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Two new Amazonian species of Ancistrus with vestigial adipose fin, with an appraisal on adipose fin loss in neotropical armoured catfishes (Teleostei: Loricariidae)
Abstract
Two new species of Ancistrus are described from Amazon basin: A. krenakarore from rio Itapacura, a tributary of the right margin of the lower rio Tapajós drainage; and A. karajas from small headwater streams of rio Parauape- bas, a tributary of left margin of lower rio Tocantins drainage, both from Para State, Brazil. The two new species differ from all congeners except A. jataiensis, A. parecis, A. reisi, A. tolima, A. tombador, A. verecundus and A. veri- caucanus by the absense or vestigial adipose fin (vs. presence of a fully-developed fin). The new species differ from all congeners without adipose fin by the presence of only one preadipose plate and by a combination of morphometric characters; and differ from each other by color pattern.
This study aims to provide an annotated list of the type-material housed in the fish collection of the Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura (NUP), Universidade Estadual de Maringá, Paraná, Brazil. NUP’s fish type collection hosts type-material of 157 species, distributed in 503 lots (11 holotypes and 492 lots of paratypes) totalling 2,915 specimens. For each species, catalog numbers of all available lots are provided, and for each lot, total number of specimens, range of variation of standard length, number of cleared and stained specimens (when any), locality data, collectors, and date of collection, are provided.
A new Ancistrus species is described from Tapajós and Xingu river basins. It is distinguished from its congeners by the singular body color pattern, consisting of dark vermiculated stripes almost all over the body, and also by combination of features as a narrow head, large internostril distance, and absence of rows of enlarged odontodes on the lateral plates. In addition, the new species is distinguished from congeners that inhabit the rio Tapajós basin by the presence of a fully-developed adipose fin (vs. adipose fin absent in Ancistrus parecis and A. tombador, and vestigial adipose fin or absent in A. krenakarore). It differs from A. ranunculus, also from the rio Xingu, by the color pattern, smaller body size, smaller gill opening, and narrower cleithral width. The new taxon adds a new record to the list of species shared among the Xingu and Tapajós basins.
Numerous rivers, interrupted by large waterfalls and extensive rapids, drain the geologically ancient Guiana Shield Highlands. We describe a new armoured catfish genus and two new species endemic to the upper Ireng and Kuribrong rivers, respective tributaries of the Amazon and Essequibo basins in western Guyana. Corymbophanes ameliae sp. nov. is distinguished by having vermiculations on the abdomen, bands on the caudal fin, the anal fin i,5 and narrow caudal peduncle. Yaluwak primus gen. & sp. nov. is distinguished by having evertible cheek odontodes, a plated snout, a tall caudal peduncle and absence of adipose fin and iris operculum. We present a new molecular phylogenetic analysis inclusive of these and several related genera that suggests that the Corymbophanes clade (Araichthys, Corymbophanes, Cryptancistrus, Guyanancistrus, Hopliancistrus and Yaluwak) originated in the Guiana Shield with secondary dispersal to the Brazilian Shield. Within the Guiana Shield, relationships among Corymbophanes and Yaluwak are consistent with geodispersal between drainages via headwater capture, although an uplift-mediated relictual distribution cannot be ruled out. ND2 haplotype structure among C. ameliae populations suggests that ichthyofaunal diversity on the Guiana Shield escarpment is shaped not only by inter-, but also intrafluvial barriers to gene flow.
During the Mosaico do Apuí expedition in 2006, a new species of Ancistrus was found in the rio Sucunduri, a large tributary of the rio Madeira basin in south Amazonas State. The new species has a unique color pattern for the genus and is distinguished by the presence of alternate light and dark vertical bars on the trunk. Other Ancistrini genera have species with a similar color pattern, but the new species is clearly distinguished by a lack of plates on the snout and presence of fleshy tentacles on the snout as in all Ancistrus representatives. We also provide comments on the taxonomic status of the A. bolivianus, A. heterorhynchus and A. marcapatae.
