in sixteen estuarine systems along the Honduran coast of the MBRS. The estuarine systems included estuarine lagoons and estuaries with different mouth dynamics , such as permanently open estuarine systems (POE) and temporary open-closed estuarine systems (TOCE). A total of 154 fish species were identified. Estuarine lagoons exhibited higher abundance and species richness, with Karataska and Chachaguala having the highest species richness (~80 species). Overall, higher diversity was observed in POE systems and during the open mouth phase, likely due to higher dispersion rates. Fish species were classified into different functional groups based on their utilization of estuarine environments. The most abundant category was marine fish (50.6 %), with marine stragglers and marine estuarine-opportunists as the dominant guilds within this category. Freshwater, estuarine, and diadromous fish categories contributed less but similarly. Fish communities in estuarine lagoons and estuaries showed clear differences, although they shared some common species. Estuarine lagoons communities were dominated by the marine category and marine-estuarine-opportunists, while those of estuaries were characterized by the freshwater category and freshwater-estuarine-opportunists. The occupancy varied greatly, with some species present in multiple estuarine systems and others restricted to a single system. Species contribution to β-diversity (SCBD) revealed that species present in a single system made the greatest contribution. Local contribution to total β-diversity (LCBD) ranged between 1.48 and 20.10 %, with the Chachaguala estuarine lagoon being the main contributor. In addition to geomorphological features and estuarine mouth state, distance-based multivariate linear model (DistLM) showed that salinity, pH, bottom vegetation, and dissolved oxygen contributed significantly in explaining the fish metacommunity variation. This study shows the importance of environmental filtering in shaping local fish communities in the MBRS estuarine systems. However, further research is needed to understand the role of dispersion pathways and rates for the integral management of the estuarine fish metacommunity in the region.
... Exposure to high salinities in L. perugiae has been shown to decrease metabolic rate [25], increase the production of Na + /K + -ATPase and oxidative phosphorylation proteins in the gills [23], and reduce adult body size [23]. Though predominantly associated with freshwater habitats, many fishes in the family Poeciliidae are able to tolerate a broad range of salinities, a factor potentially responsible for facilitating their dispersal across a wide geographic range [26][27][28][29]. While the mechanisms and consequences of salinity tolerance at the biochemical and physiological levels have been a focus of research in poeciliids [23,[30][31][32][33], the genetic and regulatory underpinnings of salinity tolerance have yet to be investigated in this family. ...
Salinity gradients act as strong environmental barriers that limit the distribution of aquatic organisms. Changes in gene expression associated with transitions between freshwater and saltwater environments can provide insight into organismal responses to variation in salinity. We used RNA-sequencing (RNA-seq) to investigate genome-wide variation in gene expression between a hypersaline population and a freshwater population of the livebearing fish species Limia perugiae (Poeciliidae). Our analyses of gill gene expression revealed potential molecular mechanisms underlying salinity tolerance in this species, including the enrichment of genes involved in ion transport, maintenance of chemical homeostasis, and cell signaling in the hypersaline population. We also found differences in gene expression patterns associated with cell cycle and protein folding processes between the hypersaline and freshwater L. perugiae. Bidirectional freshwater-saltwater transitions have occurred repeatedly during the diversification of fishes, allowing for broad-scale examination of repeatable patterns in evolution. We compared transcriptomic variation in L. perugiae with other teleosts that have made freshwater-saltwater transitions to test for convergence in gene expression. Among the four distantly related population pairs from high- and low-salinity environments that we included in our analysis, we found only ten shared differentially expressed genes, indicating little evidence for convergence. However, we found that differentially expressed genes shared among three or more lineages were functionally enriched for ion transport and immune functioning. Overall, our results, in conjunction with other recent studies, suggest that different genes are involved in salinity transitions across disparate lineages of teleost fishes.
... From this, we see that the diet of Bairdiella ronchus from the Caribbean region is not as diverse as the diet of their species counterparts in Brazil, South America. This is likely due to continental species occupying wider habitat ranges and the higher biodiversity that exists on the South American continent (Myers 1949). ...
... Salinity tolerance is one of several important physiological features that determine invasion success and the pattern of dispersal of introduced aquatic organisms between freshwater bodies through brackish waters (Cognetti and Maltagliati 2000;Schofield et al. 2009;Capps et al. 2011). Loricariidae is considered a strictly freshwater family of fish in their native range throughout the Neotropics (Myers 1949). Nonetheless, Loftin (1965) found that Hypostomus aspidolepis could survive immediate immersion in 30 PSU and 40 PSU if acclimated. ...
In the last decade, invasive suckermouth armored catfish Pterygoplichthys spp. spread among many river systems of Vietnam. Extended distribution of armored catfish might be associated with using brackish water in estuaries for fish spread from one river system to another. The first goal of our study was to assess the occurrence of armored catfish in the estuary of the Da Rang River (Phu Yen Province, Vietnam) and their distribution depending on the horizontal salinity gradient (4–25 PSU). Fish were mainly caught by stationary bottom traps in water salinity from 4 PSU to 18 PSU. The second goal of our study was to experimentally evaluate the ability of armored catfish to move and breathe in seawater (33 PSU). Fish moved in horizontal and vertical planes after transfer into seawater during the first 15 minutes. Fish moved around less by the 13 th –15 th minutes in seawater. Armored catfish moved around more in seawater than in freshwater. The exposure to seawater for 6 minutes led to deterioration of fish breathing. The results of our field and experimental studies established that armored catfish are found and able to move in brackish waters but avoid high salinity water. These facts provide support for the hypothesis of armored catfish invasion through the estuaries and coastlines.
... The data on trophic categories (omnivores, carnivores, planktivorous, herbivorous, larvivores, and insectivorous), existing habitat (a dweller of riverine habitats as well as hill streams, migratory, estuaries, and floodplains) and population trends were studied by IUCN Bangladesh (2015), the Web-based database like FishBase (Froese and Pauly, 2015) and published articles (DoF, 2018;Pandit et al., 2021;Sarker et al., 2022;Lakra et al., 2010). The present status of SIS was classified into 4 groups namely abundantly available (AA); available throughout the year (species presence: 76-100%); commonly available (CA); frequently found in small numbers throughout the year (species presence: 51-75%); moderately available (MA); infrequently seen in the study area (species presence: 26-50%) and rarely available (RA); found intermittently in very limited number (species presence: 1-25%) were considered based on respondent's observations and species presence (%) (Jadhav et al., 2011;Myers, 1949). The commercial value of the species collected was determined by using criteria specific to their use as food (including adequate growth in unit time and reaching maximum size), sport (including angler preference), or ornamentation (including beautiful color, shape, and size, banding pattern, hardiness, transparent body, calm behavior, and adhesive suckers). ...
