A rapidly growing literature shows that COVID-19 and the measures to contain the spread of the virus can have significant market impacts for seafood. These can be interruptions of production, or reductions in demand directly or indirectly due to supply chain challenges. In this paper we investigate the potential impacts of COVID-19 on seafood exports from Norway, the world's second largest seafood exporter, using highly detailed data from 2016 through May 2021. These data allow us to assess upstream impacts in the seafood supply chain close to the producer level in aggregate and by main sector, impacts on the largest products, and the extent to which export firm structure and export markets served have changed. We find very few impacts in aggregate as well as for individual products, suggesting that the markets and supply chains used by Norwegian seafood exports were sufficiently robust and flexible to accommodate the shocks created by COVID-19. Given Norway's size as a seafood exporter, the impact of COVID-19 has likely been moderate upstreams for a number of seafood sectors around the world, especially those in wealthy nations, with opportunities balancing out challenges, and that the supply chains have been highly resilient.
Satellite-linked buoys used by tropical tuna purse-seine vessels on drifting fish aggregating devices (DFADs) provide a continuous stream of information on both the ocean characteristics and the presence and size of fish aggregations associated with DFADs, enabling the study of pelagic communities. This unprecedented amount of data is characterized by ocean-scale coverage with high spatial and temporal resolutions, but also by different data formats and specifications depending on buoy model and brand, as well as on the type of data exchange agreements into play. Their use for scientific and management purposes is therefore critically dependent on the abilities of algorithms to process heterogeneous data formats and resolutions. This paper proposes a unified set of algorithms for processing the buoys location data used by the two major purse seine fleets operating in the Atlantic and Indian oceans. Three main issues that need to be addressed prior to the exploitation of the data are identified (structural errors, data records on land and on-board vessels) and five specific filtering criteria are proposed to improve the data cleaning process and, hence, quality. Different filtering procedures are also compared, and their advantages and limitations are discussed.
Identifying changes in the population structure and dynamics for fish stocks is important to support its management. Data obtained from 1976 to 2019 allowed to follow up long more than four decades the changes in the population structure and life-history of Umbrina canosai, an intensely exploited demersal sciaenid fish in southern Brazil. Intense fishing caused the truncation of the length/age structure with the loss of most of the bigger/older fishes and the sex ratio change, with increasing frequencies of males. A considerable increase in individual growth was observed and attributed to the lower competition for food due to the reduction in the density of the overall coastal benthic-feeding fish community caused by intense fishing. The large increase in the mortality and the exploitation rate resulted in a drastic decrease in the reproductive potential despite some anticipation in the sexual maturation. Despite the adaptative response to intense fishing, the high exploitation rates and the drastic reduction of the spawning potential ratio in recent years, are clear evidences that U. canosai could be reaching its adaptive capacity for resilience. Therefore, an urgent necessity for a drastic reduction of the fishing mortality to avoid the economic collapse of the fishery is required.
The narrow-clawed crayfish (Pontastacus leptodactylus) is one of the most ecologically and economically important freshwater species in Turkey. However, the harvest of this species has declined from 7937 t in 1984 to 696 t in 2019. One of primary reasons for this decrease in stock is the use of fishing gears with poor size selectivity. In this study, new codend designs were investigated to improve the size selectivity of fyke nets for P. leptodactylus. Seven codends of three different designs were tested: (1) a commercially used standard codend with 34 mm mesh size (Com34); (2) sorting grids with 20 (SG20), 25 (SG25) and 30 mm (SG30) bar spacing attached to the last circle of the net; and (3) a stiff rigged net, the last part of the fyke nets (codend) with 34 (SRN34), 42 (SRN42) and 50 mm (SRN50) mesh size. The average length at 50% retention probability (L50) and selection range (SR) (L75–L25) values of Com34 were 9.4 cm and 3.1 cm, respectively. For the SG20, SG25 and SG30 grids, the L50 values were 11.3 cm, 11.6 cm and 12.0 cm, while the SR values were 1.4 cm, 1.3 cm and 0.6 cm, respectively. For the SRN34, SRN42 and SRN50 codends, the L50 values were 10.9 cm, 11.6 cm and 11.6 cm, while the SR values were 2.1 cm, 2.1cm and 1.1 cm, respectively. Overall, the commercial codend resulted in lower L50 values when the minimum conservation reference length of 10 cm was considered. However, all tested new codend designs showed improved selectivity compared with the standard, with optimum results obtained with SG20. SG20 grid decreased discarding by 15.7% compared to the classic commercial fyke net; thus, this is a very important result for the sustainability of natural P. leptodactylus stocks.
Age, growth and maturity of frigate tuna ( Auxis thazard ) were studied for the first time in Southeast Brazil. A total of 650 fish (265–494 mm Fork Length) were sampled from beach-seine landings between March 2018 and February 2019. Sectioned fin spines from 548 specimens were processed and age was determined by counting and measuring of increments. Growth parameters were fitted to length-at-age data using the von Bertalanffy growth function and were compared to the literature using the growth performance index (Phi). Macro and microscopic characterization of gonads and physiological indexes were used for the analysis of the reproductive cycle. The length distribution did not differ by sex. Assigned ages were between 0+ and 4 years, with annual increments formed during winter. Coefficient of variation between readings was 11%. Growth differed by sex, and the von Bertalanffy growth parameters were L ∞ = 471 mm; k = 0.47 year ⁻¹ ; and t 0 = –1.46 year ⁻¹ for females; L ∞ = 498 mm; k = 0.35 year ⁻¹ ; and t 0 = –2.01 year ⁻¹ for males. Phi was 5.0 for both sexes. Estimated growth rate is among the lowest recorded for the species, possibly related to the method used for age and growth assessment. Gonadosomatic index peaked in December, associated with the upwelling of the South Atlantic Central Waters, at a temperature of approximately 16 °C. Spawning activity in colder waters has never been reported for this species and may be influenced by a richer habitat caused by the intrusion of more nutritive rich waters during spring-summer, which allows larval development. Length-at-first-maturity ( L 50 ) was 345.4 mm for females and 329.8 mm for males.
Industrial aquaculture is a dynamic area capable of solving problems of healthy nutrition and food security. Increase of organic pollution, number of opportunistic microorganisms in the aquatic environment of fish farms and the global contamination of feed by mycotoxigenic fungi are serious problems of industrial fish cultivation. The results are weakening of the general condition of fish, immunosuppression, the occurrence of various diseases complicated by drug resistance, the accumulation of antibiotics and chemical compounds in tissues. Probiotics can be an alternative to antibiotics. The use of probiotics is also one of the biological methods for maintaining and restoring the normal physiological state of fish and increasing their productivity. The aim of this review is the scientific justification of the use of lactic acid bacteria as the safest microorganisms in the development of probiotics for aquaculture. The review presented provides criteria for selecting candidate strains for effective probiotics development. The advantages of lactic acid bacteria for the prevention or control of infectious diseases in cultured fish are considered. Lactic acid bacteria are representatives of the fish microbiota, they have antagonistic activity against opportunistic pathogens, fungi and viruses that cause microbiological spoilage of feed, pollute water bodies, and cause diseases of aquatic animals. The review provides information on various researches in which lactic acid bacteria or products derived from them have been used to assess their potential in aquaculture. Numerous scientific studies prove the value of this vast group of microorganisms for the prevention and treatment of fish diseases, for increasing the resistance of aquatic animals to infectious diseases and various stresses, for improving their survival and productivity, and for improving water sanitation in fish reservoirs. Increased use of effective probiotic lactic acid bacteria in aquaculture can make the fish sector safer, more productive and friendly to the environment and human well-being, and will contribute to the sustainable development of aquaculture.