Construction of water diversions is a common response to the increasing demands for freshwater, ofte resulting in benefits to communities but with the risk of multiple environmental, economic, and social impacts. Water-diversion projects can favor massive introductions and accelerate biotic homogenization. This study provides empirical evidence on the consequences of a proposed law intended to divert water from two large and historically isolated river basins in Brazil: Tocantins to São Francisco. Compositional similarity (CS) and b-diversity were quantified encompassing aquatic organisms: mollusks, zooplankton, crustaceans, insects, fishes, amphibians, reptiles, mammals, and plants. For CS we (i) considered only native species, and (ii) simulated the introduction of non-natives and assumed the extinction of threatened species due to this water-diversion project. We highlight the environmental risks of such large-scale projects, which are expected to cause impacts on biodiversity linked to bioinvasion and homogenization, and we recommend alternatives in order to solve water-demand conflicts.
The fishes herein included were collected in four small streams of the upper rio Tapajós basin. Through fieldwork carried out in 2011, 2013 and 2014 during the low water season 1.728 specimens belonging to 22 species distributed in 11 families, and five orders were captured. Characidae was the most representative family both in number of species and specimens captured. The most abundant species were Hyphessobrycon melanostichos, H. hexastichos, and H. notidanos. Five species are recognized as new, and four as endemic to the upper rio Tapajós basin. This study represents the first fish inventory for the region and will provide valuable information for the conservation of the poorly known diversity of fishes of the Chapada dos Parecis, in the headwaters of the upper rio Tapajós basin. © 2016, Universidade Estadual de Campinas UNICAMP. All rights reserved.
A new species, Ancistrus falconensis, is described from the Hueque and Ricoa Rivers, small, isolated Caribbean drainages of northwest Falcón state, (Western Caribbean Zoogeographic Province) Venezuela and compared with A. gymnorhynchus Kner 1854 which occurs in adjacent drainages to the south. Adults of Ancistrus falconensis usually have small light spots on the abdomen in preserved specimens whereas A. gymnorhynchus almost always has the abdomen uniformly gray). They are further distinguished by the following ratios in specimens greater than 60 mm SL: mouth width/pectoral spine length (0.661–0.915 vs. 0.480–0.669, (two specimens of 88 overlap), dentary tooth cup length/ pectoral spine length (0.207–0.264 vs. 0.143–0.198), and premaxillary tooth cup length/pectoral spine length (0.146– 0.215 vs. 0.215–0.318). Falcón state is arid in the area of the type locality of A. falconensis, and water resources face increasing demands for urban, agricultural and industrial uses. Deforestation, river channelization and water diversion heavily impact most coastal streams, causing accelerating habitat loss and degradation. Thus, this new species must be considered vulnerable to extinction.
Three new species of Ancistrus are described: Ancistrus tombador sp. n. from the upper rio Tapajós basin, and Ancistrus reisi sp. n. and Ancistrus jataiensis sp. n. from the upper rio Tocantins basin. The three species differ from their congeners by the absence of an adipose fin. Loss of the adipose fin was only rarely observed in Ancistrini. In the three new species it is replaced by a series of small unpaired platelets forming a low crest. Ancistrus tombador further differs from all congeners by a unique combination of characters: naked margin of snout large and tentacles usually absent in both sexes; body very narrow (cleithral width 27.5-31.2% SL); long caudal peduncle particularly depressed (depth 8.3-9.2% SL). Ancistrus reisi is distinguished from A. jataiensis by measurements, including: predorsal length (respectively: 43.8-46.4% SL versus 47.5-49.3% SL); occipital depth (14.9-17.0% SL versus 17.0-19.5% SL); and caudal peduncle length (27.7-30.9% SL, versus 24.6-27.1% SL).