This study investigated diversity, availability, current status, population trend, threats and conservation status of SIS in floodplain-rich haorbasin from September 2017 to April 2018. A total of 140 SIS belonging to 35 families and 89 genera were collected from 43 sampling sites (10 in arats/wholesale fish markets, 16 in retail markets, and 17 in fishing locations). Cypriniformes were the most diverse group. 47%, 29%, 14% and 9% of species were moderately available, commonly available, rarely available and abundantly available, respectively. Fish belonging to Cypriniformes and Siluriformes were under moderately available and rarely available categories. Carnivorous was dominant group (49%). National and global population trends of 44% and 13% recorded fish were declining (Perciformes, Siluriformes and Clupeiformes were dominant), whereas most of the species don't have enough biological informationstatus. Out of the 140 species, 4 belong to `critically endangered`, 18 `endangered` and 14 `vulnerable` at national level, beside the order Osteoglossiformes, Sygnathiformes and Cypriniformes were more threatened. Additionally, Mastacembelus oatesiiand Rita ritawere endangered and Channa orientalisand Barilius dogarsinghiwere vulnerable at the global level. Indiscriminate fishing, poisoning, illegal fishing, siltation, pollution and invasive species posed the greatest threat to fish diversity. Climatechange is hard to predict and drastically changing fish habitats and putting SIS at risk. Eco-friendly modern fishing technology, restoration, and potent conservation measures are urgently needed at multiple scales to conserve the fish fauna.
... Zoogeographically, FW fish have been classified differently by different workers. Although the classification made by Myers [14] have been proved to be the most useful, and widely accepted one, the FW fish of marine origin had been further classified as `peripheral FW forms' by Nichols [15] and Darlington [16] which has also been accepted by many recent fish geographers. Incidentally, the ichthyofauna of this region, by and large, have been found to belong to the following categories [17]: ...
... Fishes were identified with available keys (e.g., Allen and Robertson 1994, Allen et al. 1995, Castro-Aguirre et al. 1999, Miller et al. 2005, scientific names and authorities were corroborated following Fricke et al. (2020). The ecological classification of fishes, considering their salt-tolerance, followed the criteria proposed by Myers (1949) and Castro-Aguirre et al. (1999): catadromous, estuarine, euryhaline, stenohaline and secondary freshwater. Species with commercial value were identified using the work of García-Morales (2007). ...
Discards from artisanal shrimp fisheries in coastal lagoons of Mexico have been little analyzed, especially in the southern Pacific. This study aimed to evaluate the composition and community structure of the discarded ichthyofauna in the artisanal shrimp fishery in the coastal lagoon system Chantuto-Panzacola, Chiapas, Mexico. Samples were obtained during the period September-December of 2009. We carried out four monthly samplings in two fishing spots situated in an estuarine channel; two stow-net-like (locally known as “copos”) were used in a six-hour period. Richness, abundance, dominance, diversity, and biomass of the discarded ichthyofauna were obtained. Discard was made up of 71 species, 55 genera, 31 families, and 13 orders. The best represented families were Ariidae, Sciaenidae, Engraulidae, Carangidae, Gobiidae and Gerreidae. The best represented ecological component was the euryhaline species (40), followed by stenohaline species (25), secondary freshwater species only were represented by one species.
The dominant species were Achirus mazatlanus, Anchoa lucida, Dormitator latifrons, Cathorops liropus
and Stellifer wintersteenorum. The highest discarded biomass, richness and abundance were measured in
October, while the highest diversity was obtained in December. Average ratio kg of shrimp: kg of discard
was 1:1.9. This is the first study that quantifies the impact of the discards over the fish community in the
artisanal shrimp fishery in coastal lagoons of a protected natural area in Chiapas.
Keywords: Small-scale fishery, ecology, fishes, penaeids, Chiapas
... Coastal river basins have high species richness, where fish species coexist and are classified as primary or secondary freshwater species, or as peripheral species based on salt tolerance (Myers 1949;Blanco-Libreros and Carbajal-Quintero 2015;Jiménez-Prado et al. 2015). Primary species are physiologically intolerant to salinity, whereas secondary species are found largely in estuaries and enter freshwater areas. ...
To update the knowledge of the ichthyofauna of the Tumbes River basin, we provide a list of species. We report 47 species of fishes, grouped into 23 families and 11 orders. Characiformes was the most diverse order with 12 species (25.5% of the total richness), followed by Carangiformes with eight species (17%). In our study, two species are newly reported from this river basin: Pseudophallus starksii (Jordan & Culver, 1895) and Evorthodus minutus Meek & Hildebrand 1928. According to salinity tolerance, the ichthyofauna is composed of 20 primary, 14 secondary, and 13 peripheral species. Despite having the highest diversity of fish on the Peruvian Pacific slope, the Tumbes river basin is one of the most polluted coastal drainages. This study compiles information on the ichthyofauna of the entire basin, increases the known diversity of freshwater fish from trans-Andean drainages in Peru, and can be used in the management and conservation of the Tumbes River.
... The small number of freshwater fishes recorded may be explained by the high salinity of the sampled estuaries or factors identified by Whitfield (2015), including strong competition and predation with marine species, the abundance of avian predators, the unavailability of upstream freshwater food sources, and habitat disconnectivity due to damming. Moreover, the observed continental freshwater fishes are physiologically secondary or peripheral and are known to tolerate moderate levels of salinity (Myers 1949). The freshwater families recorded by Oliveira (1976) and Alves and Soares-Filho (1996) in the estuary of the Jaguaribe river (Ceará) point to a richer freshwater ichthyofauna in the recent past. ...
We extensively surveyed eight estuaries along the coast of the state of Ceará in northeastern Brazil. We
include local samples and data compiled from online databases and the literature. Our sampling resulted in a
checklist of the estuarine fish fauna, 126 species, and provides original information from some of the estuaries.