Original fish-farming developments occur in west-central and south-western Côte d’Ivoire and in the forest area of the Republic of Guinea. Oreochromis niloticus and Heterotis niloticus are the main species produced in dam ponds with little or no feeding. Flooded rice is often grown here. The products supply local markets. In this article, we seek to understand the innovation trajectories that have led to three practices characteristic of these systems: ‘large tilapia production with little feed in dam ponds’, ‘tilapia and Heterotis polyculture’ and ‘flooded rice cultivation in ponds’. We then assess the contribution of these innovations to ecological intensification. The practices that form the basis for current developments were developed in the 1990s on family farms. The suitability of technical choices at certain key moments depended entirely on the fish farmers who judged the tested techniques on their own terms. Our assessment shows that these farmers have contributed positively to ecological intensification. They suffer from recurrent cash flow problems and have thus natural resources and ecological functions in their fish farming system: stocking density to make the best use of the natural trophic resources, improved by polyculture and additional rice production that is more efficient than traditional lowland rice production. The promotion of reliance on existing know-how and anchoring in local culture strengthen the contribution to these systems’ ecological intensification. The analysis shows that this development of integrated commercial fish farming in family farms questions ecological intensification and innovation in aquaculture.
Farm escapees and their offspring impose a significant impact on the environment and may therefore alter the future evolutionary trajectories of wild populations. To date, there is no management plan in place in Mediterranean countries to prevent fish escapes. Here, we investigate microsatellite length variations in three candidate genes, including prolactin (PRL), growth hormone (GH), and the receptor activity modifying protein 3 gene (RAMP3), to study the genetic structure of the main fish species farmed in the Mediterranean, gilthead seabream ( Sparus aurata ). We also evaluate the performance of microsatellites in discriminating fish origin (wild or farmed). Results from 298 individuals, including farmed, wild adult and juvenile fish were compared with results from 19 neutral markers used in a previous study. All loci were polymorphic, selectively neutral, and had the statistical power to detect significant population differentiation. Global FST was similar to that estimated using 19 loci (0.019 and 0.023, respectively), while pairwise comparisons identified farmed populations as the main drivers of genetic divergence, with a much higher magnitude of overall genetic differentiation within farmed populations (0.076) than that estimated using the 19 neutral microsatellite loci (0.041). Bayesian structural analysis showed that the PRL, GH, and RAMP3 markers were able to distinguish farmed from wild populations, but were not able to distinguish different wild groups as 19 neutral microsatellite markers did. Farmed populations of different origins were assigned to a separate cluster with a high individual assignment score (>88%). It appears that the candidate markers are more influenced by artificial selection compared to neutral markers. Further validation of their efficiency in discriminating wild, farmed, and mixed fish origins using a more robust sample size is needed to ensure their potential use in an escaped fish monitoring programme.
The widespread usage of nanotechnology in many essential products has raised concerns about 24 the possible release of nanoparticles (NPs) into aquatic habitats. Cerium dioxide (CeO 2) has gained the most 25 interest in the worldwide nanotechnology industry of all types of Ce minerals owing to its beneficial uses in a 26 wide range of industry practices such as catalysts, sunscreens, fuel additives, fuel cells, and biomedicine. 27 Besides, it was realized that CeO 2 nanoparticles (n-CeO 2) have multi-enzyme synthesized properties that 28 create various biological impacts, such as effectively antioxidant towards almost all irritant intracellular 29 reactive oxygen species. Lately, it was discovered that a large amount of n-CeO 2 from untreated industrial 30 waste could be released into the aquatic environment and affect all living organisms. In addition, the 31 physical/chemical characteristics, fate, and bioavailability of nanomaterials in the aquatic environment were 32 discovered to be related to the synthesis technique. Thus, there are intended needs in identifying the optimal 33 technique of synthesized CeO 2 nanoparticles in order to assess their beneficial use or their potential 34 ecotoxicological impacts on aquatic organisms and humans. Therefore, this review sheds light on the 35
Various single leaf meal can substitute costly de-oiled rice bran (DORB) in farm made feed for carps. However, the use of mixed leaf meal (LM) in fish feed is not reported yet. Therefore, Vigna mungo, Ipomoea aquatica and Hygrophila spinosa leaf meals were blended in an equal proportion to prepare LM. DORB was the major energy source in control diet (C) and LM substituted 50% and 100% of DORB in LM20 and LM40 experimental diets, respectively. In addition, control diet (C), LM20 and LM40 diets were supplemented with limiting amino acids and exogenous carbohydrases and denoted as CE, LM20E and LM40E, respectively. Labeo rohita fingerlings were fed till satiation for 60 days. Fish fed with LM20E diet exhibited maximum growth rates and feed conversion (p <0.05) however these were similar in C and LM40 (p> 0.05). Amylase and aminotransferase activities were positively related with growth indices (p< 0.05). Difference in hematological indices was negligible (except total leukocyte count), and lactate dehydrogenase activities in DORB and LM-based fed groups (p> 0.05) while lower superoxide dismutase activities was observed in LM fed groups (p<0.05). The present study concluded that LM up to 400 g kg-1 could be incorporated as complete DORB replacer in L. rohita diet, however, 200 g kg-1 LM supplemented with 0.98 g L-lysine kg-1 and 1 g exogenous enzyme kg-1 registered the best growth, nutrient utilization, feed conversion ratio, physio-metabolic responses and hematological status.
The green tiger prawn Penaeus semisulcatus is one of the major commercial trawl crustaceans in the Red Sea, the Arabian Gulf, and the Indian Ocean. Herein, we aimed to assess its genetic diversity and phylogeographic criteria in the North West (NW) of the Red Sea. Prawn samples were collected from the Bitter Lakes; the North; and the South of the Gulf of Suez in Egypt. The hypervariable, 5´ barcode area of the Cytochrome oxidase subunit 1 (COI) gene was PCR-amplified and sequenced in all samples. The resulting sequences were subjected to several genetic, phylogenetic, and population genetics´ analyses. Consequently, clear signs of genetic populations´ diversity, expansion; and possible structuring were identified in different areas in the NW Red Sea. Furthermore, extremely discordant genetic connectivity was found between the populations around the Arabian Plate (i.e. of the Red Sea and Strait of Hormuz) and the IndoWest Pacific, resulting in characterizing the Arabian plate populations as a separate lineage of P. semisulcatus. Based on these findings, it is important to investigate whether there are other discriminative genomic, morphological and/or morphometric differences among the genetically identified lineages and populations. Consequently, differential conservational strategies of different populations of this species should be applied in the studied areas.
Dwarf oysters in the Ebro Delta are only observed growing on local pen shells, Pinna nobilis L., currently under extinction risk. The species identification of these populations is uncertain, given recent genetic classifications of dwarf oysters of Ostrea stentina species complex. Hence, the first objective of this study was to confirm the identity of dwarf oysters associated to P. nobilis in the Ebro Delta. Then, we aimed to assess the viability of hatchery and nursery production of O. stentina for potential conservation programs using diets based on a mix of live microalgae species or the commercial Shellfish Diet 1800 ® . Our results showed that COI sequences obtained were specific to O. stentina . Significant differences in the growth and survival of larvae between diet treatments were observed in 3 days. For the live diet, the larval period lasted from 15 to 22 days (299.2 ± 4 µm) whereas it took up to 36 days using the Shellfish Diet 1800 ® (280 ± 7.2 µm), with an overall mortality of 72.3 vs. 99.3%, respectively for each diet. Besides, no seed survival was observed for the commercial diet after a 10-day-fixation attempt. In contrast, ca. 16% of the individuals on the live diet that were allowed to settle reached the juvenile stage and could be released to the environment. Histological examination of obtained seed did not present any sign of disease and showed gonadal development for both sexes at ca. 6 months of age (16.1–19.1 mm). The growth curve obtained was fitted to a Schnute-Richards growth model which returned ages of up to 10 years for maximum local sizes of 45 mm. We conclude that although the Shellfish Diet 1800 ® is not an adequate diet for O. stentina , its hatchery production is feasible and might provide support to future conservation actions.