The Neotropical catfish family Loricariidae is the fifth most species-rich vertebrate family on Earth, with over 800 valid species. The Hypostominae is its most species-rich, geographically widespread, and ecomorphologically diverse subfamily. Here, we provide a comprehensive molecular phylogenetic reappraisal of genus-level relationships in the Hypostominae, based on our sequencing and analysis of two mitochondrial and three nuclear loci (4293 bp total). Our most striking large-scale systematic discovery was that the tribe Hypostomini, which has traditionally been recognized as sister to tribe Ancistrini based on morphological data, was nested within Ancistrini. This required recognition of seven additional tribe-level clades: the Chaetostoma Clade, the Pseudancistrus Clade, the Lithoxus Clade, the 'Pseudancistrus' Clade, the Acanthicus Clade, the Hemiancistrus Clade, and the Peckoltia Clade. Results of our analysis, which included type- and non-type species for every valid genus in Hypostominae, support the reevaluation and restriction of several historically problematic genera, including Baryancistrus, Cordylancistrus, Hemiancistrus, and Peckoltia. Much of the deep lineage diversity in Hypostominae is restricted to Guiana Shield and northern Andean drainages, with three tribe-level clades still largely restricted to the Guiana Shield. Of the six geographically widespread clades, a paraphyletic assemblage of three contain lineages restricted to drainages west of the Andes Mountains, suggesting that early diversification of the Hypostominae predated the late Miocene surge in Andean uplift. Our results also highlight examples of trophic ecological diversification and convergence in the Loricariidae, including support for three independent origins of highly similar and globally unique morphological specializations for eating wood.
A new small Loricariidae, Hypostomus careopinnatus, is described from the Rio Taquari drainage, upper Rio Paraguay basin, Mato Grosso, Brazil. The new species can be easily distinguished from all congeners, except Hypostomus levis, by the absence of adipose fin. Hypostomus careopinnatus is distinguished from H. levis mainly by the presence of slender bifid teeth, with mesial cusp large and rounded, and lateral cusp small and pointed (vs. spoon-shaped teeth). The new species described herein completely lacks the adipose fin and also lacks the median pre-adipose plates in almost all specimens examined. The absence of adipose fin is probably an independent acquisition for Hypostomus careopinnatus and Hypostomus levis. Um pequeno novo Loricariidae, Hypostomus careopinnatus, é descrito das drenagens do Rio Taquari, bacia do alto Rio Paraguai, Mato Grosso, Brasil. A nova espécie distingue-se facilmente de todas as demais congêneres, exceto de Hypostomus levis, pela ausência da nadadeira adiposa. Hypostomus careopinnatus distingue-se de H. levis pela presença de dentes delgados e bicuspidados, com a cúspide mesial maior e arredondada, e a cúspide lateral menor e afilada (vs. dentes em forma de colher). A nova espécie aqui descrita não possui nadadeira adiposa, e também perdeu as placas medianas pré-adiposa, na maioria dos exemplares examinados. A ausência da nadadeira adiposa é provavelmente uma aquisição independente para Hypostomus careopinnatus e Hypostomus levis.
Populations of seven Ancistrus species were analyzed from streams and rivers of three hydrographic Brazilian basins. All populations showed different diploid numbers (2n), fundamental numbers (FNs), and karyotypes. Some representatives of Loricariidae have 2n = 54 chromosomes, which is very likely an ancestral cytotaxonomic characteristic, but many other representatives show extensive karyotype diversification. In the Ancistrus species studied, extensive karyotypic differentiation, which is generally associated with chromosome number reduction and rearrangement of the ribosomal RNA gene (rDNA) sites, was verified. Chromosomal locations of 18S and 5S rDNA were jointly detected using fluorescence in situ hybridization (FISH). In all the Ancistrus species analyzed, 18S rDNA sites were detected only on one chromosome pair, though this differed among species. 5S rDNA was located on 1-3 chromosome pairs either separately or in synteny with 18S rDNA in four of the seven species/populations. Hence the karyotype differentiation in Ancistrus species could be associated with a morphological speciation process, suggesting that chromosome fusions, inversions, deletions, duplications, and heterochromatination could contribute to the karyotype evolution of these neotropical armored catfishes.
