Antipredator responses to overhead fright stimuli in hatchery-reared and wild European sea bass (Dicentrarchus labrax L.) juveniles

In this study, shoals of hatchery‐reared and wild sea bass juveniles (Dicentrarchus labrax L.) were tested for differences in their antipredator responses towards a visual (shadow) and a mechanical (dummy bill) overhead stimulus. Two behavioural variables – distance from the bottom and freezing duration – were measured during post‐stimulus phases of each test and compared between wild and hatchery‐reared shoals, composed of 10 juveniles each. The results showed that in both hatchery‐reared and wild juveniles, stimulus exposure elicited a significant decrease in the mean shoal distance from the bottom. Similarly, individuals from both groups engaged a freezing reaction, but the mean freezing duration was significantly higher in wild‐ than in hatchery‐reared juveniles. Results are discussed in the light of their relevance for the enhancement of restocking programmes.     

The Effects of Live and Artificial Diets on Feeding Performance of Cultured Winter Flounder,Pseudopleuronectes americanus,in the Wild: Survival,Feeding, Growth,and Nucleic Acid Analyses

This research, which is part of a larger study designed to assess the feasibility of winter flounder, Pseudopleuronectes americanus, stock enhancement in New Hampshire, identifies hatchery feeds that optimize feeding‐related performance of fish once released in the wild. Fish reared on post‐nauplii of brine shrimp, Artemia sp., white worms, Enchytraeus albidus, common burrower amphipods, Leptocheirus plumulosus, and formulated pellets were evaluated post‐release from in situ cages using survival, growth rate, feeding onset and incidence, stomach fullness, diet composition, and nucleic acid‐based condition as indicators of hatchery diet suitability. Amphipod‐reared fish had the highest mean stomach content index of all feed types, including wild fish. Wild and worm‐reared fish exhibited the most similar survival, overall stomach fullness, and diet composition profiles over time. Amphipod‐reared fish ranked highest in overall performance; however, if wild fish performance is viewed as the ideal for a stocked fish, worm‐reared fish performed optimally. This study describes hatchery feeding strategies that may ease the transition of flatfish released into the wild for stock enhancement.     

An evaluation of the contribution of hatchery stocking on population density and biomass: a lesson from masu salmon juveniles within a Japanese river system

Stocking is an important management tool for enhancing fisheries resources, but its actual contribution to fisheries resources is controversial, taking into consideration both the positive and negative effects. This study compared density and biomass of hatchery (otolith thermal marked) and wild masu salmon parr between stocked and unstocked rivers to evaluate the contribution of stocking with hatchery‐reared fish. Density and biomass of all fish did not differ between stocked and unstocked rivers. Moreover, density and biomass of wild fish in the stocked rivers were lower than those of the unstocked rivers. Density and biomass of hatchery fish in a non‐natural reproducing river were similar with those of all fish in natural reproducing rivers. These results indicate that hatchery stocking does not have positive effects on population density or biomass but replaces wild fish with hatchery fish and that non‐natural reproducing areas are more suitable as stocking sites.     

Economic,ecological and genetic impacts of marine stock enhancement and sea ranching: A systematic review

Hatchery release is one of the most popular management tools in fisheries, forestry and wild life management, while its negative impacts on wild populations are a global concern. Research and monitoring of its impacts are generally lacking, and the usefulness of hatchery release for fisheries and conservation objectives is unclear. Here, I evaluated positive and negative impacts of worldwide marine stock enhancement and sea ranching programmes in a systematic review associated with meta‐analyses with the goal of reducing bias of the review. Vast numbers of individuals of more than 180 species are released into the wild each year, but most studies are at experimental stages to assess its potential, and empirical studies are sparse for evaluating the impact on fishery production. Most cases are economically unprofitable except for a few successful cases or unevaluated. The effects of releasing juveniles can be dwarfed by the magnitude of natural recruitment when the spawning stock produces much larger recruitment than released juveniles. Density‐dependent growth caused by competition of food can be substantial, and growth rates of hatchery and wild fish and other competitive species can simultaneously be reduced when stocking exceeded the carrying capacity. Relative reproductive success can vary depending on the species, seed quality and environmental factors. Empirical studies show evidence of substantial gene flow from hatcheries, but fitness reduction in stocked populations has not been reported. The results represent the current state of worldwide marine stock enhancement and sea ranching activity and provide key information for growing fields of artificial propagation and conservation.     