The starry smooth-hound Mustelus asterias is a near-threatened coastal shark in Europe, whose parasitofauna is largely unknown. We studied metazoan parasites of 20 immature sharks (13 males and seven females) from the English Channel and we examined their relationships with host condition and their use as host bioindicators. All the sharks were parasitized by one to six metazoan taxa among the twelve recorded in the whole sampling (one trematode, six cestodes and two nematodes trophically-transmitted; one monogenean, one copepod and one myxosporean on gills), with a mean abundance of 30.5 ± 21.4 parasites per fish (myxosporeans not included). The three major taxa were in decreasing order: the nematode Acanthocheilus rotundatus (prevalence: 75%, Confidence Interval 53–89%), the cestode Eutetrarhynchus sp. (70%, CI 48–85%), and the monogenean Erpocotyle laevis (60%, CI 39–78%). The gill copepod Kroyeria lineata and the gut nematode Proleptus obtusus were identified as significant pathogens. Parasite community differed between males and females despite their immature stage, suggesting early spatial sex-segregation, with E. laevis , Eutetrarhynchus sp. and Anthobothrium sp. proposed as tags. We discuss results in terms of host fitness loss and information given by parasites on diet ecology and stock discrimination. We recommend incorporating parasitology in further research to improve shark conservation and management.
The durability of animal parts that are collected and traded as trophies has an impact on species sustainability, especially when animals are slow-growing, have low fecundity, or are particularly vulnerable to capture. CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora), aims to control the trade of wild fauna and flora specifically by using trade restrictions as a policy option. However, specialists in international trade have advised against using trade restrictions to correct social cost issues. The reasons for this advice have to do with the unintended economic consequences of animals being placed on an endangered species list, coupled with the trade restrictions themselves. We focused on Pristis spp. (sawfish), a species in danger of extinction found in Appendix I of the CITES convention. An extensive search of sawfish saws for sale on the internet was performed during 2016 and 2017. A total of 174 observations of market prices were collected. We estimated several models linking prices to the size of the saw with other variables that might explain price variability using OLS regression, and which included data from both the original internet searches and additional variables, including a dummy variable which indicated the year in which the species group was placed in Appendix I. These models show that rather than slow down the extinction pathway for this species, CITES may have sped it up, as well as driving the sawfish trophy markets underground.
The physiological response of two species of mussels ( Mytilus edulis and M. galloprovincialis ) and two species of oysters ( Crassostrea gigas and Ostrea edulis ) to temperature, oxygen levels and food concentration, factors likely to vary as a result of climate change, was determined experimentally. Bivalves of similar size from different origins were exposed to six temperatures (3, 8, 15, 20, 25 and 30 °C) at two food regimes (2 and 10 μg Chl a L ⁻¹ ) for 6 weeks. In a parallel running experiment M. edulis from the same batches were exposed to three different temperatures (15, 20 and 25 °C) and three different oxygen levels (30, 50 and 100%) at two food regimes (2 and >8 μg Chl a L ⁻¹ ) for 3–4 weeks. Survival during the experiment ranged from 93% to 100% except for the mussels exposed to 30 °C which showed 100% mortality after three to 32 days. Higher food conditions showed higher optimal temperatures for growth of mussels and oysters. In addition, at the high food treatment, reduced O 2 saturation resulted in lower growth of mussels. At the low food treatment there were no differences in growth among the different O 2 levels at the same temperature. At high food concentration treatment, M. edulis growth was higher with low temperature and high oxygen level. Condition index was higher at higher food concentrations and decreased with increasing temperature. In addition, condition was lower at low oxygen saturation. Lower clearance rates were observed at high food concentrations. At 100% saturation of oxygen, mussel clearance rate increased with temperature at High food regime, but not at Low food regime. Mussel clearance rates were significantly reduced with low oxygen concentrations together with high temperature. Oxygen consumption significantly increased with temperature. Oxygen saturation was the main factor affecting mussel clearance rate. High temperature and low oxygen concentration combined significantly reduced clearance rate and increased oxygen consumption. These response curves can be used to improve parameterisation of individual shellfish growth models taking into consideration factors in the context of climate change: temperature, food concentration, oxygen concentration and their interactions. The observation that abiotic factors interact in affecting mussels and oysters is an important result to take into account.
Coryphaena hippurus is a large pelagic species and constitutes an important by-catch in drift gillnet, trolling and long-line fishing gears operated along the Bay of Bengal, northeastern Indian Ocean. The present study, first from the region, is aimed at deciphering the feeding dynamics from 1150 individuals collected from 2017 to 2019. 32.17% of the fishes had empty stomachs or was with food traces, 45.57% had partially-full stomachs and 22.26% had full stomachs. The feeding intensity was inferred through stomach filling and predator-prey weight ratio, which was higher in May and lower in January, and increasing as increase in the fish size. Coryphaena hippurus is considered a piscivorous pelagic predator as pelagic teleosts contribute more than half of the prey species. Major prey species were big-eye scad (27.3%), squid (10.3%), crabs (9.3%), Indian mackerel (7.2%), Indian scad (5.9%), whitebaits (5.7%) and sardines (5.4%). Scads and crabs were abundantly preyed during summer and winter, while clupeids and engraulids in monsoon; however, no significant variations were observed in prey composition between sizes. Trophic Level was 4.22 ± 0.15 and Levins Standardized Niche Breadth Index was 0.30. Dietary niche breadth was higher during summer (0.48) and monsoon (0.33) and in fishes measuring 60.0–74.9 cm (0.51) and below 45.0 cm (0.48) indicating generalised feeding. This primary study from Bay of Bengal is the first comprehensive report on trophodynamics for the species and would contribute to its management using trophic interactions.
The European oyster Ostrea edulis played a key role in the North Sea by providing several ecosystem functions and services. Today, O. edulis is classified as severely degraded or functionally extinct in Europe. Marine conservation is focusing on biogenic reef restoration, namely the restoration of O. edulis in Natura 2000 sites of the North Sea. The identification of oyster larvae related to natural spatfalls of restored reefs and monitoring of larval drift is a key aspect of marine protected area management. Morphological identification and distinction from other abundant bivalve larvae using microscopy is difficult. Existing molecular biological methods are expensive and bound to stationary laboratory equipment, or are inadequate in the visualization. In this study, we identified nucleic acid lateral flow immunoassay (NALFIA), a well-established tool in human pathogen diagnostics, as an efficient approach for point-of-care (POC) testing in marine monitoring. Based on the genetic sequence of the mitochondrial cytochrome b of O. edulis , forward and reverse primers were developed. The reverse primer was labelled with fluorescent dye FITC, forward primer with biotin. Reaction on the lateral flow stripe could be realized with a single O. edulis larva in direct PCR with multiplex primers in a portable PCR-cycler. The established NALFIA system can distinguish O. edulis larvae from Crassostrea gigas and Mytilus edulis larvae, respectively. This method offers new approaches in POC testing in marine research and monitoring. It gives quick and clear results, is inexpensive, and could be easily adapted to other species of interest.
A factorial trial was conducted to detect the effect of different feeding strategies of supplementation of effective microorganisms (EM) liquid on the growth performance, feed utilization, body chemical composition and economic efficiency of monosex Nile tilapia ( Oreochromis niloticus ) juveniles. Three experimental treatments were formulated a basal diet without any addition of EM (control; A), a diet supplemented with 2% EM (B), and a diet supplemented with 4% EM (C). All treatments were offered to fish through two different strategies of feeding the meal: 2/3 in the morning and 1/3 in the afternoon or 1/3 in the morning and 2/3 in the afternoon. Each treatment was replicated three times. Juveniles Nile tilapia with an average initial body weight of 3.85 ± 0.22 g (± SE) were randomly stocked at a rate of 90 juveniles per 1.5 m ³ tank. Fish growth performance and feed utilization significantly ( P ≤ 0.05) increased with increasing EM supplementation and were positively affected by different feeding strategies. Moreover, the economic evaluation showed that there were more benefits by when using the 4% EM diet and feeding 2/3 of daily meal in the morning.