Most of the sampled marine species are widely distributed, and many are important commercial species for artisanal fisheries. The addition of records from existing inventories and online collections increases the number of
species to 245, of which 11 are threatened (Critically Endangered or Vulnerable) and six are introduced. Our study
provides an updated list of fish species of the estuaries along the semiarid coast of Brazil and is intended to support
further research, conservation, and management efforts.
... Thus, the historical connection among river basins, as well as the fish tolerance to seawater are important factors to understand contemporary geographical patterns of freshwater fishes (Darlington, 1948;Filipe et al., 2009). Myers (1938Myers ( , 1949 recognised that the distribution of fish is mediated by their different ability to survive and disperse through seawater, and proposed a classification of inland fish based on their ecoevolutionary history and euryhalinity. Darlington (1948) reviewed and simplified this classification of inland fish into three major eco-evolutionary groups (hereafter, Darlington's divisions): (1) primary fish, whose ancestors entered inland waters much earlier, cannot survive in seawater and are thus strictly confined to fresh water; (2) secondary fish, which mostly live in fresh waters but show some salt-tolerance and can thus may survive in seawater; and (3) peripheral fish, which occur in fresh waters but have high salt-tolerance, such as diadromous or species of marine origin. ...
Fresh waters are among the most biodiverse ecosystems globally but, at the same time, also the most threatened. Serious menaces to freshwater ecosystems are, for instance, habitat alteration, invasive alien species, pollution, water abstraction and climate change. One of the most pervasive indicators of anthropogenic impacts on rivers is hydrological alteration caused by artificial barriers, which is known to reinforce the decline of local biodiversity and ecosystem services, and the species homogenisation of inland fish communities. Previous studies showed that the novel lentic habitats created by dams and habitat modifications occurring downstream of dams favour the establishment of alien fish, as many of them commonly prefer lentic habitats with warmer water temperatures compared with native fish. Thus, jointly studying species distribution patterns and species traits and their evolutionary history provides an essential link to better understand species’ responses to environmental change and biological invasions, and to design effective management tools and policies. For instance, swimming performance (often measured in the laboratory as critical swimming speed [Ucrit]) is a particularly important trait in aquatic organisms, mediating their fitness, habitat selection or survival. However, there are few studies that evaluated its evolutionary relationship with other traits, with fish distribution patterns or with invasion success in freshwater ecosystems.
The Iberian Peninsula is a well-suited region to study the effects of climate, land use change and hydrological alteration on the distribution of native and alien fish species, due to its complex orography and diverse climate and ichthyofauna. In fact, the Iberian Peninsula is one of the most impacted regions by dams (over 1500 large dams fragment Iberian rivers) and invasive species (32 established alien fish species). Thus, this thesis aimed to evaluate the relationship of distribution patterns and traits of inland fishes, and to understand the ecological filtering with a special focus on hydrological alteration using the Iberian ichthyofauna as a study system. The research performed was structured in five chapters and included: (1) a compilation of Iberian inland fish trait data and corresponding reliability analysis of the different data sources; (2) the analysis of swimming capacity of native and alien Iberian inland fishes using random forests models, generalised linear mixed model and linear models; and (3) studies of the distribution patterns and niche characteristics of Iberian fish using species distribution models and the outlying mean index, as well as the analysis of relationships of these distribution patterns with fish traits using phylogenetic and non-phylogenetic approaches.
... Some of the authors (Caps et al., 2011;Brown et al., 2013;Kumar et al., 2018) support the similar hypothesis for other regions of this species dispersal. Armored catfishes considered, as a rule, freshwater representatives of the order Siluriformes (Myers, 1949), nevertheless they are able to enter brackish waters (Stevens et al., 2006;Barletta and Blaber, 2007) and tolerate elevated water salinity up to 16% (Capps et al., 2011). In view of the widespread distribution of armored catfishes in Vietnam and their possible impact on the native ichthyo-fauna, it seems important to obtain information about their tolerance to brackish water. ...
The paper presents the results of the study of survival, the concentrations of thyroid hormones and ions of armored catfish of the genus Pterygoplichthys at increasing salinity of water. A stepwise (every two days) increase in water salinity from 0 to 12.5‰ leads to a significant increase in the concentration of Na+, K+, Cl–, Ca2+ ions in the blood of fish, but does not affect the level of thyroid hormones (free and total triiodothyronine, thyroxine) and the calculated ratio of these hormones. The data indicate a low involvement of the thyroid gland in the osmoregulation of armored catfish. It is confirmed that some specimens of armored catfish can tolerate water salinity up to 15‰ for 2 days. The possibility of dispersal of armored catfish along estuaries to neighboring river systems is discussed.
... Recently, freshwater bioregions were proposed based on obligate freshwater fishes (primary and secondary sensu Myers, 1949) using quantitative approaches for Central America (Matamoros et al., 2015) and for the contiguous USA (Matamoros et al. 2016), lying south and north of NoMA, respectively. Studies in Central America and southern Mexico (Matamoros et al., 2015) indicate that the southern Mexican BRs of Miller et al. (2005) do not stop at the international boundary, but extend into Guatemala on the Caribbean slope and Honduras on the Pacific slope (Matamoros et al., 2015). ...
Northern Middle America (NoMA) is considered a transition zone between the Nearctic and Neotropical biogeographic realms. In this region, Nearctic and Neotropical freshwater fishes create regional faunas of mixed origin, but their general biogeographic patterns have not been quantified. To identify such patterns, we delineate biogeographic regions (BRs) and major biogeographic barriers of NoMA and summarize patterns of faunal similarity among BRs. We used clustering analysis on a presence-absence matrix of primary and secondary freshwater fishes to group 97 level-6 HydroBASINs units spanning NoMA into BRs. We assessed statistical support of clusters using one-way analysis of similarity and implemented a species-indicator analysis. We delineated biogeographic barriers with the software Barrier 2.2 and determined faunal similarity among BRs using beta diversity-Jaccard dissimilarity and producing a minimum-spanning tree. Seven statistically distinctive and geographically coherent BRs were delineated and described. Barrier analysis identified three major barriers within NoMA. The first barrier combines the Sea of Cortés (Gulf of California) and Sierra de Juárez-Cerro Gordo highlands. The second combines the Trans-Mexican Volcanic Belt, Sierra Madre del Sur, and Sierra Madre de Chiapas highlands. The third combines the Río Grande Rift, Sierra Madre Occidental, and Mesa Central highlands. Faunal dissimilarity was very high among BRs, with lowest dissimilarity (92%) between the Balsas-Nacaome and Grijalva-Usumacinta BRs. Boundaries of NoMA BRs do not correspond with political boundaries. We concluded that bioregions of NoMA are faunally distinct, with limited overlap due to presence of strong, long-standing geographical barriers enhanced by aridity in the Nort
... Cyprinids are primary freshwater fish intolerant to water salinity (Myers 1938;Fenolio et al. 2013;Nelson et al. 2016). As a result, their dispersal is limited to river basins only; they are unable to move across disconnected ones either across marine waters (Myers 1949;Darlington 1957). ...
