Wild Stocks Research Articles

Effect of protein and lipid levels in diets for adult sea urchin Paracentrotus lividus (Lamarck, 1816)

Paracentrotus lividus gonads are considered a prized seafood delicacy due to its organoleptic features. The increasing market demand for sea urchin depleted several wild stocks, thus aquaculture can play an important role in supplying high-quality animals. Nevertheless, the success of this activity largely depends on the development of nutritionally balanced diets capable of producing excellent gonads. In this study, four extruded diets formulated with low or high protein (30 and 50% dry matter (DM), LP and HP, respectively) and lipid (6 and 11% DM, LL and HL, respectively) levels were fed to wild-caught individuals (4.5 cm diameter) for 15 weeks. Twelve homogeneous groups of 15 individuals were randomly distributed by mesh cages (45 urchins/m2) within 250 L tanks in a recirculating aquaculture system (RAS) at 18 °C and a 12 L:12 D photoperiod regime. Sea urchins fed the LP/LL diet were compared to wild specimens with similar maturation stage.All experimental diets were well accepted by sea urchins and resulted in similar final body weight (42–43 g). No significant differences were observed in specific growth rate or protein efficiency ratio among diets. The HP diets led to a decrease of dry matter and energy intake resulting in the lowest feed conversion ratio (FCR). Weight gain, whole body composition and nutrient gain remained similar among dietary treatments. The gonad somatic index (GSI) varied between sex but was similar among dietary treatments (19–23%) and was higher than values observed in wild specimens (6–7%). Females had significantly higher total concentration of carotenoids than males, irrespectively of the dietary treatments. Dietary treatments and sex did not affect gonad texture (firmness and resilience) or colour parameters (brightness, redness, yellowness, chroma or hue angle), but affected gonad composition. Total carotenoid content in gonads was not affected by diets and resulted in lower values compared to wild specimens. These had higher levels of echinenone, β-cryptoxantin and β-carotene and showed higher redness and firmness values when compared to the LP/LL diet, irrespectively of the sex. Gonad lipid content and n-3 PUFA were higher in female than in male, whilst protein content showed an opposite trend, suggesting some sex related differences in the metabolic use of nutrients.This study clearly shows that it is possible to enhance sea urchin gonad yield in relation to wild animals in a RAS at 18 °C. All diets were effective in promoting gonad growth, but the diet with the lowest protein (30% DM) and lowest lipid (6% DM) level resulted in the highest gonad yield in both sexes.

Gall disease in the alginophyte Lessonia berteroana: A pathogenic interaction linked with host adulthood in a seasonal-dependant manner

Lessonia berteroana is the most highly exploited seaweed in Chile and the Americas, based on the harvesting of wild stocks. It is frequently facing overexploitation problems, which is detrimental for coastal ecosystems in northern Chile. Concomitant to its abundance problems, L. berteroana stocks have widely been found to bear tumour-like outgrowths. These circumstances triggered us to characterize this gall disease from one population on the Atacama coast. Galls are plastic in size, colouration and morphology, and all are linked to the brown algal endophyte Laminariocolax aecidioides, identified by using three different DNA markers. Gall histology revealed the presence of both pigmented and colourless endophytic filaments. The pathogenic nature of this interaction was confirmed by electron microscopy (EM), which showed a marked hyperplasia with host cells having disrupted cell walls. EM also indicated cellular modifications of the Laminariocolax endophytic network in contrast to free-living isolates (e.g. organelle and cell wall reductions, larger area of plasmodesmata in markedly undulated contacting cell walls). A one-year epidemiological survey from the same locality, supported by a generalized linear mixed model, revealed that the gall disease is strongly correlated with the age structure of a given population, the season of the year and maturity of the hosts, although in summer months almost all the population gets infected. Resistant phenotypes are therefore rare in the population, which flags the question of how harvesting, restoration and breeding programs should be carried out for these susceptible populations.