The acoustic camera is a non-intrusive method increasingly used to monitor fish populations. Acoustic camera data are video-like, providing information on fish behaviour and morphology helpful to discriminate fish species. However, acoustic cameras used in long-term monitoring studies generate a large amount of data, making one of the technical limitations the time spent analysing data, especially for multi-species fish communities. The specific analysis software provided for DIDSON acoustic cameras is problematic to use for large datasets. Sonar5-Pro, a popular software in freshwater studies offers several advantages due to its automatic tracking tool that follows targets moving into the detection beam and distinguishes fish from other targets. This study aims to assess the effectiveness of Sonar5-Pro for detecting and describing fish passages in a high fish diversity river in low flow conditions. The tool's accuracy was assessed by comparing Sonar5-Pro outputs with a complete manual analysis using morphological and behavioural descriptors. Ninety-eight percent of the fish moving into the detection beam were successfully detected by the software. The fish swimming direction estimation was 90% efficient. Sonar5-Pro and its automatic tracking tool have great potential as a database pre-filtering process and decrease the overall time spent on data analysis but some limits were also identified. Multi-counting issues almost doubled the true fish abundance, requiring manual operator validation. Furthermore, fish length of each tracked fish needed to be manually measured with another software (SMC). In conclusion, a combination of Sonar5-Pro and SMC software can provide reliable results with a significant reduction of manpower needed for the analysis of a long-term monitoring DIDSON dataset.
Supplementation of biofloc in rearing of common carp ( Cyprinus carpio ver. Communis (0.84 ± 0.003 g) was tested in replacing costly feed and environmental amelioration. Neem ( Azadirachta indica ) leave extract in biofloc media has beenknown to be beneficial in controlling pathogenic Vibrio sp. in brackish water shrimp. Two studies were conducted for 120 days in outdoor experimental cisterns with reduction of feed from 50% to 100%, with two biofloc media; without (Experiment 1; E1) and with neem extract (Experiment 2; E2). The experimental groups were: biofloc with feeding at 6% body weight (T1E1 and T1E2), biofloc with feeding at 3% body weight (T2E1 and T2E2), biofloc without feeding (T3E1 and T3E2), feeding at 6% body weight (C1) and only biofloc (C2E1 and C2E2). Absolute weight gain in T2E1 (9.96 g) was 8.23% and in T2E2 (9.56 g) was 4.39% higher than C1 (9.14). In spite of 5.04% and 13.98% higher growth respectively in T1E1 (10.50 g) and T1E2 (11.66 g) than C1 (9.97 g), BFT could not compensate the total withdrawal of feed (T3E1 and T3E2) and resulted in 22.22% to 33.33% mortality in T3E2 and T3E1 respectively. Under identical feeding regime, FCR was improved by 52.57% to 53.76% in T2E1 (1.84) and 48.71% to 51.23% in T2E2 (1.99) compared to T1E1 (3.98) and T1E2 (4.08). Absolute weight gain in T2E1 was 8.97 times and in T2E2 was 4.63 times higher than C1. In spite of 18.54% and 7.26% higher growth respectively in T1E1 and T1E2 than C1, BFT could not compensate the total withdrawal of feed (T3E1 and T3E2) and resulted in 22.22% to 33.33% mortality in T3E2 and T3E1 respectively. Under identical feeding regime, FCR was improved by 52.57% to 53.76% in T2E1 and 48.71% to 51.23% in T2E2 compared to T1E1 and T1E2 respectively. Increased N: P ratio of water and soil in E2 favoured fish growth. Neem leave extract in biofloc media should be judicious as it may cause nitrification inhibition.
The movement of fish eggs and larvae in bay and estuarine systems is affected by freshwater discharge. In this study, the assemblage structures of ichthyoplankton eggs and larvae were assessed for the first time in Jinju Bay, South Korea, to identify the spawning and nursery functions of the bay. Fish eggs and larvae and several environmental parameters were sampled monthly from April 2015 to March 2016 inside and outside of the bay. Within the bay we collected eggs and larvae from 25 and 35 species, respectively, indicating greater diversity than outside the bay, where we collected eggs and larvae of 20 and 28 species, respectively. Fluctuations in water temperature and salinity were larger inside than outside of the bay, and chlorophyll-a concentration was higher within the bay, likely due to discharge from the Namgang Dam, which causes water to flow from the inside to the outside of the bay. This process influences fish larva abundance, such that more larvae are found outside than inside the bay. We also found that 28 fish species use Jinju Bay as a spawning ground. For some species, the timing of egg and larva appearance differed inside and outside of the bay, suggesting that the timing of spawning may differ between the two environments.
Theory suggests the use of individual transferable quotas (ITQs) as a solution to overcapacity and to keep efficient fishers active. While the reduction of overcapacity under ITQ implementation is well documented, empirical evidence on the role of capacity utilisation in adjusting the labour force is scarce. This article analyses whether the capacity utilisation of the vessels that fishers own/work on influences their probability of continuing fishing or whether factors such as fishing income and pension are more important. Danish small-scale fisheries with vessels less than 17 m in length, in which ITQs were introduced in 2007, are studied using a multinomial logit regression based on a unique dataset of individual income and socioeconomic characteristics of Danish fishers in the period 2002-2012 as well as individual vessel data. Together with other relevant socioeconomic variables, vessel capacity utilisation is included in the regression. The latter is identified in a productivity analysis of all commercial active vessels using Data Envelopment Analysis. It is found that increasing vessel capacity utilisation both significantly and positively influences the decision to stay in a small-scale fishery. Increasing income from fisheries also significantly influences the probability of staying in the fishery business. The Danish results provide evidence that the most efficient fishers are those who remain active when ITQs are implemented.
The potential of biofloc media in in-situ environmental amelioration mediated through the removal of nitrogenous metabolites, reduce the dominance of disease-causing Vibrio to beneficial Bacillus community and reduction of costly commercial feed was investigated in white leg shellfish ( Litopenaeus vannamei ) farming. Three treatments viz. biofloc without neem + commercial feed (B), biofloc with neem +commercial feed (NB), only commercial feed without biofloc (F)and, one control (C) withno biofloc and no feed in triplicate was applied with a stocking density of 60 PL-20 m ⁻³ in outdoor earthen ponds (1000 m ³ ). Two biofloc media (C:N = 15–10:1) with and without neem leave extract were applied with reduction of feed supplement from 50% to 100%. The significant difference was observed in final body weight (33.82 ± 0.18 g) in neem based biofloc media than the other tested shrimp with the survival percentage above 87%. Superiority of biofloc based rearing system over the traditional feed based one was established as live weight gain was 28.48–137% more with a reduction of feed conversion ratio by 7.60% to 8.18% in the former. Moreover, feed cost was reduced both in B (8.1%) and NB (8.77%) compared to conventional feed −based culture system (F). The nutrient profile of floc and shrimp also improved as higher protein content was recorded in floc (18.65–19.63%) and shrimp (24.58–26.29%). The development of biofloc within the culture system resulted in cumulative increase of Bacillus population with concomitant decrease of luminous Vibrio population. The findings of the study strongly indicated that biofloc technology could be a potential tool of ecosystem approach towards in-situ environmental amelioration in shrimp farming ponds with substantial reduction of cost towards feed, aqua chemicals used for disease and environmental health management and other operational cost like water exchange.
Unreliable information on harvest potential is a persistent challenge for the Indonesian government and industry alike to manage an efficient supply chain of seaweed raw material. The use of remote sensing technology to assess seaweed harvest potential has been scarcely available in the literature. This current research aimed at estimating the harvest potential of seaweed Kappaphycus alvarezii through remote sensing using supervised classification with maximum likelihood (MLC) and contextual editing (CE) methods. This research evaluated the capabilities of different band combinations along with depth invariant index (DII) to enhance the remote sensing accuracy in estimating seaweed harvest potential. The seaweed classification using Worldview-2 imagery was compared with the in-situ references (ground-truthing). The potential data bias resulted from different imagery acquisition timestamps with the in-situ measurement was kept minimal as both data time stamps were ten days apart and within the same seaweed culture cycle. The average dry weight of all seaweed samples collected during the research was 924 ± 278.91 g/m ² with culture ages between 1 and 40 days. The classification results based on MLC+CE with a 5-band combination method without DII showed a better correlation and closer fit with the in-situ references compared to the other methods, with an overall accuracy of 79.05% and Tau coefficient value of 0.75. The estimated total harvest potential based on the combined seaweed classes was 531.26 ± 250.29 tons dry weight.