Conservation of biodiversity entails not just the preservation of specific taxa, but also genetic diversity. Despite the fact that molecular data appear to be crucial for freshwater fish conservation management, the information about genetic diversity of the genus Luciobarbus Heckel, 1843 populations in Morocco is still very rare. Accordingly, this study’s main purpose was to present genetic and biogeographic information of nine Luciobarbus species out of 15 Luciobarbus species native to Morocco. Sequencing of the complete cytochrome b gene (1140 bp) confirmed the presence of two evolutionary lineages of Luciobarbus in Morocco and displayed low to high level of genetic diversity within Luciobarbus populations. Populations with the largest size had the highest level of genetic diversity, according to our findings. Moreover, the “star-like” shape of the haplotype networks along with low and insignificant value of the Harpending raggedness index supported the hypothesis of population expansion in Luciobarbus populations. Nevertheless, additional investigations should ideally be undertaken separately for each species in order to untangle genetic diversity trends.
... There is no doubt, however, that Matthew's views deserve the most careful consideration, and it is unfortunate that he did not live to write the proposed enlarged and revised edition of his work. (Myers, 1938, p. 341) During his career, Myers published numerous zoogeographic analyses of freshwater fishes applying Matthewian principles (e.g., Myers, 1938Myers, , 1949Myers, , 1951Myers, , 1954Myers, , 1963Myers, , 1966. They were praised by several authors, including Darlington (1957), who admitted that they have been a key contribution to his understanding of the distributional patterns of freshwater fishes. ...
Climate and evolution (Matthew, 1915) represents an important contribution to evolutionary biogeography, that influenced several authors, notably belonging to the "New York School of Zoogeogra-phy"-a research community including Matthew, Schmidt, Myers and Simpson-accepted Matthew's "Holarcticism" (north temperate centers of origin) and the permanence of ocean basins and continents, whereas others, especially panbiogeog-raphers and cladistic biogeographers, were extremely critical and reacted against these ideas. "Holarcticism" has been falsified and rejected by dispersalists and the "New York School of Zoogeography" disappeared in the 1970s. Matthew, however, continues being identified by panbiogeographers and cladistic biogeographers as a key representative of classic dispersalism, helping provide some cohesion to their research communities.
... The composition of Common Snook and Mexican Snook diets presented spatial variability that may be associated with the differences in the freshwater and saltwater inputs received by the PR and PA systems. The PR system presents greater salinity fluctuations due to the constant inflow of freshwater from the Palizada River and its direct (Myers 1949;Miller 2009), which were important in the Common Snook and Mexican Snook diets in this system. The Levin's index results for Common and Mexican snooks were mainly related to the high proportion of fish remains in their diet (>35%). ...
Coexisting species often develop resource‐partitioning mechanisms to reduce their direct competition and optimize energy harvesting. Common Snook Centropomus undecimalis and Mexican Snook C. poeyi are carnivorous fish that coexist in estuaries of the Usumacinta River delta, in the southern Gulf of Mexico, and play an important role for fisheries and economy in this region. We analyzed spatial, temporal, and ontogenetic variability in trophic dynamics and distribution of Common and Mexican snooks. To identify patterns of trophic resource partitioning, we analyzed stomach content and stable isotopes (δ13C, δ15N) of the two species. Fifty‐one prey items were identified, with fish remains being the most abundant component (>35%). The two snook species appeared to be specialized carnivores of the third or fourth trophic level. Diet comparison indicated significant differences among species: Common Snook presented a higher proportion of fish from the families Engraulidae, Clupeidae, and Elopidae, while Mexican Snook consumed a higher fraction of fish from the families Cichlidae, Poeciliidae, and Loricariidae. The diet also presented significant variations between size‐classes. Small‐sized (<350 mm SL) Common Snook showed significantly higher reliance on invertebrates than large‐sized fish (>500 mm SL). Medium‐sized (351–499 mm SL) Mexican Snook consumed a higher proportion of Poeciliidae fish than small‐sized or large‐sized fish. The diet of the two snook species also presented important differences among seasons and sites. Trophic niche overlap between Common and Mexican snooks varied among systems, with higher overlap in the Pom−Atasta system than in the Palizada River. This study indicates that Common Snook and Mexican Snook have developed strategies for spatial partitioning of resources that favor their coexistence in the Usumacinta River delta.
... To distinguish among species with varying affinities to continental waters, freshwater fishes worldwide may be classified into three categories based on their physiological tolerances to saltwater (Myers, 1949). Primary freshwater fishes are strictly confined to freshwater, and have little or no tolerance to salty or brackish waters. ...
This chapter provides a brief overview of freshwater fish diversity globally, the factors underlying diversity patterns among and within river basins and phylogenetic groups, and the main threats to this diversity in the Anthropocene. Continental freshwaters represent among the most diverse and species-dense habitats on Earth, with almost 18,000 fish species (> 50% of all fish species) compressed into just < 0.5% of the total surface area, and a miniscule (< 0.01%) proportion of the planetary water supply. Freshwater fish diversity reaches a peak in the large lowland tropical river basins, in particular in the Amazon, Congo and Mekong basins. At an intercontinental scale, variability of freshwater fish species richness is related to the total volume and heterogeneity of aquatic habitats, and the stability of these environments over evolutionary time scales. Regional fish species richness, species composition, and functional traits all change predictably along environmental gradients from headwater to estuary (the river continuum concept). In most parts of the world, the abundance and diversity of riverine fishes is strongly related to the regular exchange of nutrients and organic matter associated with adjacent floodplains (the flood pulse concept). Freshwater fishes currently face a multitude of threats in all parts of the world, which will lead to severe losses in abundance and diversity in the absence of concerted conservation actions.
