Unfed Fry Research Articles

Modulations of lipid metabolism and development of the Atlantic salmon (Salmo salar) fry in response to egg-to-fry rearing conditions.

In stocking program, the use of artificial incubation conditions in hatcheries from the fertilisation of eggs to the release of unfed fry could reduce their ability to adapt to the natural environment. This study evaluates the effects of three factors on the fitness and physiology of salmon fry at their emergence, the origin of water (river vs drilling), the type of support in the incubator (support matrix vs plastic sheets) and the type of incubators (Californian vs vertical trays), and compares them to a semi-natural incubation method in river. Key biological functions including nutritional and immune status were compared among experimental conditions using biometric parameters, lipid composition and gene expression analyses. Our findings demonstrated that fry incubated in vertical trays supplied with river water had no significant difference in growth and lipid composition compared to those in semi-natural incubators. Besides, fry incubated on a substrate matrix in Californian trays exhibited phenotypic characteristics closest to those incubated in river. This support matrix improved fish growth, lipid consumption and distribution compared to fry on plastic sheets. Moreover, the large amounts of several PUFAs in these fry could allow a better membrane fluidity ensuring a better adaptation to temperature variation under cold conditions. In addition, drilling water improved the survival rate compared to river water due to lower numbers of fine particles, known to be responsible for the clogging of eggs. To conclude, using a substrate combined with drilling water in artificial incubators could increase fry fitness and its adaption to wild life.

Reduced fitness of Atlantic salmon released in the wild after one generation of captive breeding

Salmonids rank among the most socioeconomically valuable fishes and the most targeted species by stocking with hatchery-reared individuals. Here, we used molecular parentage analysis to assess the reproductive success of wild- and hatchery-born Atlantic salmon over three consecutive years in a small river in Québec. Yearly restocking in this river follows a single generation of captive breeding. Among the adults returning to the river to spawn, between 11% and 41% each year were born in hatchery. Their relative reproductive success (RRS) was nearly half that of wild-born fish (0.55). RRS varied with life stage, being 0.71 for fish released at the fry stage and 0.42 for fish released as smolt. The lower reproductive success of salmon released as smolt was partly mediated by the modification of the proportion of single-sea-winter/multi-sea-winter fish. Overall, our results suggest that modifications in survival and growth rates alter the life-history strategies of these fish at the cost of their reproductive success. Our results underline the potential fitness decrease, warn on long-term evolutionary consequences for the population of repeated stocking and support the adoption of more natural rearing conditions for captive juveniles and their release at a younger stage, such as unfed fry.

Reduced reproductive success of hatchery coho salmon in the wild: insights into most likely mechanisms

Supplementation of wild salmonids with captive-bred fish is a common practice for both commercial and conservation purposes. However, evidence for lower fitness of captive-reared fish relative to wild fish has accumulated in recent years, diminishing the apparent effectiveness of supplementation as a management tool. To date, the mechanism(s) responsible for these fitness declines remain unknown. In this study, we showed with molecular parentage analysis that hatchery coho salmon (Oncorhynchus kisutch) had lower reproductive success than wild fish once they reproduced in the wild. This effect was more pronounced in males than in same-aged females. Hatchery spawned fish that were released as unfed fry (age 0), as well as hatchery fish raised for one year in the hatchery (released as smolts, age 1), both experienced lower lifetime reproductive success (RS) than wild fish. However, the subset of hatchery males that returned as 2-year olds (jacks) did not exhibit the same fitness decrease as males that returned as 3-year olds. Thus, we report three lines of evidence pointing to the absence of sexual selection in the hatchery as a contributing mechanism for fitness declines of hatchery fish in the wild: (i) hatchery fish released as unfed fry that survived to adulthood still had low RS relative to wild fish, (ii) age-3 male hatchery fish consistently showed a lower relative RS than female hatchery fish (suggesting a role for sexual selection), and (iii) age-2 jacks, which use a sneaker mating strategy, did not show the same declines as 3-year olds, which compete differently for females (again, implicating sexual selection).

Ontogenetic selection on hatchery salmon in the wild: natural selection on artificial phenotypes.