The shifting policy focus towards Ecosystem Based Management in Fisheries (EBFM) requires the integration of knowledge and disciplines and the engagement of stakeholders to support decision-making processes. Scientists contribute to this through (i) participatory research projects, (ii) stakeholder partnerships and (iii) institutional scientific advice processes. Understanding the role of scientists in such processes, the nature of the interactions between scientists, stakeholders and managers in knowledge integration and the link between science and policy is an emerging field of research addressing transdisciplinary challenges. In 2018, Ifremer-UMR AMURE organized the workshop 'Science, Partnership and Decision-support in Fisheries' bringing together international scientists from natural and social sciences to conduct a review based on twenty concrete case studies. Findings indicate that science-stakeholder-manager partnerships for decision-support in fisheries can play an essential role in the transition to EBFM. To foster this transition, eight recommendations are presented that cover the roles of the different participants, the expectations of partnerships, capacity building, the integration of the social sciences, and funding structures. Further, it is recommended that future research and innovation framework programmes into sustainable fisheries and other ocean uses should explicitly include mechanisms to foster transdisciplinary approaches and the development of best practices. Building-up networks and developing reflexive approaches to review experiences and practices for transdisciplinary approaches in EFBM decision-support will contribute to design the next generation transdisciplinary platforms and generating actionable knowledge towards EBFM. Keywords: Ecosystem-based approach to fisheries management / participatory approach / stakeholder engagement / transdisciplinary approaches / role of science / collaborative research
In-situ identification of fish species using acoustic methods is a key issue for fisheries research and ecological applications. We propose a novel approach to fish discrimination based on the relationship between target strength frequency response (TS(f)) and vertical swim velocity (VSV), as a proxy of fish body orientation. The measurements were carried out with a wideband echosounder on live fish of five species confined in a net cage. The data show a large dependence of TS(f) on VSV. To compare the variability of frequency responses of different fishes, we calculated ΔTS(f, VSV) as the difference between the TS(f) at given VSV and the TS(f) at VSV = 0, i.e. when the fish was swimming horizontally. We demonstrated that the relationships between ΔTS and VSV were similar for fish of the same species but dissimilar for different species. This implies that the acoustic fish discrimination in nature might be performed when the variations of the VSV can be measured from acoustically tracked fish. This can be a promising method for remote fish discrimination, for instance, for fish with diurnal vertical migrations. Further validation of this approach for fish recognition is required.
The maturation of anadromous whitefish ( Coregonus lavaretus ) was analysed from samples taken from commercial coastal fishing in 1998–2014 in the Gulf of Bothnia. Whitefish matured at a younger age from year to year. The proportion of older (5–12 sea years) mature males decreased from 79% to 39% in the northern Gulf of Bothnia (66°N–64°N) and from 76% to 14% in southern (64°N–60°30'N) during the study period. At the same time, the proportion of young males (2–4 sea years) increased. Whitefish matured younger: the proportion of mature fish at age four increased in both the north and south among females (13% → 98%; 6% → 85%) and males (68% → 99%; 29% → 89%). The catch length of four-year-old fish increased during the study period in both sexes. In contrast, the length of six-year-old females decreased from year to year. Sea surface temperatures increased during the study period, and were possibly associated with a decrease in the age of maturation and faster growth.
Parapenaeopsis stylifera , a major commercial penaeid shrimp fishery resource in the Indian Ocean, has lacked adequate information on life history parameters for nearly two decades. In this study, growth and mortality parameters of P. stylifera from the southwest coast of India were estimated using length data and used to derive biological reference points for the species. The asymptotic length for females was L ∞ = 131 mm; k = 1.1 y ⁻¹ and for males L ∞ = 117 mm; k = 1.25 y ⁻¹ . Mortality parameter estimates were Z = 4.42, M = 1.24, F = 3.18 y ⁻¹ and exploitation rate E = 0.72 for females; Z = 5.76, M = 1.39, F = 4.37 y ⁻¹ and E = 0.76 for males. Thomson and Bell yield biomass, Beverton and Holt yield per recruit, and relative yield per recruit models were applied to predict the stock status and length cohort analysis for estimating the stock size. The Beverton and Holt analysis gave E max = 0.69 in females and 0.75 for males, which is below the E current values obtained for the sexes. The Thomson and Bell analysis indicated that if F current at which the yield is 121 460 t in females and in males 128 064 t is further increased, rise in yield will be modest. B/B 0 and SB/SB 0 at F current were 24% and 18% for females and 21% and 16% for males, respectively. Target reference point F 0.1 and F 0.5 at different levels of age at capture t c (0.5, 0.6, 0.7 and 0.8 yrs) was estimated by Beverton and Holt yield per recruit model. The outcome from these models forms integral inputs for multispecies/multigear tropical fisheries management. Parapenaeopsis stylifera is one of the inshore penaeid shrimp identified by the Marine Stewardship Council for certification from the region and, moreover, biological reference points are a prerequisite to assessment and management of tropical multispecies fisheries for ecosystem-based fisheries management.
The mutable nassa, Tritia mutabilis, a marine gastropod that is widely exploited on the Adriatic coast is an important source of income for small-scale fishermen in the Mediterranean Sea, particularly in the Gulf of Lion. However, the lack of knowledge on the ecology and biology of this species limits our capacities to propose and produce an effective management plan. As a result, stocks are currently declining, especially in Italy. In order to optimize a management plan for this fishery, we designed a study to better characterize the reproductive biology of T. mutabilis, using gonad histology and performing a regular monitoring of population size frequency. The average shell height of individuals during the breeding period was 24 ± 2.7 mm for males and 30 ± 3.7 mm for females. The presence of small females (10 mm) and large males (32 mm) in the whole sample challenged previous assumptions regarding protandry (sex change from male to female). The size at first maturity was estimated for males and females at 17.5 mm and 24.4 mm shell height, respectively. In Italy, current management measures include a minimum conservation reference size of 20 mm in shell height. Therefore, it is likely that many individuals that did not reproduce are being caught, which could partly explain the decline observed, despite conservation measures introduced more than ten years ago. Overall, our study provides some baseline information to establish, in consultation with fishermen, management measures for this small-scale fishery in France.
Siniperca chuatsi and Siniperca kneri are two economically important freshwater fishes endemic to East Asia. Recently, some Siniperca specimens collected from Lake Poyang and Lake Dongting in the middle reaches of the Yangtze River couldn't be clearly identified as they showed intermediate morphological characteristics between S. chuatsi and S. kneri, and some inter-species hybrids were detected by microsatellite loci. To further verify genetic composition of these intermediate individuals, and determine the prevalence and degree of introgression between the two Siniperca species, a large set of high-quality, independent, diagnostic genetic markers were necessarily required. Based on enrichment and sequencing of target genes in sinipercid fishes, 463 loci (F ST = 1) between S. chuatsi and S. kneri were selected and verified for species diagnosis. A total of 349 loci with 458 diagnostic SNPs were identified for discriminating S. chuatsi and S. kneri . From those markers, 224 diagnostic SNPs (only one SNP per locus) were selected to identify and categorize 48 specimens with intermediate morphological characters. The results showed that there were 8 specimens identified as hybrids, 8 specimens as S. chuatsi and 32 specimens as S. kneri. NEWHYBRIDS analysis showed that the hybrid offsprings were composed of the first-generation hybrid (2 individuals), first-generation backcross (1 individual), second-generation backcross (1 individual) and fourth-generation backcross (4 individuals), and the backcrossing could happen to both S. chuatsi and S. kneri . These hybrids could occur naturally, or escaped from farmed fish, due to extensive artificial breeding practice in these regions. However, the origin of the introgressive hybridization can't be easily traced. Therefore, some measures for protecting genetic resource of Siniperca speies in the Yangtze River should be enforced, such as assessing genetic background of the cultured stocks, reducing the escapement from farmed fish, and monitoring the trend of introgressive hybridization between Siniperca species in the future.