... El número total de especies reportado incluye registros publicados en revisiones previas (e.g., Angulo et al., 2015;2017;2018;, & Álvarez-Calderón et al., 2018 así como datos sin publicar. Del total de familias listadas 11 son, según la propuesta de Myers (1949), dulceacuícolas primarias (i.e., dulceacuícolas estrictas), 7 son dulceacuícolas secundarias (i.e., usualmente restrictas a ambientes dulceacuícolas, pero con tolerancia a condiciones variables de salinidad) y 35 son periféricas (i.e., típicamente marinas o asociadas a ambientes costero-estuarinos con capacidad de incursionar en ambientes dulceacuícolas) (Cuadro 1). La clave resultante se presenta a continuación: ...
Introducción:
El conocimiento sobre la composición taxonómica de la fauna de peces de agua dulce de Costa Rica ha cambiado sustancialmente en las últimas dos décadas. No solamente por la adición de nuevas especies y táxones supra-específicos, sino también por reordenamientos y cambios taxonómicos en los diferentes niveles jerárquicos. Las claves taxonómicas disponibles se publicaron hace más de 20 años y están desactualizadas.
Objetivo:
Brindar información actualizada, en lenguaje sencillo, para la identificación de todas las familias costarricenses de peces continentales e insulares.
Métodos:
Utilizamos literatura especializada, colecciones de museos y especímenes recolectados recientemente para actualizar las claves disponibles tomando como referencia una lista de familias del 2013.
Resultados:
La clave dicotómica ilustrada, que cubre 53 familias, se basa en características externas relativamente fáciles de identificar. También incluimos información sobre la composición de especies, distribución general y uso del hábitat. Conclusión: Esta clave permite la identificación de 274 especies de peces costarricenses a nivel de familia, como base para su identificación a categorías más bajas.
... The remaining 6% are made up of 23 different orders, mostly peripheral fish of marine origin. The ecophysiological classification in primary, secondary, and peripheral freshwater fish refers to the origin of the groups and their tolerance to salinity (Myers, 1949(Myers, , 1966. Primary freshwater fish groups are those originated in freshwater and intolerant to salt water, such as electric eels (Gymnotiformes) and tetras and relatives (Characiformes). ...
... Voucher specimens were deposited at the ichthyological collection of the Museum of Zoology of the Universidad de Ciencias y Artes de Chiapas in Tuxtla Gutiérrez, México (MZ-P-UNICACH). Species were allocated to five ecogeographical affinities according to their salinity tolerance (Myers 1949, Yáñez-Arancibia et al. 1985, Torres-Orozco 1994: primary freshwater (species found strictly in freshwater systems and are physiologically intolerant to salinity), secondary freshwater (species frequently found in freshwater systems but with some tolerance for estuarine conditions and dispersal capacity through marine environments), estuarine resident (species that are residents in brackish waters, salinity 5-10, but with tolerance to abrupt changes in salinity), marine euryhaline (species that usually tolerate salinities from 10 to 18) and marine stenohaline (species that usually tolerate salinities from 18 to 30). Fish species were also allocated to trophic guilds considering information on food items from Froese & Pauly (2017) and other studies in the eastern Pacific (Gómez-González et al. 2012, Robertson & Allen 2015, Romero-Berny et al. 2018. ...
We analyzed the local variation of fish assemblages in four coastal lagoon systems surrounded by mangroves, draining into the Gulf of Tehuantepec (Pacific versant of Mexico), and determined the spatial patterns of alpha, beta, and gamma diversity. Fish were sampled between 2004 and 2016 at 63 sites using cast nets. The collected data were supplemented with information obtained from published works for three other coastal lagoons for the regional analysis. Local richness was high (89 species in a total of 19,017 specimens in four systems). Locally, dissolved oxygen, depth, and distance to mangrove were variables that significantly affected richness and abundance of fish in one or more systems. The Chantuto-Panzacola system showed the highest richness, significantly different from the other systems, although the trophic groups were similar. Regionally, two, Istmo and Soconusco complexes were identified, whose turnover rate (0.36) and gamma diversity (176) increased from north to south. Fish species richness and abundance increased with growing mangrove area, both locally and regionally, making this a highly explanatory variable. The Gulf of Tehuantepec is an environmentally heterogeneous region, with ecological patterns defined according to the spatiotemporal scale, which should be considered in the delineation of ecoregions and coastal management planning.
... On the other hand, trans-oceanic dispersal over hundreds or thousands of kilometers, followed by successful colonization of a new continent, appears extremely improbable, given that cichlids are found almost exclusively in freshwater. Whereas several cichlid species occur in brackish-water estuaries and some species are known to tolerate marine saltwater conditions (Myers 1949;Stickney 1986;Uchida et al. 2000), none have ever been observed in the open ocean, more than a few miles from the coast (Conkel 1993; Greenfield and Thomserson 1997). Thus, a long-standing debate has centered on the relative probabilities of the two alternative scenarios, Gondwanan vicariance despite long ghost lineages, or trans-oceanic dispersal despite a common freshwater lifestyle (Vences et al. 2001;Murray 2001a;Chakrabarty 2004;Sparks and Smith 2005;Genner et al. 2007;Smith et al. 2008). ...