Distribution of Pseudomonas fluorescens and Aeromonas hydrophila Bacteria in a Recirculating Aquaculture System during Farming of European Grayling (Thymallus thymallus L.) Broodstock

Pseudomonas fluorescens and Aeromonas hydrophila bacteria are opportunistic pathogens that occur naturally in the aquatic environment and in the gut flora of healthy fish. Both species can pose a serious threat for fish that are highly sensitive to water pollution. The aim of this study was to determine the extent to which the amount of administered fish feed and fish biomass affect the distribution and abundance of Ps. fluorescens and A. hydrophila bacteria in a recirculating aquaculture system (RAS) during farming of European grayling (Thymallus thymallus L.) broodstock. A total of 68 water samples from the inflow, two rearing tanks and the outflow as well as 17 feed samples were collected and analyzed separately. Bacterial populations were analyzed by the culture-dependent method and a molecular method (fluorescence in situ hybridization, FISH) to detect culturable strains and viable but non-culturable strains, respectively. Fish biomass, feed and 16 water quality parameters (temperature, pH, concentration of dissolved oxygen, oxygen saturation, five-day biochemical oxygen demand (BOD5), total phosphorus, total organic phosphorus and nitrogen, orthophosphates, total nitrogen, nitrite and nitrate nitrogen, ammonia nitrogen, ammonium nitrogen, total suspended solids, and total organic carbon) were the explanatory factors. Statistically significant differences (RM-ANOVA, p ≤ 0.05) were stated in bacterial abundance in samples from the inflow, rearing tanks and the outflow. Water samples from the RAS were abundantly colonized by non-culturable Ps. fluorescens and A. hydrophila bacteria. Feed was not a source of bacteria, but a redundancy analysis (RDA) revealed that the amount of feed, fish biomass, BOD5, and total suspended solids and total organic carbon were positively correlated in both Ps. fluorescens and A. hydrophila. These parameters also influenced the distribution of both potentially pathogenic bacterial populations and contributed to the bacterial contamination of water in the RAS. Our results are particularly valuable for aquacultures that help to replenish wild stocks and rebuild populations of threatened species in natural aquatic environments.

A diet-change modulates the previously established bacterial gut community in juvenile brown trout (Salmo trutta)

The aim of the present study was to investigate the impact of dietary plant proteins on the gut microbiome of first feeding brown trout (Salmo trutta) reproduced from wild stocks and to evaluate whether the initial microbiome of brown trout fry can be permanently manipulated by the first feeding diet. Therefore, brown trout fry was fed diets based on either 0%, 50% or 90% plant-derived proteins from first feeding onwards and via 16S rRNA gene sequencing a strong dietary influence on the bacterial gut community on phylum and order level was detected. Proteobacteria and Fusobacteria were significantly enhanced when fishmeal was integrated into the experimental diet, whereas plant-derived proteins significantly promoted Firmicutes and Bacteroidetes. In order to evaluate whether the first feeding diet had a permanent effect on the initially established microbial gut community of juvenile brown trout, a cross-over diet-change was applied 61 days post first feeding. 48 days after the diet-change, the gut microbiome of all dietary groups was significantly different from the one initially established after first feeding. Moreover, the first feeding diet had no statistically significant influence on the gut microbiome after the diet-change, demonstrating no permanent effect on the gut microbiome formation.

Aquaculture and the displacement of fisheries captures.

In modern aquaculture, animal-production technology is used to increase aquatic food sources. Such controlled rearing of seafood can, in principle, shift the pressure off wild stocks and aquatic ecosystems by reducing fishing activities, which may advance marine conservation goals. We examined resource displacement-the reduced consumption of a resource due to its replacement with a more environmentally benign substitute-in fisheries. We employed panel regression techniques in an analysis of time-series data from 1970 through 2014 to assess the extent to which aquaculture production displaced fisheries captures for all nations for which data were available. We estimated 9 models to assess whether aquaculture production suppresses captures once other factors related to demand have been controlled for. Only 1 model predicted significant suppression of fisheries captures associated with aquaculture systems within nations over time. These results suggest that global aquaculture production does not substantially displace fisheries capture; instead, aquaculture production largely supplements fisheries capture.