Wild origin and enriched environment promote foraging rate and learning to forage on natural prey of captive reared Atlantic salmon parr

Abstract – After release to the wild, captive reared salmon have shown lower foraging rates on natural prey and impaired ability to avoid natural predators and thus lower survival compared with wild‐born conspecifics. Here, we examine whether captive breeding influences learning of foraging on natural prey and how enriched rearing methods may improve foraging on natural prey by Atlantic salmon (Salmo salar) parr. We reared offspring of hatchery or wild salmon of the same population in either a standard or enriched environment at production‐scale densities. The enriched environment featured submerged overhead shelter, varying water current, depth and direction and consequently alterations in food dispersion. Parr reared in the enriched environment expressed higher feeding rates, and parr of wild origin started to forage earlier on natural prey. The enriched method promoted foraging of hatchery reared parr on natural prey and is easily applicable to commercial production of salmonids for reintroduction or stock enhancement purposes.     

Efficacy of fluorescent calcein mark retention and identification in endangered Colorado pikeminnow Ptychocheilus lucius

Distinguishing hatchery‐reared fishes from wild conspecifics can be required to quantify the success of augmentation programmes. This study estimated the probability of identifying calcein‐marked, hatchery‐reared Colorado pikeminnow Ptychocheilus lucius Girard from external and internal structures. Both control and marked fish held in the laboratory were correctly identified 80% of the time after 300 days. A fluorometer was more accurate 180 days post‐marking, whereas visual observation was more discriminating at 300 days. There were no differences in detection rates among structures in laboratory fish, and for most structures of fish held outdoors, detection rates were <20%. Overall, a strong negative effect of light on mark persistence was observed. Also, an initial positive effect of fish size on mark fluorescence and a negative effect of fish growth were detected. These results suggest the potential use of calcein as a batch‐marking tool would be aided by future studies that better quantify light exposure and calcein mark persistence in both field and experimental settings.     

Behaviour and survival of wild versus stocked fingerling walleye

Walleye Sander vitreus Mitchill have been progressively raised in hatcheries to larger sizes under the paradigm that larger stocked fish have higher survival. However, extended time in hatcheries may result in domestication, with stocked individuals lacking behaviours that promote survival. The objective of this study was to evaluate behaviour and survival of wild versus stocked fingerling (>200 mm) walleye in two Iowa reservoirs. Radio telemetry was used to evaluate walleye movement rates, depth use, home range size, habitat selection and apparent survival. Depth use increased with days since stocking and varied between lake‐years but was similar between walleye groups. Daily movement rates varied by the interaction between group and day, with rates declining through time. Home ranges did not differ between groups but were significantly greater in Big Creek than Brushy Creek. Walleye in both lakes generally used habitat in proportion to availability, with few differences between groups detected. Weekly apparent survival ranged from 0.948 to 1.000, varied across lakes, years and seasons, and was higher for stocked than wild walleye in Big Creek but not Brushy Creek. The results indicate that hatchery‐reared fingerling walleye behave similar to but can have higher survival than wild fish, suggesting that domestication may not be occurring and that stocking autumn fingerling walleye may help supplement year‐class strength.     

Increased harvest of anadromous hatchery steelhead,Oncorhynchus mykiss (Walbaum), through return timing manipulation

Harvest hatchery programmes serve to augment fisheries but should also minimise impacts to wild populations. In an experiment to increase harvest in an anadromous hatchery steelhead, Oncorhynchus mykiss (Walbaum), terminal river fishery, a new hatchery strain, was created using selective breeding of early arriving adults to the river. First‐generation progeny of the new early arriving strain were reared and released over 4 years concurrent with releases of the standard hatchery strain. This study compares adult return timing, terminal harvest and straying behaviour of progeny of the early arriving and standard hatchery strains. The new strain migrated towards the terminal river fishery earlier, they were harvested earlier in the eight‐month fishing season and their overall harvest was 17% greater, but 7.7% of the new strain strayed to other rivers compared to 5.0% of the standard strain. Selective breeding to match adult return timing with fishing effort may help bolster harvest, but a paired release evaluation, such as was conducted in this study, would be prudent before switching all hatchery production to a selectively bred strain.     