Divergence-time estimation based on molecular phylogenies and the fossil record has provided insights into fundamental questions of evolutionary biology. In Bayesian node dating, phylogenies are commonly time calibrated through the specification of calibration densities on nodes representing clades with known fossil occurrences. Unfortunately, the optimal shape of these calibration densities is usually unknown and they are therefore often chosen arbitrarily, which directly impacts the reliability of the resulting age estimates. As possible solutions to this problem, two non-exclusive alternative approaches have recently been developed, the "fossilized birth-death" model and "total-evidence dating". While these approaches have been shown to perform well under certain conditions, they require including all (or a random subset) of the fossils of each clade in the analysis, rather than just relying on the oldest fossils of clades. In addition, both approaches assume that fossil records of different clades in the phylogeny are all the product of the same underlying fossil sampling rate, even though this rate has been shown to differ strongly between higher-level taxa. We here develop a flexible new approach to Bayesian node dating that combines advantages of traditional node dating and the fossilized birth-death model. In our new approach, calibration densities are defined on the basis of first fossil occurrences and sampling rate estimates that can be specified separately for all clades. We verify our approach with a large number of simulated datasets, and compare its performance to that of the fossilized birth death model. We find that our approach produces reliable age estimates that are robust to model violation, on par with the fossilized birth-death model. By applying our approach to a large dataset including sequence data from over 1000 species of teleost fishes as well as 147 carefully selected fossil constraints, we recover a timeline of teleost diversification that is incompatible with previously assumed vicariant divergences of freshwater fishes. Our results instead provide strong evidence for trans-oceanic dispersal of cichlids and other groups of teleost fishes.
... The family Loricariidae is considered a strictly freshwater family of fishes in their native range throughout the Neotropics (Myers, 1949). However, scattered collection records of Pterygoplichthys spp. in saline waters (i.e. 5 -8 g.L -1 ) in their introduced ranges have raised questions regarding the breadth of their physiological tolerance to salinity (Capps et al., 2011;Brion et al., 2013). ...
It has been suggested that suckermouth armoured catfishes of the genus Pterygoplichthys Gill, 1858 (Siluriformes: Loricariidae) might use brackish water systems as a means to disperse between freshwater bodies. This study aimed to explore the dynamics of Pterygoplichthys spp. distribution in relation to salinity gradient and provide population characteristic data, namely length, weight, condition factors by sampling the Co Chien and Ham Luong rivers, Mekong Delta, Vietnam. Contrary to initial predictions, there was neither evidence for the presence of Pterygoplichthys spp. in brackish waters in the Mekong Delta nor for the fishes' colonisation of an area that fluctuates seasonally between freshwater and brackish water. Length-weight relationship and condition factor of the fishes demonstrated negative allometric growth and good physiological condition. The findings from this study could help fishery managers to map out the distribution of Pterygoplichthys spp. in the Mekong Delta as well as raise awareness on the perils of releasing aquarium pets.
... To elaborate the list supporting this study, only freshwater fish species formally described until December 2019 were considered. Despite the fact that freshwater species were defined as those known to spend a significant part of their life cycle in low salinity (<0.5 ppt) continental waters (Myers 1949;Berra 2001), in the present study only primary freshwater fishes were considered. ...
This work was carried out from the assessment of the conservation status of the freshwater ichthyofauna from Bahia State. The inventory data and species distribution were obtained from the specialized scientific literature and representative ichthyological collections. A total of 281 native species was recorded in Bahia State, distributed in the Northeastern Mata Atlantica (NMA) and São Francisco (SFR) freshwater ecoregions. There was a larger number of species in the NMA (187 spp.), composed by several coastal basins, than in the SFR (134 spp.), composed by São Francisco river basin. Among the 30 families recorded, Characidae and Rivulidae were the most representative, with 53 and 48 species, respectively. The conservation status of 214 species was assessed and 33 of them (15%) were included in the IUCN threat categories. Of these, 11 species were classified as vulnerable (VU), 12 as endangered (EN), and 10 as critically endangered (CR). Most threatened species (n = 14) belongs to the family Rivulidae. The larger number of threatened species in the NMA: (n = 23) is mainly related to the high endemism of restricted-range species associated with the human occupation impacts along the coastal regions. In the SFR, most of threatened species are annual killifishes, which are locally disappearing due to increasing degradation of their temporary habitats.
... Los peces de agua dulce pueden ser clasificados de acuerdo a niveles de tolerancia a cambios de salinidad en el agua. Myers (1949) los clasificó en tres grandes grupos; peces primarios, como aquellas especies estrictamente de agua dulce que no toleran aguas salobres y se distribuyen de cuenca a cuenca y nunca por vía marítima. Peces secundarios, como aquellas que evolucionaron en agua dulce a partir de grupos marinos que son capaces de tolerar aguas salobres y un tercer grupo que se clasifican como periféricos o de transición que son aquellos peces de origen marino que toleran agua dulce y habitan en ellas de manera esporádica. ...
... M. urophthalmus has been introduced, it has been hypothesized that their high tolerance to salinity and potential to use costal waterways has facilitated the colonization and expansion of M. urophthalmus from southern Florida to the mid and northern latitudes of the state (Myers 1949;Paperno et al., 2008). Empirical studies addressing how M. urophthalmus managed to reach island localities and cope with salinity barriers that potentially present extreme physiological constraints, especially at this distance from the mainland, are important areas for future work. ...
Here we report the first record of the Mayan cichlid, Mayaheros urophthalmus, occurring on an offshore island 70 km from the mainland, the most distant record from the mainland to date. Specimens were collected during several ichthyological surveys on the island of Guanaja, Honduras in November 2019. Mayan cichlids are euryhaline fishes that perform very well in fresh, brackish and marine waters. It has been hypothesized that their high tolerance to salinity and potential of using costal waterways has facilitated the colonization and expansion of M. urophthalmus.
... Among the fish orders with representatives in both Am and To-Ar basins, the Osteoglossiformes is one of the first three sister lineages to all other modern teleosts (Greenwood et al. 1966, Arratia 1999, Near et al. 2012, Hilton and Lavoué 2018 and living forms are restricted to freshwater (Myers 1949). Osteoglossiformes species are naturally distributed or introduced to all continents, with the exception of Antarctica (Adite et al. 2005, Nelson et al. 2016, Hilton and Lavoué 2018. ...
