Lake survival of hatchery and pre-stocked pond brown trout, Salmo trutta L.

Abstract. A comparison was made of lake survival, after 2 years, of hatchery and pre-stocked pond brown trout, Salmo trutta L., (age 0+) in two small mountain lakes in south-central Norway, one which contained a resident population of brown trout. There was a significantly higher recapture of pond fish in both lakes. The mortality rate for the stocked fish was significantly higher in the lake which contained a resident population of brown trout. The competitiveness of the stocked fish is discussed in relation to foraging success, predation and stress.     

Recapture of pond- and hatchery-reared brown trout, Salmo trutta L., released in small streams

Abstract. Two groups of 0+ brown trout, Salmo trutta L., one pond-reared and one hatchery-reared (fish length 32-80mm), were released in eight small streams in three different areas of Norway between 1984 and 1987. Hatchery and pond fish were reared at different sites, but releases were made both near the rearing site and in the home area of the other group. A total of 2550 fish were recaptured by electrofishing the year after stocking. We found great variations in the recapture rates of pond and hatchery fish in one stream between years, and between streams in different areas the same year. These results indicate that the rearing method is not essential to the recapture rate. Both pond and hatchery fish generally had higher recapture rates in streams near their rearing site than in the distant areas. Thus factors associated with transportation seem to influence the survival of stocked fish. The results also indicate that size at stocking may be an important factor for the recapture rate.     

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.     

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.     

Stranding of pond- and hatchery-reared juvenile brown trout, Salmo trutta L., during draw-down of a pond

Abstract. One thousand each of pond and hatchery reared 0+ brown trout, Salmo trutta L., were fin-clipped and released in a 1300-m² large earthen pond. The pond was drawn down 5 days after the introduction, and descending individuals were caught in a trap at the outlet. A total of 904 pond-reared and 890 hatchery-reared fish were recaptured, i.e. a loss of 9·6 and 110% respectively, A total of 25 pond-reared and 16 hatchery reared fish were recorded stranded in the pond during the draw-down, accounting for 2·7 and 1·8% of total recoveries.
Pond-reared fish descended significantly earlier than did hatchery fish. Most individuals descended during the first 4·5h (75-83%). However, the final recoveries were made 10 days (233h) after the first descent.     

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.     

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.     

Evaluation of Three Feeds for Hatchery Rearing Channel Catfish Fry

Two 7 day feeding trials were conducted with channel catfish swim-up fry to evaluate growth, feed conversion ratio, and body composition of fish fed one of the following feeds: salmon starter, catfish starter, or trout starter. Fish fed the salmon or trout starter feeds gained 50–75% more weight, converted feed more efficiently, and had higher body fat stores than fish fed the catfish starter feed. This may be related to the higher protein and energy content of these two feeds. It may be advantageous to feed salmonid starter feeds to hatchery reared catfish fry; however, it is not known whether or not the improved performance observed in the hatchery continues once the fish are stocked into nursery and grow out ponds.     

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.     

Post-stocking Movements and Recapture of Hatchery-reared Trout Released into Flowing Waters - Effect of a Resident Wild Population

The post-stocking movements and survival of hatchery-reared brown trout (Salmo trutta L.) (length 18–19 cm) stocked into depopulated and control stretches of the Afon Clettwr, South Wales, were investigated. Data were obtained from electrofishing surveys and rewarded tag returns. Recapture rates ranged from 67–76% for both stretches. The resident population of wild brown trout had no significant effect on the dispersion of the stocked fish, the majority of which remained close to the point of stocking. No stocked fish were recovered from the experimental stretches in the year following their introduction. Within one year the depopulated stretch had been recolonized by wild trout. The implications upon restocking after a fish kill are discussed.     