Heavy metals in farmed and wild milkfish (Chanos chanos) and wild mullet (Mugil cephalus) along the coasts of Tanzania and associated health risk for humans and fish

In 2016, farmed milkfish (Chanos chanos) from Tanzania mainland (Mtwara), and Zanzibar islands (Pemba and Unguja) and wild milkfish and mullet (Mugil cephalus) from the Indian Ocean were collected for analyses of heavy metals (Pb, Cd, Hg, As, Al, Fe, Zn, Cu, Ni, Co and Cr) in muscles and livers. High concentrations of Pb were detected in muscles and livers from wild and farmed milkfish and wild mullet from all sites. The highest concentration of Pb was detected in wild milkfish liver from Mtwara (47.4 mg/kg ww). The Pb concentrations in fish muscle exceeded maximum levels (ML) set by FAO/WHO (0.3 mg/kg ww) in 100% of the analysed fish. Concentrations of Pb were higher in wild fish than in farmed fish. Cd concentrations were generally low. The comparison of the Hg concentration with EQSBiota indicated that Hg might pose potential health risk to 22% of the analysed fish. Median concentrations of Fe in livers from farmed milkfish from Jozani and Shakani, Zanzibar, were 40–80 times higher than the other sites. Assessment of human health risk and exposure to heavy metals indicated no potential risk from consuming the fish from the present study locations. However, the Pb concentrations exceeding ML in the fish suggests that Pb may affect the health of fish. Future investigations should include regular monitoring of heavy metals in farmed and wild fish in Tanzania for further development of sustainable aquaculture and the welfare of the wild fish stock in the coastal waters.

Fishery Depletion and the South China Sea

Fishery depletion is a driving force in the militarization of the South China Sea. Using Garrett Hardin’s theory “the tragedy of the commons” as an analytical lens, this paper explores the relationship between the lack of legitimate territory designations and the illegal overexploitation of wild fish stocks. It argues that China, as the regional hegemon, has triggered conflicts by pursuing an agenda of maritime territorial expansionism. Some Southeast Asian countries, affected by these resource-driven incursions, defend their exclusive economic zones through military buildup. Therefore, the rising violence and decreasing availability of fish force some non-commercial fishermen to pursue piracy as an alternate form of income. The findings of this paper suggest that increased militarism of the South China Sea has not only predominantly affected the lives of non-commercial fishermen but also negatively impacted the regional environmental health. In the future, without multilateral resource management, this militarization will only worsen.

The future of genetic engineering to provide essential dietary nutrients and improve growth performance in aquaculture: Advantages and challenges

Advancements in gene technology in recent years have been driving the aquaculture industry forward. Improvements in growth performance, feed efficiency, and omega‐3 content are goals of the industry that could capitalize on applications of genetic engineering. One of the major challenges in the industry is to reduce the use of fish meal and oil, to improve the environmental and economic sustainability of aquaculture. The recent development of genetically engineered feed ingredients is one potential solution to the looming problem of fish meal and oil dependency. Furthermore, the development of transgenic fish has potential to improve production efficiency and other future desirable characteristics that relate to feed utilization and product quality. New gene technologies are beginning to revolutionize how we produce our food, and in aquaculture, will ultimately reduce pressure on wild fish stocks, help to preserve natural aquatic ecosystems, and improve nutritional profiles of farmed fish for human consumption. The purpose of this review is to provide an update on the current applications of genetic engineering technology to improve aquaculture through nutrition, including the development and use of transgenic feed ingredients, transgenic fish, and ultimately their impacts on nutrition, product quality, and consumers.

Tracing individuals and populations of the tambaqui, Colossoma macropomum (Cuvier, 1818), from Brazilian hatcheries using microsatellite markers.