Captive rearing often alters the phenotypes of organisms that are destined for release into the wild. Natural selection on these unnatural phenotypes could have important consequences for the utility of captive rearing as a restoration approach. We show that normal hatchery practices significantly advance the development of endangered Atlantic salmon (Salmo salar) fry by 30+ days. As a result, hatchery fry might be expected to face strong natural selection resulting from their developmental asynchrony. We investigated patterns of ontogenetic selection acting on hatchery produced salmon fry by experimentally manipulating fry development stage at stocking. Contrary to simple predictions, we found evidence for strong stabilizing selection on the ontogeny of unfed hatchery fry, with weaker evidence for positive directional selection on the ontogeny of fed fry. These selection patterns suggest a seasonally independent tradeoff between abiotic or biotic selection favoring advanced development and physiological selection linked to risk of starvation in unfed fry. We show, through a heuristic exercise, how such selection on ontogeny may exacerbate problems in restoration efforts by impairing fry productivity and reducing effective population sizes by 13–81%.

Survival and life history characteristics among wild and hatchery coho salmon (Oncorhynchus kisutch) returns: how do unfed fry differ from smolt releases?

Survival and life history characteristics were evaluated for a coho salmon ( Oncorhynchus kisutch ) integrated hatchery program using two stocking strategies. Fish were released as unfed fry or smolts and returned as adults, and then molecular analysis was employed to pedigree the entire population. We showed that mean adult survival of individuals released as unfed fry was less than that of individuals released as smolts (0.03% vs. 2.39%). The relative reproductive success (RRS) of the fry release strategy to wild spawning was significantly greater for one of two cohorts, whereas the smolt release strategy to wild RRS was significantly greater for both cohorts. Fish released as smolts were significantly smaller upon returning as adults than either those released as unfed fry or wild returns. Mean run timing was also significantly biased towards an earlier run time for hatchery-released fish when compared with the wild component. The incidence of jacking (males maturing at age 2) was greater among fish stocked as smolts than for fish stocked as fry. Differences in survival, RRS, and life history appeared to be the result of hatchery practices and indicated that a fry stocking strategy produced fish more similar to the wild component of the population than to that of fish released as smolts.

Multiple marking of otoliths of brown trout,Salmo truttaL., with alizarin redS to compare efficiency of stocking of three early life stages

Abstract This study examined stocking with three early life stages of brown trout,Salmo truttaL., in the context of rehabilitating a native lineage. Experimental sections in five streams were stocked successively with three stages (I: unfed fry at the end of the reabsorption phase, II: fed fry measuring 2–3 cm and III: fed fry measuring 4–5 cm) derived from a hatchery stock bred from wild spawners. The three stages were distinguished by single or multiple fluoromarking of the otoliths with alizarin redS. The index of relative stocking efficiency was greater for stage II than for stage I in all sections and equivalent or greater than that for stage III. Stage II achieved significantly larger mean length and weight in autumn than stage III stockings.

Preliminary Observations on the Cost of Producing Fingerling Channel Catfish, Ictalurus punctatusStocked as Sac Fry or as Hatchery-Fed Swim-Up Fry

Some producers of channel catfish, Ictalurus punctatusfingerlings stock sac fry in nursery ponds as early as two days after hatching to reduce hatchery operating costs associated with the traditional practice of feeding swim-up fry for 7–10 days prior to stocking. It is not known if the reduced costs associated with the elimination of hatchery feeding of swim-up fry are countered by reduced production of fingerlings from ponds stocked with unfed sac fry. This study was conducted to determine if stocking catfish fry two days after hatch (unfed sac fry) or 10 days after hatch (hatchery-fed swim-up fry) had significant effects on the subsequent production of fingerlings and the profitability of a fingerling production operation under practical production conditions. In two consecutive years, catfish fry were stocked in 0.08-ha ponds in the spring of the year and harvested about six months later. Sac fry were stocked at a density (mean±SD of both years) of 24,953±2,876/ ha; swim-up fry at a density of 31,473±9,260/ha. Fry were fed a 45%-protein mash for several weeks after stocking and then a 38%-protein crumble for the remainder of the production trial each year. There were no statistically significant (P > 0.05) differences in yield (sac fry, 40±39 kg/pond; swim-up fry, 30±17 kg/pond), number harvested (sac fry, 2,521±2,720 fish/ha; swim-up fry, 1,988±3,059 fish/ha), or survival (sac fry, 10±11%; swim-up fry, 6±9%) of fingerling catfish stocked as either sac fry or swim-up fry. Total annual savings were estimated to be $17,636 (1% of total specified expenses) for a medium-sized hatchery that produced sac fry, compared with a hatchery that produced and fed swim-up fry. Fry survival was a critical factor influencing revenue. In this study, feeding catfish swim-up fry in the hatchery for seven days prior to stocking in ponds for grow-out to fingerling size provided no benefit, in terms of fish survival or the quantity of fingerlings produced, when compared with fingerling yields from ponds stocked with two-day old (unfed) sac fry. Thus, hatchery feeding of swim-up fry may be an uneconomical practice that might be effectively replaced by the stocking of sac fry within 48 hours of hatching. Additional research is needed to determine if the results obtained in this study can be expected to occur under a wider range of production conditions before recommendations on the stocking of catfish sac fry are developed.