The genus Parapenaeopsis is an important group of marine shrimps for wild capture in the Indo-West Pacific region. Phylogenetics of penaeid shrimps is still a debatable issue. This study focuses on the phylogenetic relationships among seven species within the genus Parapenaeupsis, the population genetic variation of Parapenaeupsis sculptilis along Bangladesh coastline of the Bay of Bengal and the phylogeography of P. sculptilis in the Indian Ocean region by analysing cytochrome oxidase subunit 1 barcode (CO1) sequence. No population structure was detected in P. sculptilis collected from two sampling sites along the Bangladesh coastline (AMOVA and Φ ST = ‑0.014, p > 0.05; F ST = 0.061, p = 0.04), which expanded first around 73 (CI: 36‑119) kyr ago. The genealogical relationships in Bangladesh P. sculptilis population are shallow with haplotype diversity (h) of 0.58 and nucleotide diversity (π) of 0.0014. The different P. sculptilis samples from Bangladesh, India and Mozambique of the Indian Ocean revealed connectivity between western Indian Ocean and the Bay of Bengal. The phylogeny within the genus Parapenaeupsis showed a polyphyletic relationships for P. hardickwii and its taxonomy needs to be reevaluated. The study will help for genetic upgradation in aquaculture and monitoring of the population genetic diversity of P. sculptilis.
Recreational fisheries are an important element of contemporary fisheries. Detailed information about the motivation and opinions of anglers regarding catch-and-release fishing in post-communist countries, such as Poland, has not been widely available to date. The aim of this study was to fill this gap. We obtained 936 survey questionnaires completed by anglers from throughout Poland. The mean annual catch of a Polish angler is 126 fish weighing 46.1 kg. Anglers catch mainly cyprinids, but they would prefer to catch large predatory fishes, and they spend an average of 416.50 EUR on this activity annually. These results confirm the hypothesis that angling catches in Poland are decidedly of a recreational character and that catches targeted at fish consumption are of lesser importance. Simultaneously, we determined that younger anglers are more willing to release caught fish than older anglers.
Many fishing fleets operate in mixed fisheries where several target species are caught together along with other bycatch species unintentionally caught. In some cases, fleets operate in multiple mixed fisheries depending on various factors such as time of year or current market conditions, among other factors. Data collection in the European Union (EU) involves various levels of detailed data. Economic data is generally collected on an annual time-step whereas other sources provide information at much higher resolution such as the fishing trip (landings declarations), fish day (logbook) or even in real-time (electronic logbook). In this paper a methodology is described to disaggregate the annual cost of a fleet segment into a cost per fishery and per species within the fishery. This information is of interest as it permits incorporation of the economic implications of fishery dynamics into fisheries management. Assessment of these unit costs on a fishery basis also allows accurate input into value chain analysis which is carried out on a species basis.
Species specific identification of early larval stages of many decapod crustaceans sampled from plankton collections remains cumbersome owing to lack of distinguishable characteristics, where DNA based molecular methods provide accurate results without taxonomic ambiguities. In the present study, an attempt was made to detect temporal occurrence of early zoea of freshwater prawn Macrobrachium rosenbergii (de Man) using real-time PCR assays in polyhaline, mesohaline and oligohaline areas of a tropical positive estuary, the Vembanad lake (S. India). High caridean larval abundance could be recorded in polyhaline areas in all seasons while it could be recorded in monsoon season in mesohaline and oligohaline areas. 113 DNA isolations were successfully made from morphologically identified taxonomic units (MOTU) and SYBR Green based RT-PCR amplifications using designed primer for M. rosenbergii yielded positive detections in 38 samples (34%) representing all seasons in all three zones. Positive detections could be recorded in all months except May in mesohaline areas and differed significantly (F = 17.2 p < 0.01) with the same in polyhaline and oligohaline areas. The present results of molecular detection of M. rosenbergii larvae extend confirmation of its breeding ground in Vembanad lake where appropriate management strategies could be enforced for stock conservation of this species.
The high losses in shrimp production due to mortality caused by Vibrio opportunistic pathogens still constitute a significant challenge in the shrimp industry. Synbiotic feed supplementation appears to be a promising control strategy to maintain healthy shrimp stock. In this study, the effects of synbiotic-containing prebiotic seaweeds Kappaphycus alvarezii and Spirulina sp. as well as probiotic Halomonas alkaliphila were evaluated on the survival, growth, and vibriosis of Litopenaeus vannamei during the post-larval stage. Five different feeds were tested: commercial feed, prebiotics K. alvarezii and Spirulina sp.-supplemented feed, and synbiotic-supplemented feed using K. alvarezii, Spirulina sp. and probiotic H. alkaliphila with different concentrations of 10 ⁸ , 10 ⁹ , and 10 ¹⁰ CFU.kg ⁻¹ . Following 14 days after the feeding test, the highest shrimp survival (91.46 ± 0.05%) was obtained in the treatment group fed with synbiotic-supplemented feed containing 0.375% K. alvarezii , 0.125% Spirulina sp., and H. alkaliphila at 10 ⁹ CFU.kg ⁻¹ ( p < 0.05). A 7-day challenge test against opportunistic bacteria Vibrio harveyii was then performed using three treatment groups: (1) synbiotic, containing 0.375% K. alvarezii , 0.125% Spirulina sp., and H. alkaliphila at 10 ⁹ CFU.kg ⁻¹ ; (2) prebiotic, with 0.375% K. alvarezii , 0.125% Spirulina sp.; and (3) control, using commercial feed. The highest shrimp survival of (79.9 ± 0.05%) was found in the synbiotic treatment group, followed by the prebiotic and control treatment groups ( p < 0.05). Overall results suggested that synbiotic-supplemented feed containing 0.375% K. alvarezii , 0.125% Spirulina sp., and H. alkaliphila at 10 ⁹ CFU.kg ⁻¹ significantly improved shrimp survival even when challenged with V. harveyii . Thus, this synbiotic can be potentially applied as an alternative biocontrol strategy against vibriosis in intensive shrimp post-larval culture.
Parentage assignment with genomic markers provides an opportunity to monitor salmon restocking programs. Most of the time, it is used to study the fate of hatchery-born fish in those programs, as well as the genetic impacts of restocking. In such analyses, only fish that are assigned to their parents are considered. In the Garonne-Dordogne river basin in France, native salmon have disappeared, and supportive breeding is being used to try to reinstate a self-sustained population. It is therefore of primary importance to assess the numbers of wild-born returning salmon, which could appear as wrongly assigned or not assigned, depending on the power of the marker set and on the size of the mating plan. We used the genotypes at nine microsatellites of the 5800 hatchery broodstock which were used from 2008 to 2014, and of 884 upstream migrating fish collected from 2008 to 2016, to assess our ability to identify wild-born salmon. We simulated genotypes of hatchery fish and wild-born fish and assessed how they were identified by the parentage assignment software Accurassign. We showed that 98.7% of the fish assigned within the recorded mating plan could be considered hatchery fish, while 93.3% of the fish in other assignment categories (assigned out of the mating plan, assigned to several parent pairs, not assigned) could be considered wild-born. Using a Bayesian approach, we showed that 31.3% of the 457 upstream migrating fish sampled from 2014 to 2016 were wild-born. This approach is thus efficient to identify wild-born fish in a restoration program. It remains dependent on the quality of the recording of the mating plan, which we showed was rather good (<5% mistakes) in this program. To limit this potential dependence, an increase in the number of markers genotyped (17 instead of 9) is now being implemented.
The high organic waste content of river water in Demak, north coast of Java, has caused traditional small-scale pond farmers to stop stocking shrimp. This paper examines whether seaweed and mussel will improve the quality of water these farmers use. The effect of Gracilaria verucosa and Perna viridis on the water quality was assessed by measuring the removal rates (RRs) of total organic material (TOM), total ammonia nitrogen (TAN), nitrite, and nitrate. The specific growth rates (SGRs) of seaweed and mussel were also measured. Thirty-six semi-outdoor tanks containing 800 L of brackish water and 7 cm substrate were randomly assigned to four replications of four densities of G. verucosa : 50 (S50), 100 (S100), 150 (S150), and 200 (S200) g m ⁻² , and of P. viridis : 60 (M60), 90 (M90), 120 (M120), and 150 (M150) g m ⁻² . Weekly, the TOM, TAN, nitrite, and nitrate contents were measured, seaweed and mussel weighted; RRs and SGRs were calculated at the end of the study. The effect of densities on the RRs was significant for both seaweed and mussel. P. viridis was more effective in reducing TOM (by 38%) than G. verucosa (7%); G. verucosa achieved higher RRs for TAN, nitrite, and nitrate. At S200, TOM and TAN decreased by 7.4% and 67%, respectively. At M90, TOM and TAN, decreased by 38% and 49%, respectively. However, nitrite increased significantly at S200 and M150. The SGR of seaweed was significantly lower at S200 than that at S150, S100, and S50. The best performing densities were S100 and M90.