In recent years, tracing of alimentary produce of animal origin has become increasingly important, for economic, food safety and ecological reasons. The tambaqui, Colossoma macropomum, is the native fish most farmed in Brazil. The reliable identification of the origin of tambaquis (wild or farmed) offered for sale to the general public has become necessary to satisfy regulatory norms and uphold consumer confidence. Molecular methods based on the analysis of DNA sequences have often been used to evaluate the potential for tracing farmed fish, given their reliability and precision. Full likelihood and Bayesian approaches proved to be the most efficient for the identification, respectively, of individuals and populations for most of the fish sampled from seven hatcheries and one wild stock. The exclusion method and genetic distances were the least effective approaches for the identification of individuals and populations. The Bayesian method identified correctly more than 99% of the fry from most stocks, except those of the Santarém hatchery and River Amazon wild stock, which presented the best results for individual identification. The identification of populations was effective for most hatcheries, although the identification of individuals from most stocks was hampered by the reduced genetic variability. © 2018 Society of Chemical Industry.

The Status of Mussel Health Assessment and a Path Forward

Declines of freshwater mussel (order Unionida) populations worldwide are attributed to habitat degradation, pollution, and invasive species, among other factors. However, these purported causes do not fully explain the enigmatic decline and large-scale die-offs of mussels that have occurred in apparently healthy streams across a wide geographic region. The roles of the microbiota and pathogens in mussel health have been understudied, and, as a result, few data exist to compare the microbiota of healthy mussels to that of stressed or dying mussels. Captive propagation and stocking programs have expanded across the globe without standard diagnostic protocols to assess health or potential diseases in hatchery-reared or wild stocks. Nonindigenous species, contaminants of emerging concern, and anthropogenic climate change could alter adversely the underlying processes that support mussel health, such as nutritional status and microbial composition, and these factors could increase the risk for outbreaks of opportunistic and emergent mussel disease. We propose a coordinated, collaborative, and multidisciplinary effort to advance methods for assessing freshwater mussel health. We identify research and resources needed to answer central questions surrounding mussel health, including identifying potential agents of disease, defining clinical signs of declining condition, refining stress-specific biomarkers for health assessment, and developing protocols specific for mussels.

Challenges and opportunities regarding the use of alternative protein sources: Aquaculture and insects.

The world population is constantly growing so that the needs of food, including protein sources, will also increase considerably in the coming years. Animal farming has been related to numerous environmental consequences such as soil erosion, exaggerated water consumption, generation of large quantities of waste and accumulation of greenhouse gases. This is a situation that demonstrates the suitability and importance of finding more sustainable protein alternatives without losing the quality and the nutritional benefits of current common protein sources. In this context, it is worth highlighting the potential of insects and products derived from aquaculture. Particularly, farmed aquatic food products can reduce the impact on wild fish stocks, whose overfishing may end up in an ecological collapse, and insects are easy to be reared and efficient in converting feed into biomass. However, there are still several challenges like the need to adapt technologies and methods for the production and well-characterization of the new ingredients, careful evaluation of the introduction of such new proteins in the diet and its safety of use, including potential allergies, and the acceptance by consumers.

Analysis of drosophila stress resistance at pharmacological inhibition of prostaglandins metabolism