Survival and growth of hatchery and wild brown trout (Salmo trutta) parr in three Austrian headwater streams

Brown trout populations of three headwater streams in the Northern Limestone Alps of Austria were supplemented by three‐month‐old hatchery‐reared parr from a wild and locally adapted strain and a nonresident domesticated hatchery strain. Growth and survival were monitored with three surveys over a period of 16 months after stocking. Fish descending from the wild reared origin strain demonstrated higher survival rates than the hatchery strain. Differences in growth were found among the investigated streams but not among the investigated strains. The differing temperature regimes of the streams were considered as the primary factor causing those disparities. We conclude that stocking measures had little or no additive effect on successful natural reproduction, as the resident wild brown trout performed significantly better than the stocked fish.     

Failure of predator conditioning: an experimental study of predator avoidance in brown trout (Salmo trutta)

Many studies have documented that hatchery‐reared salmonids generally have inferior survival after being stocked compared with wild conspecifics, hatchery and wild salmonids have been observed to differ in their antipredator responses. The response of brown trout (Salmo trutta) juveniles (0+) of differing backgrounds to a live predator was compared in two experiments. First, the antipredator behaviour of predator‐naïve hatchery‐reared brown trout and wild‐exposed brown trout were assessed in behavioural trials which lasted for eight days. Second, predator‐naïve and predator‐conditioned hatchery‐reared brown trout were assessed in identical behavioural trials. Brown trout were ‘predator‐conditioned’ by being held in a stream‐water aquarium with adult Atlantic salmon (Salmo salar) and adult brown trout for two days prior to behavioural trials. Predator‐conditioned hatchery‐reared brown trout spent more time in shelters in the trial aquaria than predator‐naïve hatchery‐reared fish, but did not differ in time spent in the predator‐free area. Predator conditioning may account for the increased time spent in the shelter, but does not appear to have affected time spent in the predator‐free area. However, even if significant alteration in behaviour can be noted in the laboratory, the response might not be appropriate in the wild.     

Comparative performance of hatchery-reared and wild Scylla paramamosain (Estampador, 1949) in pond culture

The performance of hatchery‐reared juveniles either in aquaculture grow‐out systems or stock enhancement is likely to be dependent on a range of factors during the hatchery phase of production. With recent progress in the development of hatchery systems for the mud crabs Scylla spp., there is growing interest in evaluation of the quality of hatchery‐reared juveniles relative to wild seed crabs as currently used in aquaculture. Hatchery‐reared and wild‐collected Scylla paramamosain juveniles were stocked either together in ponds or separately. All crabs were tagged with microwire‐coded tags, so that origin could be determined in the mixed groups. Preliminary validation demonstrated that tagging did not affect survival or growth, with a tag retention of 94%. After 106 days of culture, there was no significant difference in survival at harvest between the two sources of crabs. The wild juvenile crabs had a significantly higher initial weight:carapace width (CW) ratio compared with those from the hatchery, indicating a difference in condition. However, where crabs were stocked separately, the hatchery‐reared animals exhibited significantly faster growth than those collected from the wild, both in terms of specific growth rate and CW increase per month. However, in the mixed ponds, where there was competition with wild crabs, there was no significant difference in growth rate between crabs from the two sources. Overall, the results demonstrate that the growth performance of hatchery‐reared S. paramamosain can at least equal that of wild‐collected seed crabs in ponds culture.     

Interspecific competition between restocked 0+ salmon parr (Salmo salar) and native fish species in a large European river