Concentrations of erythromycin and azithromycin in mature Chinook salmon Oncorhynchus tshawytscha after intraperitoneal injection, and in their progeny

A single dose (40 mg kg(-1)) of erythromycin or azithromycin dihydrate was injected intraperitoneally into maturing female fall Chinook salmon 12 to 32 d before spawning to observe the distribution, retention and clearance of the drugs in plasma, kidney, coelomic fluid and egg vitellin, and their persistence in alevins derived from these fish. Salmon administered prophylactic dosages of erythromycin as subadults were also included to investigate potential interactive effects of oral and injected treatments on reproductive performance and antibiotic clearance. Erythromycin was rapidly cleared from plasma and coelomic fluid, but was detected in the kidney (3.52 to 12.40 microg g(-1)) and egg vitellin (5.32 to 8.87 microg ml(-1)) of all fish at spawning. High, stable concentrations of azithromycin were detected in plasma (14.66 to 20.33 microg ml(-1)), kidney (43.16 to 59.96 microg g(-1)), coelomic fluid (2.52 to 5.50 microg ml(-1)) and egg vitellin (12.65 to 23.51 microg ml(-1)). Oral administration of erythromycin to subadult salmon did not significantly affect tissue concentrations of either erythromycin or azithromycin administered by prespawning injection. Reductions in the percentage of eggs that yielded live embryos at the eyed stage of development occurred among eggs derived from females that had received orally administered erythromycin as subadults. Erythromycin was not detected in unfed fry derived from adults injected with the drug prespawning, but azithromycin was present for more than 2 mo after the onset of exogenous feeding.

Testing predictions of the critical period for survival concept using experiments with stocked Atlantic salmon

Two separate field experiments were performed in the U.S.A. and Norway with stocked Atlantic salmonSalmo salar. In the Norwegian experiment, the offspring of early‐spawning fish which had larger eggs and emerged a few days before offspring of later spawning fish had consistently higher survival rates. In the U.S.A. experiment, stream sections with higher proportions of favourable foraging locations during the critical period (the transition from dependence on maternally‐derived yolk reserves to independent feeding) had lower loss rates of fish stocked as unfed fry. These results provide support for the critical period concept (CPC) in Atlantic salmon, underscores the utility of a manipulative approach to achieve further advances in knowledge of Atlantic salmon ecology and provide additional guidance to management and restoration. A mechanistic, conceptual model for density dependence is presented to identify important knowledge gaps that remain to further evaluate the importance of the CPC for Atlantic salmon population regulation.

Recovery and re‐establishment of Atlantic salmon, Salmo salar, in limed Norwegian rivers

AbstractA total of 21 acidified Norwegian rivers are now being limed to re‐establish or restore Atlantic salmon, Salmo salar L., stocks. Natural reproduction of Atlantic salmon was evident 1 year after the first year of liming in all rivers that had lost their native stocks (n = 9) except for one river. The density of fry (age 0+) developed significantly more rapidly in rivers that supported remnant stocks than in rivers that had lost their stocks, based on data 5 years after treatment. Nine of the study rivers were supplied with hatchery‐reared salmon, mainly unfed fry. Of the rivers with lost stocks, those which were supplied with fish had significantly higher densities than those that were not enhanced. On the other hand, rivers with remnant stocks that were supplied with fish had significantly lower densities of salmon fry than those that did not undergo such mitigation measures. In 2001, all limed rivers yielded 41.9 t of salmon.

Starvation Resistance in Lake Trout Fry

Newly hatched fry were acclimated to 7 or 12°C and either fed daily (controls) or denied food for varying lengths of time and then fed daily until the end of the study (day 91 at 7°C and day 43 at 12°C). Growth was reduced by delays in the onset of feeding of 27 or more days at 7°C and 7 or more days at 12°C. Mortality of fry unfed for more than 34 days at 7°C, or more than 21 days at 12°C, was higher than among controls. Daily mortality increased with the length of the food deprivation period and did not cease immediately when food was made available, but reached zero by the end of the study. Mortality among unfed fry reached 50% in about 59 days at 7°C and 32 days at 12°C. Study results permitted calculation of the “point-of-no-return” (PNR) mortality, which included the mortality that occurred during the period of food deprivation, and also the delayed component of mortality that was directly attributable to starvation and that occurred after food was made available. The PNR for 50% mortality for food-deprived fry occurred after 52 days at 7°C and 24 days at 12°C. Thus, both measures of mortality indicate that lake trout fry would be highly resistant to death by starvation in the thermal habitat they would be expected to occupy in the Great Lakes. We conclude that a more likely adverse effect of reduced food availability would result from a reduction in growth rate that extends the length of time fry remain small and vulnerable to predation by adult alewives and other non-native fishes with which they associate.