The Neotropical region exhibits the greatest worldwide diversity and the diversification history of several clades is related to the puzzling geomorphologic and climatic history of this region. The freshwater Amazon ecoregion contains the main hydrographic basins of the Neotropical region that are highly dendritic and ecologically diverse. It contains a rich and endemic fish fauna, including one of its most iconic and economically important representatives, the bony‐tongue Arapaima gigas (Teleostei, Osteoglossiformes). Here, we evaluated the projected distribution of the genus in different historical periods (Present, Last Glacial Maximum, Last Interglacial Maximum and Near Future) and interpreted these results in light of the genomic diversity and modeled historical demography. For that, we combined species distribution models, population genetic analysis using SNPs and deep learning model selection. We analyzed a representative sample of the genus from the two basins where it naturally occurs, four localities in the Amazon (Am) and three in the Tocantins‐Araguaia (To‐Ar) basin, as well as individuals from three fish farms. We inferred a potentially smaller distribution in the glacial period, with a possible refuge in central Am. Our genetic data agrees with this result, suggesting a higher level of genetic diversity in the Am basin, compared to that observed in To‐Ar. Our deep learning model comparison indicated that the To‐Ar basin was colonized by the population from the Am basin. Considering a global warming scenario in the near future, A. gigas could reach an even larger range, especially if anthropogenic related dispersal occurs, potentially invading new areas and impacting their communities.
... Les poissons d'eau douce vrais sont composés de familles strictement inféodées aux eaux douces car hautement intolérantes à l'eau salée (poissons primaires) et de familles confinées aux eaux douces mais relativement tolérantes à l'eau salée, du moins pour de courtes périodes (poissons secondaires) (Myers, 1949a). Ces dernières sont donc capables de franchir de courtes barrières océanes pour rejoindre un autre bassin. ...
Les poissons migrateurs amphihalins évoluent dans un environnement qui est perturbé, à l'échelle globale, par le changement climatique et à l'échelle régionale, par les pressions anthropiques telles que les barrages et la pollution des cours d'eau. Cette étude, menée à l'échelle continentale, avait pour objectif d'évaluer, de comprendre et de prédire les impacts de changements globaux sur la distribution de ce groupe. Afin de répondre à cette problématique, des modèles empiriques de distribution ont été construits pour chacune des 28 espèces étudiées. Leurs distributions ont été décrites au début et à la fin du XXème siècle, en termes de présence-absence et de classes d'abondance. Les variables explicatives potentielles étaient de type physique, climatique, biotique et anthropique. Dans un premier temps, il a été mis en évidence que la répartition vers 1900 des poissons migrateurs amphihalins était fortement contrainte par leur histoire biogéographique et par les conditions thermiques et hydrauliques de l'habitat continental. La projection de ces distributions, à la fin du XXIème siècle, dans le contexte du changement climatique, a montré la forte sensibilité de ce groupe aux modifications du climat. Bien que spécifiques à chaque espèce, les réponses ont pu être classées en trois catégories : expansion de l'aire de répartition, contraction de l'aire de répartition et peu ou pas de changement. Dans un deuxième temps, pour la première fois à l'échelle continentale, l'importance des grands barrages et de la densité de populations humaines pour expliquer la distribution actuelle de ces espèces a été démontrée. Les relations sont apparues complexes et dépendantes des caractéristiques écologiques des espèces, notamment de la position de leurs habitats de croissance et de reproduction le long du réseau hydrographique et de leur place au sein du réseau trophique.
... Sub-basin specific databases were constructed using historical (pre-1980 to 2018) FWF collection information. The presence of only primary and secondary species (FWF with little or no tolerance to ocean salinity) [26] collected in sites located in each of the Pánuco sub-basins was included in the database. Databases were populated primarily from data in FISHNET2 [27] and the Global Biodiversity Information Facility [28]. ...
Species introductions and extirpations are key aspects of aquatic ecosystem change that need to be examined at large geographic and temporal scales. The Pánuco Basin (Eastern Mexico) has high ichthyological diversity and ecological heterogeneity. However, freshwater fish (FWF) introductions and extirpations since the mid-1900s have modified species range and distribution. We examine changes in FWF species composition in and among four sub-basins of the Pánuco by comparing fish collection records pre-1980 to 2018. Currently, the FWF of the Pánuco includes 95 species. Fishes in the Poeciliidae, Cyprinidae, and Cichlidae, respectively, comprised most records over time. Significant differences in species composition were found between the first (pre-1980) and last (2011–2018) study periods, but not for periods in-between. Eight independent species groups were key for explaining changes in Pánuco river ichthyofauna; one group was dominated by invasive species, and saw increases in the number of records across study periods (faunal homogenization). Another group was formed by species with conservation concern with a declining number of records over time. Thirteen (2 native and 11 non-native) species were responsible for temporal turnover. These results strongly suggest high rates of differentiation over time (via native species loss) following widespread non-native species introductions.
Graphical abstract Highlights d The expanded Panama Canal is currently experiencing a major biotic reconfiguration d The former freshwater fish community is now replaced by a marine one d Large marine fish predators are changing the food web of this tropical system d The exceptional changes increase chances of interoceanic migrations in the Americas
Paleoecological studies have been largely explored in the last decades, providing important data regarding, among other features, the feeding behavior and living environments of extinct taxa. The fish assemblage of the Açu Formation (?Aptian–Cenomanian), Potiguar Basin, has been recently discovered and described, but ecological inferences have not been made. Here, we analyze the known taxa through a multiproxy approach in order to characterize their autecology as well as provide interpretations of these data in the context of the unit. We conclude that the fishes from the Açu Formation were mainly generalists regarding feeding behavior and swimming adaptations, living in different portions of the estuarine system previously inferred for the locality. Comparisons with Western Gondwana units of similar age hint at a great paleontological potential for the unit. The study also highlights the importance of multiproxy approaches in paleoecological studies and the need of a major review on ecological terminology used in them.
The development of unconventional oil and gas shales using hydraulic fracturing and directional drilling is currently a focal point of energy and climate change discussions. While this technology has provided access to substantial reserves of oil and gas, the need for large quantities of water, emissions, and infrastructure raises concerns over the environmental impacts. Written by an international consortium of experts, this book provides a comprehensive overview of the extraction from unconventional reservoirs, providing clear explanations of the technology and processes involved. Each chapter is devoted to different aspects including global reserves, the status of their development and regulatory framework, water management and contamination, air quality, earthquakes, radioactivity, isotope geochemistry, microbiology, and climate change. Case studies present baseline studies, water monitoring efforts and habitat destruction. This book is accessible to a wide audience, from academics to industry professionals and policy makers interested in environmental pollution and petroleum exploration.