Atlantic salmon populations have experienced strong declines in most large European rivers. In the Loire Basin, France, a major restocking effort has been carried out on the Allier River to reduce the wild population decline. This study aimed at investigating the trophic insertion of hatchery‐reared salmon parr and whether they compete for resources with native fish species. For this purpose, two riffles located in the upstream and downstream parts of the restocked area have been surveyed monthly following the initial 0+ salmon fry release. 0+ parr densities remained high upstream, with autumnal values greater than those recommended to maximise smolt production. In contrast, downstream densities declined to weak values despite a faster increase in size, probably mainly due to summer temperatures rising above the discomfort threshold. By analysing the vulnerability to predation of ingested invertebrate prey, we highlighted the role of habitat constraints in driving most of the different fish species to a likely opportunistic utilisation of available food resources. As a result, species such as stone loaches and barbel juveniles exhibited narrow trophic niches and high overlaps with 0+ parr. Nonetheless, both abundant prey resources and spatial or temporal habitat segregation have limited interspecific competition, enabling competitive coexistence of sympatric species, except for barbel juveniles in certain circumstances. Therefore, our findings suggest that future restocking programmes should carefully consider the thermal and hydraulic conditions regarding further smolt production as well as their general trophic context, according to the potential inconvenience of restocked salmon fry arrival relative to native species.     

Effects of transportation timing on osmoregulation and survival in yearling hatchery Chinook salmon (Oncorhynchus tshawytscha)

Seasonal timing of transportation and acclimation of juvenile Chinook salmon (Oncorhynchus tshawytscha) between hatcheries may affect osmoregulation and survival. We investigated the duration of time fish need to acclimate to hatchery conditions prior to being presented with a saltwater challenge. We monitored acute survival and osmoregulatory ability following a 24-h saltwater challenge of fish previously transported to a hatchery at various times throughout the year compared to fish reared at that hatchery. Fish that underwent a saltwater challenge 3 weeks after transport had significantly reduced osmoregulatory performance and increased mortality compared to fish allowed an acclimation period of 2 months.     

Completion of the Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel) life cycle

Tuna aquaculture is currently dependent on the wild capture of juveniles for production. The development of hatchery technology for bluefin and other tunas would be a major step forward in improving sustainability of their aquaculture. The present study overviews the technology in the life cycle completion of the Pacific bluefin tuna (PBT) Thunnus orientalis (Temminck et Schlegel) under aquaculture conditions in Kinki University, and the problems to be solved for the establishment of tuna hatchery technology. On 23 June 2002, broodstock of PBT that were artificially hatched and reared spontaneously spawned in captivity. The resulting eggs hatched and were subsequently reared to the juvenile stage. The spawning fish were the result of a research project started in 1987 to rear wild‐caught juvenile PBT that were several months old. Fertilized eggs were obtained from these fish in 1995 and 1996. Resulting juveniles (the artificially hatched first generation) were reared to maturity and spawned in 2002. Over the summer of 2002, 1.63 million eggs from these fish were used for a mass rearing experiment, and 17 307 juveniles were produced and transferred to an open sea net cage. Of these artificially hatched second‐generation PBT, 1100 grew to approximately 95 cm total length and 14 kg body weight in 22 months. This procedure means the completion of PBT life cycle under aquaculture conditions, which was first attained among large tuna species. The problems awaiting solution in PBT hatchery production are their unpredictable spawning in captivity, to improve survival during the first 10 days post hatch, to reduce cannibalism in larval and juvenile stages, and to solve collision problem causing high mortality during the juvenile stage.     

Do predators,handling stress or field acclimation periods influence the survivorship of hatchery‐reared abalone Haliotis kamtschatkana outplanted into natural habitats?

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Comparison of the distribution and homing of hatchery-reared and wild Atlantic salmon,Salmo salar L., from north-east England

Hatchery-reared Atlantic salmon, Salmo salar L., parr and wild smolts which were microtagged and released into rivers in north-east England were recaptured by the fisheries at West Greenland, Faroes and on the Irish west coast, by the homewater net fisheries and by rod fisheries in rivers in north-east England. No significant differences were observed in the patterns of exploitation of hatchery-reared and wild fish in the distant water fisheries. The distribution of tag recoveries in coastal waters was strongly influenced by the pattern of fishing effort which was concentrated in the middle of the fishery area, but recaptures tended to be biased towards the river of release. There were significant differences in the distribution of recaptures of fish released in different rivers and between hatchery-reared and wild fish from the River Wear. There were also differences in the timing of recaptures of hatchery and wild fish from this river in the coastal net fishery. Very few fish were recaptured in rivers other than the one in which they were released, and there was no significant difference between straying rates for hatchery and wild fish. The relative numbers of recaptures in the coastal fishery and in the home river was the same for translocated hatchery fish and wild fish, thus refuting the suggestion that hatchery-reared fish have a reduced ability to home. The distribution of recaptures within fresh water provides clear evidence of tributary-specific homing of hatchery-reared fish.     