Survival and Growth of Unfed and Fed Atlantic Salmon Fry Stocked in a Vermont Tributary of the Connecticut River

Abstract We studied Atlantic salmon Salmo salar to determine the effect of fry feeding stage on survival and growth to late summer age-0 parr in a Vermont tributary of the Connecticut River. In 1989, the mean mortality rates of unfed fry stocked on 19 May and 31 May were similar to the rate for fed fry stocked on 1 June (range: 0.018–0.031). By contrast, in 1990, mortality of fed fry stocked on 13 June (0.015) was significantly lower than that of unfed fry stocked on 11 May (0.022). The greatest late summer mean density of age-0 parr over the two study years (10 fish/100 m2) was produced by stocking large fed fry in mid-June. By late summer, all fry achieved a total length of 65–80 mm. Stocking large fed fry late in the season may be a means of increasing Atlantic salmon production in streams where unfed fry survival has been poor. However, given the variability of fry mortality rates among treatments, further evaluation is warranted before introductions of fed fry are widely considered, particularly to d...

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.

Technical Notes: Survival of Golden Shiner Fry Fed a Microparticulate Diet

Abstract Growth and survival were compared for fry of' golden shiner (Notemigonus crysoleucas) reared in indoor tanks and fed different sizes of a commercially available dry fry feed. The 3–4-d-old fry were stocked in 80-L tanks at 50 fry/L and were fed to excess 12 times daily for 7 d with Fry Feed Kyowa B-250 (particle size < 250 μm), B-400 (250–400 μm), or B-700 (400–700 um). For fry fed FFKB-250, FFKB-400, and FFKB-700, survival averaged 46.4%, 7.0%, and 1.4% and final total lengths averaged 5.4, 5.1, and 4.7 mm, respectively. Survival was significantly (P < 0.05) higher for fry fed the FFKB-250 diet. Unfed fry did not survive beyond 7 d posthatch.

Survival, Growth, and Smolt Production of Atlantic Salmon Stocked as Fry in a Southern New England Stream

Abstract The performance of Atlantic salmon Salmo salar stocked as fry was assessed in a third-order stream of the lower Connecticut River system. Stocking densities of 100–150 unfed fry per 100 m2 of stream area were tested for their ability to maximize smolt production. Because the Connecticut River no longer had a natural population of Atlantic salmon, fry originating from the Penobscot River of Maine were stocked in 1982, 1984, and 1985. In 1983, the Penobscot strain was unavailable and fry originating from Iceland were used instead. Although stocking conditions were not always favorable, an average of 27% of Penobscot fry survived to the fall age-0 pan stage. In contrast, only 2% of Icelandic fry survived to this stage, The low survival of Icelandic fry may have been due to their smaller total lengths and to intraspecific competition from an abundant population of yearlings that had been stocked in 1982. However, these factors would not have influenced summer-to-fall survival of yearlings, which was ...

Habitat Availability and Carrying Capacity in the French Part of the Rhine for Atlantic Salmon (Salmo Salar L.)

A survey of potential spawning grounds and rearing habitats for Atlantic salmon was conducted in the French part of the Rhine Basin in Alsace, using a macro-habitat description method. Aerial photography was used for the Rhine whereas tributaries were described from a canoe. 113 ha of rearing habitat and 6 ha of spawning grounds were recorded, of which about half were in the I11 catchment and half in the Old Rhine between France and Germany. Their carrying capacity was evaluated on the basis of stocking tests. Parr densities at the end of the summer ranged from 0 to 26 0+ parr per 100 m2 of suitable habitat with unfed fry and from 5 to 70 with feeding fry (4-5 cm). The overall carrying capacity of the French part of the Rhine for Atlantic salmon is estimated at 344 100 yearling parr for the whole area. The carrying capacity would enable a production of 56 000 to 112 000 smolts, of which 70%are one year-old and 30% two-year-olds. Mortality through hydroelectric turbines during downstream migration was estimated at 20% of the smolt run. On a basis of a 2% return rate at the eventual stage of the reintroduction period, 900 to 1700 adults would return each year to the area. Recommendations are made to protect and restore vanishing running waters needed for salmonids.