In this study, we describe three new species of the genus Neoplecostomus: N. bandeirante, from Salesópolis in the state of São Paulo, N. langeanii from Muzambinho, in the state of Minas Gerais, and N. botucatu from Botucatu, in the state of São Paulo. All of the described species are found in the Upper Rio Paraná basin. The new species are different from each other and from their nominal congeners in their mitochondrial DNA sequences (COI), morphology and meristic traits, in addition to their color patterns. Morphologically, N. bandeirantecan be distinguished from all congeners by the presence
of moderate keels throughout the lateral series of plates and by a naked area between each mid-ventral and ventral plate that is greater in size than the length of these plates. Neoplecostomus botucatu is morphologically distinguished by a reduction of the adipose fin and the presence of dark spots that are distributed along the body. Neoplecostomus langeanii can be morphologically distinguished by the absence of hypertrophied odontodes and a swollen integument on the head, as well as by morphometric characteristics.
Foram realizadas análises citogenéticas de 117 espécimes do gênero
Ancistrus de três bacias hidrográficas do estado de
Mato Grosso: Paraguai, Araguaia-Tocantins e Amazônica, utilizando as técnicas de
citogenética convencional para obtenção de cromossomos mitóticos,
visualização de regiões heterocromáticas e regiões
organizadoras de nucléolos. Os cromossomos pareados revelaram uma
variação no número diploide de 2n = 40 a 2n = 54 e número
fundamental de NF = 80 a NF = 86. As regiões organizadoras de nucléolos foram
evidenciadas em um único par de cromossomos para todas as espécies e a
heterocromatina é escassa nas espécies com números diploides elevados (2n = 50 a
2n = 54). Os blocos heterocromáticos mais evidentes foram observados nos
pares portadores das AgRONs e em cromossomos da espécie com 2n = 40. Estes dados
contribuem para a hipótese de redução do número diploide nas
espécies que apresentam polimorfismos cromossômicos e cromossomos sexuais, além
de contribuir para inferências sobre os mecanismos de evolução
cariotípica que favoreceu a diversificação do gênero
Ancistrus, o mais representativo na tribo Ancistrini.
Two new species of loricariid catfishes, Parotocinclus bidentatus and P. muriaensis, are described from the rio Paraíba do Sul basin. They possess accessory unicuspid teeth located internally to the series of bicuspid teeth in premaxillary and dentary bones. According to a parsimony analysis of phylogenetic relationships among the Hypoptopomatinae, the new taxa are members of the genus Parotocinclus, even though they lack a fully developed adipose fin. They differ from most species of Parotocinclus because they have accessory teeth. Within the Hypoptopomatinae, accessory teeth are also found only in P. collinsae and members of the genera Eurycheilichtys, Epactionotus and Niobichthys. Duas novas espécies de cascudinhos loricariídeos, Parotocinclus bidentatus e P. muriaensis, são descritas da bacia do Rio Paraíba do Sul. Elas possuem dentes unicúspides localizados internamente à série de dentes bicúspides dos ossos pré-maxilar e dentário. De acordo com uma análise de parcimônia das relações filogenéticas entre os Hypoptopomatinae, as novas espécies pertencem ao gênero Parotocinclus, apesar de não possuírem a nadadeira adiposa plenamente desenvolvida. Elas diferem da maioria das espécies de Parotocinclus pela presença de dentes acessórios. Entre os Hypoptopomatinae dentes acessórios ocorrem apenas em P. collinsae e membros dos gêneros Eurycheilichthys, Epactionotus e Niobichthys.