Stocking of brown trout, Salmo trutta L.: effects of acclimatization

One-year-old hatchery brown trout, Salmo trutta L., ( n  = 16 520) from a sea-run, local brood stock were marked and released (scatter-planted) into the River Laisälven in northern Sweden. Eight different groups were created using Alcian blue and Visible Implant Elastomer tags. Half the fish were kept in small enclosures in four stocking areas for 6 days before release. The other half were released just after transportation. To evaluate the effect of acclimatization on post-stocking performance, the areas were electric fished 2 months later. During the electric fishing survey, a higher number of the acclimatized hatchery fish were recaptured than those released immediately. The growth rate of stocked fish differed significantly between stocking areas and fish held in enclosures grew more than those released directly. The rate of recapture of hatchery fish varied between stocking areas (6.4–17.4%). Movements of juveniles within and between the stocking areas were low, and only 3.6% of the recaptured fish were found in an area not originally stocked. These results showed that acclimatization of fish before release increases the number and size at recapture within a stocking area.     

Otter (Lutra lutra) predation on stocked brown trout (Salmo trutta) in two Danish lowland rivers

Abstract –  This study aimed to evaluate otter predation on stocked trout. Large hatchery-reared trout (16–30 cm) were stocked into two Danish rivers with different fish populations. Otter diet before and after trout stocking was determined by analysing 685 spraints, collected regularly during the 35-day study period. Fish composition in the rivers before stocking was assessed by electrofishing. In River Trend, a typical trout river, the proportion of trout in the otter diet increased from 8% before stocking to 33% a few days after stocking. Moreover, trout lengths in the diet changed significantly towards the lengths of stocked trout, indicating that newly stocked trout were preferred to wild trout. In River Skals, dominated by cyprinids, there was no change in otter diet after stocking of hatchery trout, i.e., these were ignored by otter. Otter predation should be taken into account together with fish and bird predation, when stocking is used as a measure for conserving endangered salmonid populations.     

Experimental studies on planting artificial stream channels with unfed and six weeks fed salmon (Salmo salar L.) and trout (S. trutta L.) fry/parr

Abstract– Experimental comparisons were made between release as unfed fry and release as six weeks fed parr, upon the growth and final population density of young salmon and trout over a ten week period. Salmon and trout released into experimental channels as unfed fry at densities of about 19 fish. m^-2 showed rapid reduction in numbers, chiefly by downstream dispersal, accompanied by negligible growth. After substantial reduction in numbers, there was a reduced rate of dispersal and rapid growth. Salmon and trout retained in a hatchery at high density (80 to 200 fish. m^-2) and fed for six weeks on proprietary food showed slow, but measurable, growth. After release into the channels these fish adjusted their numbers, mainly by downstream dispersal, and showed an increased growth rate. At the end of a ten week period, salmon introduced as fed parr had approximately twice the population density of salmon introduced as unfed fry. No similar difference in population density could be shown for trout. For both species, the fish introduced as fed parr had a lower mean weight after ten weeks than had the fish introduced as unfed fry.     

The future of stock enhancements: lessons for hatchery practice from conservation biology

The world's fish species are under threat from habitat degradation and over‐exploitation. In many instances, attempts to bolster stocks have been made by rearing fish in hatcheries and releasing them into the wild. Fisheries restocking programmes have primarily headed these attempts. However, a substantial number of endangered species recovery programmes also rely on the release of hatchery‐reared individuals to ensure long‐term population viability. Fisheries scientists have known about the behavioural deficits displayed by hatchery‐reared fish and the resultant poor survival rates in the wild for over a century. Whilst there remain considerable gaps in our knowledge about the exact causes of post‐release mortality, or their relative contributions, it is clear that significant improvements could be made by rethinking the ways in which hatchery fish are reared, prepared for release and eventually liberated. We emphasize that the focus of fisheries research must now shift from husbandry to improving post‐release behavioural performance. In this paper we take a leaf out of the conservation biology literature, paying particular attention to the recent developments in reintroduction biology. Conservation reintroduction techniques including environmental enrichment, life‐skills training, and soft release protocols are reviewed and we reflect on their application to fisheries restocking programmes. It emerges that many of the methods examined could be implemented by hatcheries with relative ease and could potentially provide large increases in the probability of survival of hatchery‐reared fish. Several of the necessary measures need not be time‐consuming or expensive and many could be applied at the hatchery level without any further experimentation.     