Inhibition of inflammatory processes in the model organisms using non-steroidal anti-inflammatory drugs (NSAIDs) can be an effective geroprotective method. The mechanisms of NSAIDs action in insects have not been studied enough. It is assumed that they are similar to those in mammals and are based on the inhibition of cyclooxygenase 2, which leads to a decrease in the synthesis of prostaglandins. Prostaglandins are central signaling molecules for mediated coordinated cellular immunity of insects and control the imago eclosion, egg production and oogenesis of Drosophila. Obviously, signaling pathways exist where the role of prostaglandins has not yet been shown. In our work, the resistance to starvation of Drosophila melanogaster of wild type stock Canton-S under pharmacological inhibition of prostaglandin metabolism at different stages of ontogenesis was analyzed. In the experiments, nimesulide was used in three different concentrations – 0.1, 0.05, and 0.025 mg/ml. The results of the experiments have shown, that the development of larvae in the medium containing NSAID nimesulide leads to a decrease in resistance to stress factor – starvation on average by 19.2% in females and by 7.4% in males. Resistance to starvation of the most stress-resistant (10% of individuals with the longest life span) females decreases during the development of larvae in the medium containing nimesulide in concentrations 0.1 and 0.05 mg/ml. The consumption of nimesulide by imago at a concentration of 0.025 mg/ml during the first days of life increases stress resistance and life span at starvation in females by 12.4% and in males in all variants of the experiment on average by 17.8%. Under the same experimental conditions, life span during starvation increased in the most stress-resistant females Canton-S. Thus, pharmacological inhibition of prostaglandin metabolism leads to an increase of resistance to starvation if virgin adults are exposed to nimesulide during the first day after eclosion, and stress resistance decreases if nimesulide is consumed by larvae. This is obviously, due to that somatic tissues of the adult flies are almost entirely composed of postmitotic cells, while intensive processes of cell division are characteristic of growing larvae. The data obtained indicate that the action of nimesulide on postmitotic imago cells promotes transition of cells to increased stress tolerance, while the impact on actively dividing cells of larvae leads to a decrease in the resistance of the adults.

Understanding the reproductive biology of Terminalia ferdinandiana for improved fruit yields

Terminalia ferdinandiana Exell., also known as the Kakadu plum, is an important food plant endemic to northern Australia. The fruit has substantial commercial demand as it contains sought-after antioxidants and the greatest concentration of ascorbic acid of any fruit known worldwide. Better knowledge of its reproductive biology is required to increase fruit production from wild stands and sustain commercial demand. Experiments demonstrate that T. ferdinandiana is andromonoecious and self-incompatible, relying on cross-pollination for successful fruit production. Wild stocks of this species are pollen limited, likely caused by pollinator satiation in dense, synchronously flowering stands. These findings indicate that enhanced fruit production requires supplementation of suitable pollinators in wild stands.

Enhancing local fish production through cage aquaculture on the Volta Lake: Impacts on capture fisheries

Aquaculture is a preferred alternative to increasing global fish production than management of wild stocks. Its practice is, however, known to have ecological impacts if not managed well. The study was conducted to determine the potential impact of cage culture of fish on food preference of wild fish. A case study was carried out in the Volta Lake at Kpeve-Tornu using Chrysichthys species which is one of the dominant species found in the Lake. Sampling was done for eight months from August 2013 to March 2014. An area of the lake with no fish farming activities was used as a control. The stomachs of 130 Chrysichthys specimens were analyzed. Importance of each food item was determined using frequency of occurrence method. The dominant food items identified were chironomid larvae and detritus; occurring in 27.3% and 36.4% respectively of the stomach contents at the cage culture site and 63.9% and 52.8% at the control site respectively. Plant parts also occurred in 36.4% of the stomachs at the cage culture site. Lampsilis species, a freshwater mussel, was found only in the stomachs at the control site and it occurred in 41.7% of them. Cage culture in the Volta Lake impacted on the food preference of Chrysichthys species by influencing the availability and abundance of food items. As promising as cage culture is in Ghana; in supplementing production from capture fisheries, it must be done on a scale that keeps its ecological impacts in the Volta Lake in control.