Two new species Ancistrus are described: A. verecundus from the upper rio Madeira basin and A. parecis from the upper rio Juruena, rio Tapajós basin, Brazil. The two species differ from all congeners except A. jataiensis, A. reisi, and A. tombador in the absence of an adipose fin which is replaced by a series of median platelets forming a low postdorsal ridge. Ancistrus verecundus is further distinguished from these species, except A. tombador by the broad naked margin of the snout and reduced tentacle development. Ancistrus verecundus differs from A. tombador in various morphometric features, and in having the base of the first anal-fin pterygiophore covered by skin (vs. base of the first anal-fin pterygiophore exposed and forming a platelet-like element). Ancistrus verecundus and A. tombador have two or more dermal plates of the dorsal plate series between the end of the postdorsal ridge and the origin of the first plate-like procurrent caudal-fin ray, whereas the other species of the genus that lack an adipose fin, including A. parecis, have one or none. Ancistrus parecis is further distinguished from A. tombador and A. verecundus by the presence of tentacles in adults. It also differs from A. tombador in morphometric and meristic features and from A. jataiensis and A. reisi in the length of the mandibular tooth row, the number of teeth on dentary and premaxillary, and the caudal-peduncle depth. A key is provided for the identification of species of Ancistrus lacking an adipose fin.
The small, non-rayed adipose fin is present in eight extant orders of fishes, including the Salmoniformes (salmon and trout)
but the functional significance of the trait is unknown. Recent evidence suggests a hydrodynamic function in juvenile salmonids,
and observations of sexually dimorphic adipose fin expression and female preference for males with large fins indicate a role
in reproduction by mature individuals. To the extent that the adipose fin functions in reproduction, it might be expected
to evolve in parallel with other sexually dimorphic traits, such as body depth and jaw length. To test this hypothesis, we
quantified adipose fin size of mature male sockeye salmon, Oncorhynchus nerka, among five populations. Populations differed significantly in adipose fin size after correcting for variation in body length
and body depth. Adipose fin size tended to parallel the development of other secondary sexual characteristics, but was more
closely related to body length and body depth than jaw length. Interestingly, shallow bodied populations from small creeks
with high brown bear, Ursus arctos, predation during spawning tended to have smaller size-adjusted adipose fins than populations spawning in deeper water. However,
it remains unclear whether adipose fin size is being selected independently of other traits or if it is pleoitropically linked
to a trait under selection (e.g., body size or shape).
This study reports on the importance of the size of the kype (lower jaw) and the adipose fin for establishing and maintaining social dominance in pair-wise interactions among size-matched, reproductively active male Arctic charr Salvelinus alpinus. The size of these traits seems not to have a large influence on establishing dominance, but after 4 days of social interactions, and after dominance rank is established, subordinate males show reduced size of their adipose fins and kypes relative to that of dominant males. Consequently, these traits seem to be costly labile characters that could be of importance in inter and intra-sexual evaluations of individual quality.
Loricariid catfishes show a predominance of homomorphism in sex chromosomes, but cases of simple and multiple systems were also found. Here we describe two cases of multiple sex chromosome systems in loricariids from Brazilian Amazonia. Males of Ancistrus sp.1 "Balbina" have a modal number of 2n = 39 chromosomes, fundamental number (FN) of 78, and karyotypic formula of 27 m + 10 sm + 2 st; females have 2n = 38 chromosomes, FN = 76, and 26 m + 10 sm + 2 st. Ancistrus sp.2 "Barcelos" has 2n = 52 chromosomes for both sexes, FN = 80 for males and FN = 79 for females. Karyotypic formula is 12 m + 12 sm + 4 st + 24a for males and 11 m + 12 sm + 4st + 25a for females. The two species show different arrangements of constitutive heterochromatin blocks, which are coincident with NORs and absent in sex chromosomes. We suggest a XX/XY(1)Y(2) mechanism for Ancistrus sp.1 "Balbina", and a Z(1)Z(1)Z(2)Z(2)/Z(1)Z(2)W(1)W(2) mechanism for Ancistrus sp.2 "Barcelos". The XX/XY(1)Y(2) mechanism here reported is the second known occurrence of this type of multiple sex chromosomes for Loricariidae and the third for Neotropical fishes; the mechanism Z(1)Z(1)Z(2)Z(2)/Z(1)Z(2)W(1)W(2) represents the first record among fishes. The presence of different sex chromosome systems in Ancistrus indicates a probable independent origin and suggests that the differentiation of sex chromosomes is evolutionarily recent among species in this genus.