Integrated multi-trophic aquaculture (IMTA) is a way to help preserve the environment while maintaining a good level of total production. An ecologically semi-intensive pond system was designed in which a polyculture fishpond was associated with a lagoon planted with macrophytes to bioremediate the water. The properties of this “semi-intensive coupled” system (SIC) were compared to those of semi-intensive (SI) and extensive (E) systems, each of which was contained in a single fishpond with the same fish polyculture (common carp (Cyprinus carpio), roach (Rutilus rutilus), and perch (Perca fluviatilis)) as SIC. E differed in that it had half the initial density of fish, and the fish were not fed. Fish growth performances, water quality (chemical and biological indicators), chlorophyll concentrations, and invertebrate production were measured. The systems were compared based on fish production performances and physicochemical and biological characteristics, and were then described using principal component analysis (PCA). Carp and roach in the two fed systems had higher growth performances than those in E. Compared to SI, the planted lagoon in SIC, induced a decrease of 15% in fish growth performances and of 83% in total chlorophyll concentration (a proxy for phytoplankton) but improved water quality (−34%, −60% and −80%, for the concentrations of total nitrogen, total phosphorus, and blue green algae (for micro-algae in class Cyanophyceae), respectively). According to the PCA, SIC clearly differed from SI in benthic macro-invertebrate production and concentrations of total nitrogen, total phosphorus, and brown algae (for micro-algae in class Dinophyceae or a branch of Bacillariophyta) in the water. SIC differed from E in oxygen parameters (dissolved and saturation), estimated annual zooplankton production, and pH. In conclusion, the properties of a lagoon reveal perspectives for environmentally friendly practices, while using biodiversity and secondary production in order to enhance fish production.
In this study, the genetic relationships of 804 tarek ( Alburnus tarichi ) samples from a total of 18 populations, including the potamodromus and resident individuals from Lake Van basin in eastern Turkey, were studied by using nine microsatellite loci. A total of 93 alleles was detected, and the average number of alleles per locus was 10.3 ± 3.39. The mean estimated observed and expected heterozygosity were 0.340 ± 0.016 and 0.362 ± 0.015, respectively, which indicated a low level of polymorphism. After Bonferroni correction ( P < 0.0027), the multi-locus test applied to each population revealed that 12 out of 18 populations were in Hardy-Weinberg equilibrium (HWE) ( P = 0.0120–0.9981). Analysis of molecular variance (AMOVA) showed more than 76% genetic variability within individuals and 19% among populations, which was significantly higher than zero (F ST = 0.19), and furthermore, a low level of genetic variation was observed among individuals within populations (4.84%: F IS = 0.06). Bayesian clustering analysis indicated that the total genetic variation grouped into 3 clusters. Additionally, the significance test results revealed that 11 of the 18 populations are threatened with extinction due to recent bottleneck events.We conclude that the tarek populations from the Lake Van basin can be classified into distinct genetic groups, based on microsatellite information. In addition, our results provide essential information for the development of a management plan that conserves the tarek's genetic diversity and achieves a sustainable fishery.
Trade with marine species as ornamentals is an important sector of the international pet trade. The vast majority of these species are collected from the wild and one of the top supplying countries is Indonesia. Detailed evidence on trade with marine resources in Indonesia is lacking or it is hardly accessible. Moreover, the exploitation of ornamental species seems to be mostly uncontrolled. This study presents detailed characteristics of such trade for Indonesia, including the offered species, their sizes, prices, and conservation status, based on data and information obtained from wholesalers in 2018. The main provinces of marine wildlife collecting are also identified. In total, 777 marine vertebrate and invertebrate species were traded, belonging to 174 families including two species classified as endangered: Banggai cardinal fish ( Pterapogon kauderni ) and zebra shark ( Stegostoma fasciatum ). Commonly traded was red lionfish ( Pterois volitans ), known to be a successful invader. The volume of ornamental marine fish exported from Indonesia in period 2015–2019 was 3 353 983 kgs sold for 33 123 218 USD. The province of Bali was identified as the main exporter of ornamental marine fish within Indonesia. These findings should help to establish sustainable exploitation of marine resources in relation to conservation and wildlife management.
The Strait of Messina is located at the centre of the Mediterranean Sea and is considered a biodiversity hotspot and an obligatory seasonal passage for different pelagic species such as sharks, marine mammals, and billfishes. For the first time, in the Strait of Messina, our research group tagged a Mediterranean spearfish (Tetrapturus belone) using a pop-up satellite archival tag (PSAT). The observation of abiotic parameters (depth, light, and temperature) recorded by the PSAT confirmed that the tagged specimen was predated after about nine hours. The tag was then regurgitated 14 days after the tag deployment date. The analysis of collected data seems to indicate that the predator may be an ectothermic shark, most likely the bluntnose sixgill shark (Hexanchus griseus).
In the Archipelago Sea, pikeperch ( Sander lucioperca ) is an important species in both commercial and recreational fisheries. Pikeperch is caught mainly with small mesh size gillnets, and annual fishing mortality is high. The possible effects of such fisheries, as well as temperature or density on pikeperch growth have not been studied earlier. The first hypothesis of this study was that the effect of temperature on growth is positive and that of density is negative. The second hypothesis was that size-selectivity of gillnets causes the fast-growing individuals to be caught at younger ages than the slow-growing ones. The results showed that temperature had a significant positive effect on growth, and this was greater than the negative effect of year-class density, which was also significant. The gillnet selectivity caused a difference of up to 60 mm in back-calculated lengths in the fully recruited age groups within the same year class, between pikeperch caught at age 6+ and age 9+. Thus, the Rosa Lee phenomenon caused by gillnet size-selectivity led to the removal of faster growing specimens from the population at younger ages. This can potentially cause underestimation of real growth, and thus, poor fishery management.
Mariculture cage farming in Oman is in its infancy stage. This study provides important baseline information about the initial state of mariculture in Oman and for the sustainable management of future local cage farming. Our main objective was to evaluate the spatio-temporal variations of water quality and hydrography around a gilthead seabream ( Sparus aurata ) cage farm in Quriyat (Sea of Oman). Starting in July 2018, we conducted a monitoring program over one year in which physico-chemical variables and nutrient levels were regularly measured at the farm cages and at reference sites away from the farm. Vertical flow profiles were recorded at the farm and analysed together with remotely sensed data. The results showed no significant differences among physico-chemical variables and nutrient levels between cages and reference sites. However, there were clear seasonal as well as significant short-term variations in the measurements. Winter conditions are usually homogeneous over the water column without reaching extremes. In summer we recorded surface temperatures of up to 32 °C and extended periods of hypoxia below 35 m depth. Periods of pronounced stratification were interrupted by energetic irregular flow pulses that triggered short up or down-welling events which lead to strong variations of temperature and oxygen. We did not measure a significant impact of the cage farm on the local environment. Our results rather point to the particular importance of monitoring temperature and oxygen levels. Both variables can approach threshold levels for fish farming, especially during summer. We determined the relevant characteristics of the local system and defined requirements for adequate monitoring. The findings of this study provide a timely baseline for future research on the interactions between local cage farms and the marine ecosystem and will assist in the planning and management of mariculture in Oman.