Assessment of Portunus (Portunus) trituberculatus (Miers, 1876) stock in the northern East China Sea

Portunus (Portnus) trituberculatus (Miers, 1876) is one of the important commercial crustaceans in the northern East China Sea. Although extensive research on aquaculture of the species is being carried out, the wild stock is scientifically unassessed. In this paper, the total catch of P. trituberculatus in the northern East China Sea during 2001 and 2015 were classified into 4 carapace width (CW) groups (150 mm), for estimation of the maximum sustainable yield (MSY) and the spawner-recruitment relationships for wild stock and released stock were built, respectively. Standing biomass, spawning biomass and catch were predicted under the assumptions that fishing intensity and quantity of P. trituberculatus released were kept at the levels of those in 2015. The results showed that the MSY of P. trituberculatus is about 14.2×104 t and the corresponding fishing effort (EMSY) is about 14.8×104 tonnage (both the crab pot vessels and trawl vessels were standardised to gillnet vessels). In future, if fishing effort level and the release number equals to those in 2015, the biomass, spawning biomass and catch of P. trituberculatus would remain at 58.9×104 t, 53.1×104 t and 15.6×104 t, respectively. The present stock assessment study was conducted with limited data and further survey data in future may provide more accurate stock assessment to evolve management strategies.

Cryopreservation of sea urchin sperm and early life stages.

Sea urchins are excellent model organisms useful for several lines of biotechnological research. Sea urchins are typically collected from the sea and kept in research facilities all over the world for such purposes. Cryopreservation can be a very powerful tool to enhance the use of sea urchins as a model species for research. The development of cryopreservation protocols for different sea urchin gametes, embryos, and larvae allows year round access to high quality material outside the natural reproductive season. It also reduces the uncertainty and variability that may be caused by changing oceanic, meteorological, and environmental conditions. Access to cryopreserved gametes and embryos will allow using these model organisms in laboratories all around the world, regardless of their facilities or their proximity to a natural population of sea urchins. Cryopreservation is a very useful tool for aquaculture production, fisheries conservation, and wild stock enhancement allowing spat supply all year round without the need of conditioning broodstock for out of season reproduction-which is expensive, time consuming, and often unfruitful. It will also provide flexibility for selective breeding programs by allowing crossings of individuals with different reproductive seasons. Although cryopreservation protocols have been successfully developed for many valuable fisheries species such as sturgeons, salmonid fishes, and other marine invertebrates (e.g., oysters), only a small amount of research has been carried out regarding sea urchin cryopreservation. In this chapter, we outline protocols for the cryopreservation of sea urchin cells.

Early weaning of Atlantic halibut (Hippoglossus hippoglossus) larvae

Atlantic halibut is a cold-water pleuronectiform of the North Atlantic with a high market price and a small wild stock, therefore it has a large potential in farming. However, the halibut is difficult to grow and although work aimed at domestication has been going on since the late 1980ies, there are still only a few commercial farms. The purpose of the present study was to establish a time-point for early weaning of Atlantic halibut larvae, using feed intake as a proxy. First, three commercial diets (Otohime, Gemma Micro and AgloNorse) were compared at 28 days post first-feeding (dpff), with respect to feed intake during 5 days after weaning, using four replicate tanks. The number of larvae per tank out of 28 which had filled guts on the different diets, was 26.7 ± 2.3 (Otohime), 12.0 ± 0.6 (Gemma Micro) and 14.7 ± 1.2 (AgloNorse), respectively. Otohime was chosen for an experiment where feed intake for 5 days after weaning was monitored, starting at 15, 22 and 28 dpff. There was a gradual increase in success with larval age. At 15 dpff the larvae did not eat and there was an almost 100% mortality, at 22 dpff, 12 ± 1 out of 17 larvae survived and 7.3 ± 1.5 had filled guts. At 28 dpff, 14 ± 3 out of 17 larvae survived and all of them had filled guts. The development seems to correlate with the development of larval type digestion. Based on feed intake, successful weaning can be achieved at 28 dpff, however, further studies are needed to determine growth, survival and juvenile quality of Atlantic halibut larvae that have been weaned early on formulated diets.