Neoplecostomus paranensis was the only Neoplecostomus species known from the upper Rio Paraná basin, and it was diagnosed from its congeners mainly by the absence or reduction of the adipose fin. In this study we describe three new Neoplecostomus species. All of them are promptly differentiated from N. paranensis by having a well-developed adipose fin. Furthermore, the new species are differentiated from congeners by morphometric and meristic traits, in addition to color pattern. Neoplecostomus paranensis is redescribed. We also provide an identification key to all Neoplecostomus species.
The genus Otocinclus Cope (1872) of the siluriform family Loricariidae is diagnosed as monophyletic on the basis of shared derived characters of the cranial and hyobranchial skeleton, dorsal gill arch musculature, and gut. Otocinclus are relatively small herbivorous catfishes restricted to small streams and quiet slow-flowing margins of larger rivers, most frequently living in close association with aquatic macrophytes and terrestrial marginal grasses extending into the water column. Otocinclus species share a novel modification of the distal esophageal wall which is developed into an accessory blind diverticulum that may function in aerial respiration and for providing additional modulatory positive buoyancy for remaining in the upper water column at stream margins. Otocinclus has no junior synonyms, however several nominal species originally described in Otocinclus are here formally re-assigned to other genera in the subfamily Hypoptopomatinae. Otocinclus cephalacanthus Ribeiro 1911, O. depressicauda Ribeiro 1918, O. francirochai Ihering 1928, O. laevior Cope 1894, O. leptochilus Cope 1894, O. maculipinnis Regan 1904, O. nigricauda Boulenger 1891, and O. paulinus Regan 1908 are all placed in the genus Microlepidogaster Eigenmann & Eigenmann 1889; O. obtusos Ribeiro 1911 was placed in Pseudotothyris Britski & Garavello 1984; the genus Nannoptopoma Schaefer 1996 was erected for O. spectabilis Eigenmann 1914 in the tribe Hypoptopomatini; O. gibbosus Ribeiro 1908 is removed from Otocinclus, yet remains of undetermined generic status. Thirteen species are recognized in Otocinclus: O. affinis Steindachner 1877 of the lower Paraná/Paraguay and Uruguay basins and coastal streams of southeastern Brazil; O. bororo n. sp. of the upper Río Paraguay; O. caxarari n. sp. of the middle Río Guaporé/Mamoré system; O. flexilis Cope 1894 of the lower Paraná/Paraguay and Uruguay basins and coastal streams of southeastern Brazil; O. hasemani Steindachner 1915 of northern Brazil; O. hoppei Ribeiro 1939 of the upper Amazon, Tocantins and Paraguay basins and coastal streams of northeastern Brazil; O. huaorani n. sp. of the upper Amazon and Orinoco basins; O. macrospilus Eigenmann & Allen 1942 of the upper Amazon basin of Colombia, Ecuador, and Peru; O. mariae Fowler 1940 of the lower Amazon, upper Madeira and Paraguay basins; O. mura n. sp. of the middle Amazon River; O. vestitus Cope 1872 of the upper Amazon and lower Paraná basins; O. vittatus Regan 1904 of the Amazon, Orinoco, Paraná/Paraguay, and Tocantins basins; and O. xakriaba n. sp. of the rio São Fransisco basin. Two species are placed in synonymy: Otocinclus arnoldi Regan 1909 and O. fimbriatus Cope 1894 are junior synonyms of O. flexilis. Keys to the species of Otocinclus and genera of the Hypoptopomatinae are provided. A descriptive treatment of the osteology and cranial myology is provided for O. vittatus. Detailed analysis of meristic and morphometric variation based on geometric morphometric procedures is provided for the phenetically similar species pairs O. mariae and O. vittatus, O. bororo and O. huaorani in an a posteriori evaluation of separate species status. The phylogenetic relationships among Otocinclus species, and the phylogenetic position of Otocinclus among genera of the Hypoptopomatinae, are determined based on analysis of 27 morphological features using cladistic parsimony. Monophyly of Otocinclus was confirmed; within Otocinclus, a clade comprised of O. affinis and O. flexilis is the sister-group to the remainder of the genus. Within that latter clade, O. hasemani and O. xakriaba are the first and second-level sister-groups to the remainder of the genus, within which relationships among species are not fully resolved with available