European sea bass and Ulva sp. were co-cultured in different tanks of an indoor Recirculating Aquaculture System ( Ulva -RAS) with bacterial biofilter, in an effort to optimize the efficiency of the system and to further decrease the waste effluent. A system with similar culture conditions, without Ulva, was used as a control-RAS to elucidate integration effects on growth performance and chemical composition of sea bass. The role of Ulva on N and P concentrations, gas (O 2 , CO 2 ) and pH in water was also investigated. Fish were fed a diet of fish oil replacement (55%) with a mixture of rapeseed oil and palm oil (1:1). Our data showed that Ulva could uptake N and P nutrients, but could also enrich sea water with phosphates. Sea bass reared in Ulva- RAS exhibited isometric growth, while fish in control-RAS showed a positive allometric growth and an increased variance of body weight and length. In addition, sea bass in Ulva -RAS demonstrated significantly higher levels of condition factor (K), feed intake, protein, lipid, P, EPA and DHA content (% wet weight of total body) and lipid productive value, compared to fish in control-RAS. Ulva, after bi-weekly culture, showed increased protein content (60%) compared to wild seaweed collected nearshore. Cultivated Ulva obtained dark green color, doubled chlorophyll concentrations, and exhibited lower levels of saturated and higher levels of certain monounsaturated and n-3 polyunsaturated fatty acids, indicating increased photosynthetic activity. Present results revealed the beneficial effects of Ulva on sea bass growth and quality, which led to an improved response to the nutritional stress imposed by the fish oil replacement with vegetable oils, thus contributing to a sustainable aquaculture. Moreover, it was concluded that Ulva could improve water quality by increasing pH and O 2 , reducing CO 2 and contribute to bioremediation of ammonia and nitrates from water in integrated aquaculture.
The objective of this study was to determine the population distribution and some biological aspects for fish stock assessment of the greater forkbeard Phycis blennoides along the Algerian basin. The distribution of P. blennoides (3418 individuals) was studied using data collected between 170-779 m depth during two bottom trawl surveys developed on 2003 and 2004. Additionally, some biological parameters were obtained from 1050 individuals sampled from commercial fisheries in Algerian ports (i.e. Annaba, Azeffoun, Dellys, Cap Djinet, Zemmouri, Bouharoun, Algiers, La Madrague, Cherchell, Tenes and Mostaganem) during the period 2013-2017. P. blennoides sampled from bottom trawl surveys showed a depth related distribution with the largest individuals being found at 600-800 m depth and the smallest at shallower depths. Density and biomass varied with depth and density also with longitude, while biomass showed no pattern with longitude. Recruitment was recorded in the eastern sector of Algeria during winter, for individuals sampled by bottom trawl surveys. Young P. blennoides entered commercial fisheries in summer, with an overall sex ratio skewed towards males (1F:2.18M). The size at first maturity (L50) was 24.30 cm and 30.39 cm for males and females, respectively. The age at 50% maturity was 2-3 years for specimens collected by a bottom trawl survey in 2003 and commercial fisheries, but 3-4 years for the bottom trawl survey in 2004.
Key-words: Phycis blennoides, density, biomass, maturity, exploitation, Algerian basin.
The study evaluated some population parameters of Sarotherodon melanotheron melanotheron within a lagoon complex in southern Benin: Lake Nokoué and Porto-Novo Lagoon. Data on the total length, total weight, and sex were recorded monthly between January and December 2015 for 1,745 specimens captured by local fishermen. The asymptotic length L ∞ was estimated at 24.68 cm. The growth rate K was 0.86. The total, natural, and fishing mortalities were estimated at 2.46, 1.71, and 0.75 y ⁻¹ , respectively. The size at first sexual maturity was 8.9 and 9.2 cm, respectively, for males andfemales. The size at first capture was estimated at 9.2 cm, which indicates that fish spawn at least once before capture. The current exploitation rate of 0.31 remains below the maximum exploitation rate E max which was 0.604 but was equal to the exploitation rate retaining 50% of the biomass of the stock ( E 0.5 = 0.324). This suggests that the stock of S. m. melanotheron is not overexploited in the complex. However, it is recommended that the actual rate of exploitation be kept as it is to ensure a sustainable management of these fish populations.
Selecting an appropriate growth pattern for individual fish is a meaningful but complex topic in fishery research. We model four growth functions − the commonly used von Bertalanffy growth model (VBGM), and the Gompertz growth model (GGM), Schnute–Richards growth model (SRGM), and generalized VBGM (G-VBGM) − to examine possible growth patterns. Mean total length-at-age fish datasets for five commercial fish species (yellow perch Perca flavescens, walleye Sander vitreus, northern pike Esox lucius, largemouth bass Micropterus salmoides and lake herring Coregonus artedi) from North American freshwater ecosystems, were analyzed. Using a Markov chain Monte Carlo (MCMC) algorithm, we structured four models combining informative priors of model parameters. It is the first time that deviance information criterion (DIC) and leave-one-out cross-validation (LOOCV) were combined to select the best growth model. During the model-selection process, the smooth LOOCV error successfully followed the trend of the LOOCV error, although there were difference in the curve shapes. Values of scale reduction factor (SRF) for all four models indicated convergence, ranging 1.02–1.06, below the 1.2 threshold. The GGM was selected for C. artedi, and the G-VBGM for the other four species. Our approach provided a robust process in model-selection uncertainty analysis, with the G-VBGM having the best prediction ability among our datasets.
Data obtained from licenses of spearfishers and surveys conducted in 2004 and 2017 allowed do the analysis, for the first time, of the practice of spearfishing in the Madeira archipelago. Only a small percentage of the population practices spearfishing, mostly local young men. Most of them practice the activity with a partner throughout most of the year and along most of the island's coastal areas, although preferentially along the North and Southeast coast. Results show how, in recent years, despite the population of spearfishers decreasing, the abundance in the annual catch potentially increased, probably due to the higher investment of time in this activity. It has been observed that many fishers complement their catches with manual collecting of invertebrates. Overall, 40 teleost fishes and also 4 crustaceans and 8 molluscs were identified. The most frequently captured fish species were parrotfish and white seabream, while limpets were the most collected invertebrates in both selected periods.
Seaweeds are considered as a functional food across many regions of the world and has an increasing consumption trend due to its health benefits. However, there is a concern regarding the amount of heavy metals and metalloids present in seaweeds. Therefore, the study aimed to assess the levels of metals present in specific seaweeds and its potential impact on consumption. Considered metal ions were Arsenic (As), Copper (Cu) Chromium (Cr), Nickel (Ni), Cadmium (Cd), Lead (Pb) and Mercury (Hg). At the assessment done at four different sites in the coastal regions of Sri Lanka for chlorophytes, rhodophytes and phaeophytes. Concentration of metals were analyzed using the ICPOES. According to the arrived results, concentration of metals varies as Cr > Ni > Cd > Cu > As > Pb = Hg with having zero concentration for Hg and Pb for all varieties and all sites. It was also found that the least amounts of metals were present at Jaffna site in phaeophytes ( Sargassum sp.) and chlorophytes ( Ulva sp.) When considering the Hazardous Index of the varieties, least was found in Sargassum sp. in Jaffna site. Studies were repeated for 2 seasons and there are significant differences ( p < 0.05) between the dry season and wet season in the concentration of heavy metals present. However, since the seaweeds are grown for commercial purposes only in Jaffna area, it is evident that the chlorophyte and phaeophyte varieties claim very low health risk for potential heavy metals and are suitable for consumption purposes.
In Tokyo Bay, the harvestable quantity of asari (Manila) clams Ruditapes philippinarum has been decreasing since the late 1990s. We conducted a field investigation on clam density in the Banzu culture area from April 1988 to December 2014 and collected records spanning January 1986 to September 2017 from relevant fisheries cooperative associations to clarify the relationship between the temporal variation in stock abundance and the production activities of fishermen. The yearly variation in clam abundance over the study period was marked by larger decreases in the numbers of larger clams. A large quantity of juvenile clams, beyond the biological productivity of the culture area, may have been introduced as seed stock in the late 1980s despite the high level of harvestable stock. The declines in harvested quantity began in the late 1990s and may have been caused by decreases in harvestable stock despite the continuous addition of seed stock clams. The harvested quantity is likely to be significantly dependent upon the wild clam population, even within the culture area, as the harvestable quantity was not correlated with the quantity of seed stock introduced during the study period. These declines in harvested quantity may have resulted from a decreasing number of operating harvesters due to the low level of harvestable stock and consequently reduced profitability. Two findings were emphasized. A certain management style, based on predictions of the contributions of wild and introduced clams to future stock biomass, is essential for economically-feasible culturing. In areas with less harvestable stock, actions should be taken to maintain the incomes of harvesters while avoiding overexploitation, even if the total harvest quantity decreases.