Size‐dependent stress response in juvenile Arctic charr (Salvelinus alpinus) under prolonged predator conditioning

Predator conditioning can be used to improve post‐release antipredator recognition of hatchery‐reared salmonids. However, possible negative stress‐related effects of prolonged predator conditioning on juvenile fish physiology are poorly understood. We studied the effects of prolonged (91 days) predator odour exposure on whole‐body cortisol level and spleen size in six full‐sib families of juvenile hatchery‐bred Arctic charr (Salvelinus alpinus). Chemical cues from water containing charr‐fed pikeperch (Sander lucioperca) were used as the predator exposure stimuli and lakewater was used as a chemical control. Our study revealed that juvenile body cortisol levels post‐predator conditioning were affected by treatment, fish size and their interaction. Importantly, among the smaller (i.e. slowest growing) charr, the predator‐exposed fish had higher cortisol levels than control fish, while the opposite pattern was true for the larger fish. These results suggest that chemical cues from charr‐fed predators induce a prolonged stress response in juvenile charr. As prolonged predation exposure seems to elevate stress levels in a size‐dependent manner, the larger, faster growing fish could possibly have intrinsically lower stress responses to predation threats than smaller, slower growing fish. Possible coupling between stress sensitivity and growth requires further attention due to the likely implications for the management of unintended domestication among captive‐reared salmonids.     

The effect of physiological and environmental conditions on smolt migration in Atlantic salmon Salmo salar

Hydropower development has negatively influenced Atlantic salmon (Salmo salar) populations. Compensatory hatchery‐rearing programmes exist, but released fish suffer from high mortality that may be related to the lack of experience from natural environments in hatchery‐reared smolts and their large body size and high energetic state. Here, we used acoustic telemetry to test how body size, energetic state, and the environmental conditions of the river affect migration in hatchery‐reared smolts. The study was conducted in three consecutive years between 2011 and 2013 in the lower part of the River Umeälven, Sweden. For individual fish, there was no effect of body size but the energetic state of the fish had a negative effect on sea entry. The most important factor affecting sea entry rate was the water discharge in the old river bed that differed among years. Smolts were more likely to enter the sea in years when the discharge was high or when the discharge increased substantially shortly after release. Hatchery‐reared fish had higher migration speed at a slower flowing section compared with a faster flowing section, which was likely a result of large hesitation to enter the rapid section. The increase in water discharge led to an increase in fish migration speed disproportional to the increase in water velocity. Our results highlight the importance of water discharge for the smolts during smolt migration, and we argue that concern should be given to migrating fish when managing regulated rivers.     

Predation on wild and hatchery salmon by non‐native brown trout (Salmo trutta) in the Trinity River,California

Non‐native predators may interfere with conservation efforts for native species. For example, fisheries managers have recently become concerned that non‐native brown trout may impede efforts to restore native salmon and trout in California's Trinity River. However, the extent of brown trout predation on these species is unknown. We quantified brown trout predation on wild and hatchery‐produced salmon and trout in the Trinity River in 2015. We first estimated the total biomass of prey consumed annually by brown trout using a bioenergetics model and measurements of brown trout growth and abundance over a 64‐km study reach. Then, we used stable isotope analysis and gastric lavage to allocate total consumption to specific prey taxa. Although hatchery‐produced fish are primarily released in the spring, hatchery fish accounted for most of the annual consumption by large, piscivorous brown trout (>40 cm long). In all, the 1579 (95% CI 1,279–1,878) brown trout >20 cm long in the study reach ate 5,930 kg (95% CI 3,800–8,805 kg) of hatchery fish in 2015. Brown trout predation on hatchery fish was ca. 7% of the total biomass released from the hatchery. Brown trout only ate 924 kg (95% CI 60–3,526 kg) of wild fish in 2015, but this was potentially a large proportion of wild salmon production because wild fish were relatively small. As large brown trout rely heavily on hatchery‐produced fish, modifying hatchery practices to minimise predation may enhance survival of hatchery fish and potentially reduce the abundance of predatory brown trout.