data. The phylogenetic biogeography of Otocinclus is informative regarding the historical relationships among major river drainage basins, particularly of those river systems of the Brazilian Shield. A biogeographic hypothesis is proposed based on the area cladogram derived from the species-level phylogenetic relationships, which suggests successive vicariance and speciation in the non-Amazonian regions of endemism of southeastern and eastern South America, followed by speciation and dispersal within the Amazon, Orinoco and upper Paraguay basins. The pattern of vicariance revealed by the Otocinclus species-level phylogeny is congruent with the geologic history of the major river drainage basins of the Brazilian Shield. This result suggests that, for Otocinclus and perhaps other loricariid catfishes, much of their generic and species-level diversification occurred prior to the formation of the Amazon basin.
Ancistrus maximus, new species, is described from the igarapé Macoari, rio Branco drainage, Roraima State, Brazilian Amazon. It is distinguished from all congeners, except A. dolichopterus, A. fulvus and A. latifrons, by having more branched rays in the dorsal fin (8 vs. 7). Ancistrus maximus is distinguished from A. dolichopterus, A. fulvus and A. latifrons by color pattern and by the combination of various characters. Ancistrus maximus is remarkable in its very large body size, attaining 200 mm SL, an uncommon size for species of the genus reached otherwise only by A. chagresi and A. centrolepis.
Armored catfish (Loricariidae) are the major grazers of attached algae in pools of the Rio Frijoles, Panama (9@?9' N, 79@?44' W). In the dry season, sunny pools were inhabited by @?6 individuals loricariids per square metre of grazeable substratum. At these densities, armored catfish depleted algae and cleared sediment from bedrock substrata, leaving sparse standing crops of small, adnate diatoms (primarily Achnanthes spp.). To study the effects of armored catfish at 1/6 their natural density, I stocked four 6-7 cm (SL), 10-g Ancistrus (the most common size class of the most common species in stream pools) in each of five stream pens. Pens enclosed 4 m^2 of bedrock substratum, and were alternately stocked or left empty during three consecutive periods of 29, 11, and 11 d. At the end of each period, standing crops of sediment and attached algae, and rates of photosynthesis by attached algae, were measured. The attached algae that developed with sparse Ancistrus had higher standing corps with larger cells or colonies, and higher primary productivity, than did periphyton subjected to heavy grazing by unconfined armored catfish. Even heavy grazing, however, was less deleterious to attached algae than prolonged sedimentation on substrata in enclosures left empty for 11 or 29 d. The net effect of Ancistrus on their algal food changed from depletion at high grazer densities to enhancement at low grazer densities, as sedimentation became more limiting to algae than grazing.
The adipose fin on fishes is a highly conserved and enigmatic, small, non-rayed fin that has persisted from the Mesozoic on some basal teleosts such as salmonids. Using juvenile steelhead, Oncorhynchus mykiss (Walbaum, 1792), ranging from 5 to 18 cm standard length, we experimentally test the effects of adipose fin removal on swimming performance in a variable velocity flow chamber and quantify, with seven independent trials, amplitude and frequency of caudal fin movement at multiple flow velocities (range 10-39 cm.s(-1)). Results demonstrate that adipose fin removal on smolts produces an average 8% (range -3% to 23%) increase in caudal fin amplitude relative to unclipped fish across all velocities. However, we observed no effects in trials with smaller fish (<7 cm) or larger fish (>12 cm). Consistent with speculations in the literature, our results show that the adipose fin may function to control vortices enveloping the caudal fin during swimming or, alternatively, function as a passive precaudal sensor of turbulent flow. Phylogenetic persistence of this trait among multiple groups of early bony fishes is probably due to its hydrodynamic attributes rather than developmental constraints, and the current widespread practice in fisheries of removing the adipose fin as a marking technique may have significant biological costs.