The ontogeny of drinking in the rainbow trout, Oncorhynchus mykiss (Walbaum)

Drinking was measured by the rate of uptake of tritiated dextran in fresh water by the alevins and fry of rainbow trout at various stages of development during a 40‐day post‐hatch period. Drinking increased almost S‐fold during the initial 16 day yolk‐sac stage. Drinking rate increased most between 16 and 23 days, the transitional period between yolk‐sac absorption and first feeding. The maximum weight‐specific drinkingrateof 3.24μlg−1 h−1 recorded for 40‐day‐old fry was higher than previously recorded for adults. Abrupt transfer from an adaptation temperature of 10 to 19° C increased drinking significantly (Q10= 1.2), but sudden transfer to 1 1‰ salinity sea water caused a substantial fall in drinking rate in 23‐day fry. A 24‐h period of adaptation to 1 1‰ and 15‰ salinity restored drinking to a rate similar to that in fresh water. The water drunk by 31‐day fry fed to satiation was initially higher than by unfed fry, but drinking rates subsequently fell below the control level. The results are discussed in terms of osmoregulation and the uptake of dissolved or suspended substances by the intestinal tract for the purpose of immunization.

The critical‐period concept for juvenile survival and its relevance for population regulation in young sea trout, Salmo trutta

An example of density‐dependent regulation is provided by a long‐term investigation (1966‐present) of a population of migratory trout (estuarine and sea trout), Salmo trutta L., in a Lake District stream. Evidence for the concept of a critical period for the survival of young fish is briefly reviewed and found to be rather equivocal. The concept is, however, relevant to the trout population. Loss rates were high before but low after a critical survival time (tc days after fry emergence) that varied between year‐classes (range 33‐70 days) and was inversely density‐dependent on egg density. Survivor density and loss rates were strongly density‐dependent on egg density before tc, but proportionate survival with stable loss‐rates occurred after tc. Some trout established feeding territories soon after emergence and the number of fish without territories decreased from a high initial value to a negligible value at tc. Fish size at tc was not constant but increased as tc increased. The range of tc for the different year‐classes was similar to that for survival times of unfed fry in the laboratory. A new stock‐recruitment model, incorporating tc, has been developed for the trout population and shown to be related to the model (Ricker curve) used in the long‐term study. The critical time can also be regarded as the critical age for survival in young trout; this concept may be relevant to other fish species.

Influence of egg size on the growth, onset of feeding, point-of-no-return, and survival of unfed Oreochromis mossambicus fry

The variation in egg size within and between egg clutches of O. mossambicus, and the subsequent influence of mean egg size on growth, feeding incidence and survival of unfed fry were investigated. The individual egg sizes within 90% of the egg clutches examined were normally distributed and the coefficient of variation of egg size within clutches ranged from 7.4% to 15.4%. Fry emerging from the small, medium and large egg size groups reached their maximum length and weight at 9, 9 and 12 days after hatching, respectively. Maximum attainable fry length and weight were significantly correlated with egg size ( r = 0.885 and 0.947, respectively, with P < 0.01). Egg size had little influence on the onset of feeding. Fry were capable of exogenous feeding within 6 to 7 days of hatching. Fry originating from small and medium egg size classes reached the point-of-no-return at 15–16 days after hatching compared to 21 days for fry from the large egg size class. The mean survival time (ST 50) of fry on their yolk reserves was significantly correlated ( r = 0.923; P < 0.01) with their original mean egg weight and ranged from 9.5 days for fry hatching from 0.91-mg eggs to 21 days for fry from 1.93-mg eggs.

Factors affecting the survival of dace, Leuciscus leuciscus (L.), in the early post‐hatching period

Young dace fry were stocked into nylon mesh cages at densities ranging from 0·044 to 7·230 1‐1, and the cages anchored in a backwater area where the fry gathered naturally. The fry began feeding on small organisms drifting into the cages 2‐4 days after hatching. The growth rate of the fry was inversely proportional, and the death rate directly proportional, to initial density. Soon after the exhaustion of endogenous food reserves (as determined from unfed fry), there was a period of massive mortality at the highest initial densities, probably due to starvation. After 20 weeks, the cages stocked at the two highest initial densities contained the lowest biomass of fry. Transfer of fry to cages with a larger mesh size produced increased growth and 46% survival over 20 weeks at the lowest initial density. These fry reached an overwintering length of 35·5 mm compared with 48·0 mm for naturally occurring fry.