Aim: Unravelling the ecological and historical factors that underlie species distributions has challenged ecologists for a long time. Thus, our objective is to understand the role of environmental variables explaining the distribution of three major eco-evolutionary groups of inland fishes (Darlington's divisions: primary, i.e. strict freshwater ; secondary, i.e. salt-tolerant; and peripheral, i.e. diadromous and marine origin), and how these variables are related to fish traits. Location: Iberian Peninsula. Taxon: 51 native and 17 alien inland fish species from the Iberian Peninsula.
Methods: We modelled distributions of the most common inland fish species across the Iberian Peninsula to compare the importance of different predictors among the three Darlington's divisions and between native and alien species. To explore the importance of specific environmental variables in determining the distribution of different traits of inland fish, variable importances obtained from species distribution models were subjected to a redundancy analysis.
Results: Darlington's divisions differ significantly in salinity tolerance, in distribution overlap, in the importance of distribution predictors and associated life-history traits. Topographic and climatic variables were generally more important than land use and anthropogenic factors in explaining fish distributions. We found significant differences in the importance of variables explaining the distribution of native vs. alien species and especially among Darlington's divisions. River basin was most important for primary native and many alien species. Increasing mean temperature and damming were positively associated with the presence of tolerant, large-bodied and warm-water alien species from more hydrologically stable habitats.
Main conclusions: Despite marked differences in the distribution patterns of native and alien species, evolutionary and introduction histories as well as seawater tolerance are central factors explaining the current distribution of inland fishes. Darlington's divisions proved useful for addressing ecological and biogeographical questions at broader spatial scales.
To accurately identify the species that make up the assemblage of the family Cichlidae in the Mexican state of Chiapas, we first updated the total species account (36 species) for the state and then created an identification key. For the distribution maps, the geographic records were projected using a geographic information system considering the layers of the two largest basins in the state (Grijalva and Usumacinta) and the Chiapas coast basin. The dichotomous key includes meristic, morphometric and coloration patterns that facilitate species identification present in the state. Rheoheros coeruleus (Stawikowski and Werner 1987) and Vieja breidohri Werner and Stawikowski 1987 are included in a key for the first time. The distributions of Paraneetroplus gibbiceps Steindachner 1864a, Rheoheros coeruleus, and Vieja zonata Meek 1905 in the state are mapped for the first time, and the range of 16 species was expanded. By updating and creating tools of great
taxonomic use, we contribute to the study of this complex family with high morphological diversity.
RESUMEN El guapote juvenil (Dormitator latifrons) presenta un porcentaje de supervivencia muy elevado al ser transferido directamente a diferentes concentraciones de agua dulce, al agua de mar (AD-AM), lo cual demuestra que el mismo es capaz de hipoosmorregular desde etapas muy tempranas de su ciclo de vida. El estudio de la tasa de agua perdida (T AP, mg/día) a diferentes concentraciones AD:AM (V:V) de 0%, 50%, 75%, 100%; demostró que el guapote juvenil muestra fase de crisis solamente cuando la concentración fue de 100%. Esta última, describe un comportamiento similar al del pez adulto, · lo que indica el carácter anfiádromo del guapote, toda vez que es capaz de emigrar desde y hacia medios marinos durante todo su ciclo de vida.
El Caño Manamo es uno de los tres principales cauces de agua del delta del río Orinoco y es el brazo más septentrional y limítrofe del mismo. El delta del Orinoco puede considerarse todavía como un área incógnita desde el punto de vista ictiológico, por eso es necesario evaluar la estructura de la comunidad íctica continental del caño en cuestión. Para ello se establecieron 9 zonas de muestreo, empleándose para la colecta un tren de arrastre playero de 100 m de longitud x 5 m de alto, con diámetros de malla de 1 y 1/2 pulgadas en los extremos y 1/4 en el centro. Los organismos capturados fueron colocados en bolsas plásticas y refrigerados para su posterior identificación hasta la categoría de especie, utilizando claves taxonómicas especializadas. En total se capturaron 3197 individuos representados en 10 órdenes, 31 familias, 72 géneros y 92 especies. Por zonas de muestreo obtuvieron 30, 29, 21, 22, 26, 35, 26, 30 y 59 especies, para las estaciones: INIA, El Moriche, El Garcero, Caño Iglesia, Boca de Uracoa, Chaguaramas, San Rafael, San Salvador y Los Pinos, respectivamente siendo Aphanotorulus ammophilus, Lycengraulis batesii, Pachypops fourcroi, Psectrogaster ciliata y Triportheus auritus especies comunes en todas las zonas de muestreo. Los Ordenes con mayor número de familias fueron: Characiformes (10) y Siluriformes (8), y las familias más importante tomando en consideración la cantidad géneros fueron: Loricariidae (9), Characidae (6), Pimelodidae (6) y Engraulidae (5). Los géneros más representativos fueron: Serrasalmus (5) y Triportheus, Hypophthalmus y Curimata con 3 especies cada uno. Las mayores abundancias fueron observadas en: Geophagus abalios, Triportheus auritus y Pachypops fourcroi (525, 497 y 207 individuos, respectivamente). Existieron diferencias significativas de las variables ambientales medidas entre los meses de muestreo en la zona alta del delta del río Orinoco. En promedio las variables ambientales fueron: temperatura del agua con 29,69±1,14 ºC, salinidad con 0,01±0,03, conductividad con 51,92±23,97 μS/cm, oxígeno disuelto con 3,24±1,39 mg/l, transparencia del agua de 47,45±28,86 cm, pH de 7,09±0,80. Por otra parte, la abundancia promedio fue de 54,19±50,76 individuos, la riqueza de 9,91±5,25 especies, la diversidad de 2,47±0,73 bit/ind, y la equidad de 0,77±0,16. La mayoría de las especies recolectadas fueron de hábitos accidentales u ocasionales. El modelo matemático que mejor explica como las variables ambientales influyeron en las abundancias de las especies presentes en la zona alta del caño Manamo fue: Modelo= conductividad+salinidad+temperatura+pH+transparencia. Los resultados de este trabajo de investigación son un valioso punto de partida en la generación de conocimientos que permitan promover el aprovechamiento sustentable de la comunidad íctica continental del caño Manamo en el delta del río Orinoco. Además, se muestra que este ecosistema, a pesar de las alteraciones antropogénicas, se mantiene relativamente en equilibrio, debido al alto número de especies que presenta.
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