Based on recent evidence suggesting a hydrodynamic function of the small adipose fin in salmonids to turbulent flow conditions, we test for associations between presence and absence of the adipose fin and flow regime in Siluriformes, one of the largest freshwater groups of fish with variable expression of this fin. Among 1906 species from multiple families, those living in habitats with flow (streams or rivers) exhibited an adipose fin significantly more frequently than expected relative to no-flow habitats (lakes, marine, parasitic). These trends were robust and occurred on different continents and among multiple paired comparisons within sister groups. Exceptions to these trends generally had atypical body shape or occupied divergent habitat types. These results are concordant with the hydrodynamic function of this small fin.
Armored catfish, Ancistrus spinosus, graze substrates in a central Panamanian stream. They ingest both attached algae and sediment that settles onto substrates. During the dry season, this sediment is organic-rich (18–24% ash-free dry weight), and is derived from decomposing periphyton and vegetation from the surrounding, largely deciduous forest. This sediment, however, is not a food for Ancistrus, and in fact imposes energetic costs. These costs were estimated to be 15–22% of the daily energy budgets of 10 g individuals held under experimental conditions. In the stream, the presence of thick sediment on substrates increases the tendency for small Ancistrus to seek out larger individuals or areas cleared by them. Clearing of substrates by larger individuals may be particularly important to smaller Ancistrus during the dry season, when sediment-free substrate in stream pools is in short supply.
Ancistrus is the most speciose genus of the tribe Ancistrini, with 58 valid species and many yet to be described. Cytogenetic studies were conducted on five apparently undescribed species from the Amazon basin, which showed different diploid numbers: Ancistrus sp. Purus (2n = 34); Ancistrus sp. Macoari (2n = 46); Ancistrus sp. Dimona (2n = 52); Ancistrus sp. Vermelho (2n = 42) and Ancistrus sp. Trombetas (2n = 38). All species possessed only one pair of NOR-carrying chromosomes, but with extensive variation in both the location on the chromosome as well as in the position of the ribosomal sites on the karyotype. The karyotypic evolution of Ancistrus species seems to be based on chromosomal rearrangements, with a tendency to a reduction of the diploid number. Two new instances of XX/XY sex chromosomes for Ancistrus species, based on the heteromorphism in the male karyotype, were also recorded. The large karyotypic diversity among Ancistrus species may be related to biological and behavioural characteristics of these fish that include microhabitat preferences, territoriality and specialized reproductive tactics. These characteristics may lead to a fast rate of fixation of chromosomal mutations and eventually speciation across the basin.
Nekton. Junk, The Hague
- Y G Aleyev
Aleyev, Y. G. 1977. Nekton. Junk, The Hague, vi + 435 pp.
Subfamily Ancistrinae (armored catfishes)
- S Fisch-Muller
Fisch-Muller, S. 2003. Subfamily Ancistrinae (armored
catfishes). Pp. 373-400 in: R. E. Reis, S. O. Kullander & C. J. Ferraris (eds.), Check list of the
freshwater fishes of South and Central America.
Edipucrs, Porto Alegre.
Die Hypostomiden. Zweite Hauptgruppe der Familie der Panzerfische (Loricata vel Goniodontes)
- R Kner
Kner, R. 1854. Die Hypostomiden. Zweite Hauptgruppe der Familie der Panzerfische (Loricata vel Goniodontes). Denkschriften der Kaiserlichen Akademie
der Wissenschaften, 7: 251-286.