Genetic effects of introduced hatchery stocks on indigenous brown trout (Salmo trutta L.) populations in Spain

Abstract– To assess the levels of gene introgression from cultured to wild brown trout populations, four officially stocked locations and four nonstocked locations were sampled for one to three consecutive years and compared to the hatchery strain used for stocking. Allozyme analysis for 25 loci included those previously described as providing allelic markers distinguishing hatchery stocks and native populations. Different levels of hybridization and introgression with hatchery índividuals were detected in stocked drainages as well as in protected locations. These findings indicate that new policies for stocking and monitoring hatchery fish are needed if gene pools of wild Spanish brown trout populations are to be preserved.     

The effects of ration size on migration by hatchery‐raised Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)

Abstract – The possibility to increase the proportion of migrating hatchery‐reared smolts by reducing their food ration was studied. Lake‐migrating, hatchery‐reared salmon (Salmo salar) and trout (Salmo trutta) smolts were either fed normal rations, based on recommendations from the fish‐farming industry, or reduced (15–20%) rations. They were released into the River Klarälven, western Sweden, and followed as they swam downstream to Lake Vänern, a distance of around 25 km. For both Atlantic salmon and brown trout, smolts fed a reduced ration migrated faster than fish fed a normal ration. Furthermore, a higher proportion of salmon smolts fed reduced rations migrated to the lake than fish fed normal rations in 2007 but not in 2006. This difference between years corresponded to greater treatment differences in size and smolt status in 2007 than in 2006. For trout, the proportion of migrating individuals and smolt development did not differ with ration size. Trout migrants fed a normal ration had a higher standard metabolic rate (SMR) than nonmigrants, whereas there was no difference in SMR between migrating and nonmigrating salmon. These results show that it is possible to use a reduced food ration to increase the migration speed of both Atlantic salmon and brown trout and to increase the proportion of migrating Atlantic salmon.     

Effect of Density at Harvest on the Growth Performance and Profitability of Hatchery‐reared Spotted Rose Snapper,Lutjanus guttatus,Cultured in Floating Net Cages

This study evaluated the effect of the density at harvest on the performance and profitability of hatchery‐reared spotted rose snapper cultured in cages. The fish were stocked at harvest densities of 15, 20, and 22 kg/m³ in cages of 222 and 286 m³. More than 39,000 snapper fingerlings with an initial weight of 14 g were stocked. The fish were fed an extruded diet and cultured over a 360 d period. The thermal growth coefficient ranged from 0.04 to 0.05 and survival was 95% for all treatments, with the highest final weight (436.8 g) observed for fish reared at a density of 20 kg/m³. The allometric value b indicated that hatchery‐raised, cage‐cultured snapper were heavier than their wild counterparts. The major costs were feed (ranging from 44.7–45.9%), labor (22.4–32.6%), and seed costs (20.2–26.1%). The total production cost ranged from US$ 6.5 to US$ 7.5/kg. The baseline scenario was not economically feasible. However, a 10% increase in the sales price resulted in increases in the internal rate of return (183%) and net present value (US$ 97,628.9). These results suggest that L. guttatus has the potential for commercial production in cages.     

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.     

Feeding by hatchery-reared and wild brown trout, Salmo trutta L., in a Norwegian stream

Abstract. Hatchery-reared brown trout, Salmo trutta L., yearlings were captured shortly (3h to one week) after their release in a Norwegian stream. The feeding of recaptured hatchery fish was compared with that of wild brown trout. The investigations were carried out during three different periods (May, July and October). Investigations of drift fauna indicated that food availability was best in May. Most hatchery-reared brown trout started feeding shortly after their release in all three periods. Hatchery fish went through a learning process with respect to feeding. This was most clearly demonstrated by the amounts of plant fragments in their stomachs, which were always greater in hatchery fish than in wild fish but which decreased with time after release in hatchery fish stomachs in all three periods. By about a week after release, hatchery trout appeared to be feeding on wild prey nearly as well as did wild fish, but they achieved this better in May than in October.