Male reproductive physiology of Paracentrotus lividus: monthly and seasonal evaluations to study the effects of the environment on gonadal development and sperm cells kinetic

Paracentrotus lividus is a model species for research in different areas, it is also important for modern aquaculture interested in breeding innovative species for greater product diversifications and reduction of the wild stock fishing pressure. This Echinoid was considered a seasonal niche product in the past; nowadays it is highly required on the market for the nutritional characteristics (high protein and low fat) of gonads, the edible part. Our work aims at optimizing farm technics by the study of the habitat impact on P. lividus male reproductive physiology. We correlated environmental variables of the fishing area (temperature, humidity, photoperiod, water temperature, moon phases) to reproductive parameters (morphological gonadal development, sperm cells kinetic). We analyzed data to highlight the relevance, for reproduction, of the length (month or season) of the observations. The significance of this work to the field of aquatic sciences is to drive aquaculture facilities in choosing the desirable period to recover the best spermatozoa with highest total and progressive motility. Moreover setting useful parameters to mimic the best environmental conditions, the highest gonadal development could be reached. This could also promote gametes exchanges between aquaculture facilities in the world taking advantage of the environment dependent gametes maturity.

Genetic and phenotypic differentiation of lumpfish (Cyclopterus lumpus) across the North Atlantic: implications for conservation and aquaculture.

Demand for lumpfish (Cyclopterus lumpus) has increased exponentially over the last decade, both for their roe, which is used as a caviar substitute, and increasingly also as cleaner fish to control sea lice in salmon farming. The species is classified as Near Threatened by the IUCN and there are growing concerns that over-exploitation of wild stocks and translocation of hatchery-reared lumpfish may compromise the genetic diversity of native populations. We carried out a comparative analysis of genetic and phenotypic variation across the species’ range to estimate the level of genetic and phenotypic differentiation, and determined patterns of gene flow at spatial scales relevant to management. We found five genetically distinct groups located in the West Atlantic (USA and Canada), Mid Atlantic (Iceland), East Atlantic (Faroe Islands, Ireland, Scotland, Norway and Denmark), English Channel (England) and Baltic Sea (Sweden). Significant phenotypic differences were also found, with Baltic lumpfish growing more slowly, attaining a higher condition factor and maturing at a smaller size than North Atlantic lumpfish. Estimates of effective population size were consistently low across the North East Atlantic (Iceland, Faroe Islands and Norway), the area where most wild lumpfish are fished for their roe, and also for the aquaculture industry. Our study suggests that some lumpfish populations are very small and have low genetic diversity, which makes them particularly vulnerable to over-exploitation and genetic introgression. To protect them we advocate curtailing fishing effort, closing the breeding cycle of the species in captivity to reduce dependence on wild stocks, restricting the translocation of genetically distinct populations, and limiting the risk of farm escapes.

Identification and adaptability of hatchery-origin Japanese flounder released into the Bohai Sea after the summer fishing moratorium

Because the artificial cultivation environment differs from the natural habitat of the Bohai Sea, it is essential to study the adaptability of hatchery-reared juveniles released into this area. Hatchery-origin Paralichthys olivaceus stocks were identified via morphological observation and genetic tags (i.e., mitochondrial DNA and microsatellites). Seven genomic microsatellite loci with a high PIC (polymorphic information content, 0.885–0.945) and a high exclusion probability (0.930–0.981) were selected and arranged into two multiplex PCRs. In total, 46.75% of the captures were assigned to our broodstocks. There were no significant differences in genetic diversity, such as Ar (allelic richness, P = .754) and He (expected heterozygosity, P = 0. 658), among the hatchery-origin stock (HS), their parents (P), the wild stock (WS) and the captured broodstocks (CB) in 2016. However, losses of Ar in the HS indicated that more attention should be given to the number of broodstocks in a reared population. The overall genetic divergence among these four groups was low (FST = 0.005), and the results of AMOVA also showed no genetic differences among them (P = .500), indicating that no pronounced genetic differentiation was found following the stock enhancement program in the Bohai Sea. There was no significant difference between HS and WS in terms of growth parameters (P > .05) and feeding ecology (P > .05). Furthermore, the stomach contents of the two groups were basically identical and consisted mainly of fish. Therefore, overall, the hatchery-origin juveniles had already adapted to the natural area after the summer fishing moratorium.