Hatchery Stocks Research Articles

Evaluating protection against Loma salmonae generated from primary exposure of rainbow trout, Oncorhynchus mykiss (Walbaum), outside of the xenoma‐expression temperature boundaries

A series of challenge and re‐challenge studies was conducted in which juvenile rainbow trout were exposed to the pathogen Loma salmonae, a microsporidian which typically causes xenoma formation during sporogony and inflammation in the gills as the xenomas undergo dissolution. The specific goal was to determine if a primary exposure, conducted at a water temperature outside of the range which permits the parasite to undergo sporogony and form branchial xenomas, would stimulate a protective response in the fish to a later challenge conducted under temperature conditions optimal for the parasite. Primary challenge of fish to L. salmonae at 7 °C or 21 °C blocked or limited xenoma formation, as discussed in a previous study. However, these fish had a relative percentage protection (RPP) against a second optimized exposure which matched, or was not significantly less than, the degree of protection (100%) that developed in other groups of fish that received a primary exposure throughout the range of water temperatures which permits xenoma formation. When the primary exposure was conducted at 5 °C, the RPP against the second exposure was adversely affected and declined to 61%. These findings have application to the control of L. salmonae within aquaculture, in that it may be possible to expose hatchery stocks of susceptible salmonid species to spores of L. salmonae when hatchery water temperature is at 7 °C. At this temperature, the risks of disease stemming from this primary exposure appear minimal, since xenomas fail to form. However, the degree of protection appears promising, and may be sufficient to protect fish from spore exposure occurring at netpen marine sites where the parasite may be endemic.

Inheritance of a chromosomal polymorphism in odd-year pink salmon from southeastern Alaska

In previous work we found a high frequency of heterozygotes for a fission translocation involving the seventh chromosome pair in odd-year populations of pink salmon (Oncorhynchus gorbuscha) sampled from Washington State to south central Alaska. The populations from southeastern Alaska and northern British Columbia had high frequencies of heterozygotes for a second rearrangement of this same chromosome pair. In these fish one fission product, the larger acrocentric chromosome bearing the nucleolar organizer region (NOR), has undergone an inversion to produce a submetacentric chromosome. In this paper, we present inheritance data on pink salmon from the Gastineau hatchery stock in Juneau, Alaska, where individuals with the two rearrangements are found. Although most of the fish were either homozygous for the normal cytotype or heterozygous for the inversion cytotype, a few individuals heterozygous for the fission cytotype were found. Ten males and ten females were karyotyped, and crosses were set up in all combinations. Individuals with both rearrangements were found in crosses between the two types of heterozygotes, and the ratios of cytotypes in the progeny did not deviate significantly from the expected values. No significant difference in viability of offspring from crosses between individuals with different cytotypes was found up to the age of hatching.Key words: salmon, chromosomal polymorphism, translocation, inversion, cytotype.

Phylogeographic lineages and differentiation pattern of Atlantic salmon (Salmo salar) in the Baltic Sea with management implications

The genetic structure and isolation pattern of the Atlantic salmon (Salmo salar) throughout its range in the Baltic Sea were examined as a starting point for a conservation strategy for the species in this area. The allozyme variation in seven polymorphic loci was studied in 5125 salmon from 24 rivers in four countries. A clear dichotomy was observed between stock groups from southeastern (Russia, Estonia, Latvia, southern Sweden) and northwestern (northern Finland, northern Sweden) drainage regions, corresponding to the postglacial colonisation of the Baltic Sea by two phylogeographic lineages, one from the east (the Ice Lake lineage) and one from the west (the Atlantic lineage). The geographical and genetic distances between stocks fit the one-dimensional "isolation-by-distance" model (p < 0.001). The estimated gene flow ranged from 0 to10 migrants per generation. The total diversity of hatchery stocks was 72% of that of the wild stocks. Genetically similar stock groups, phylogeographic lineages, and drainage regions are recommended for use as genetic management units in addition to stock level.

Erosion of the native genetic resources of brown trout in Spain

Abstract– We analyzed the introduction of hatchery‐reared trout in the Riutort Creek, a small stream in the eastern Spanish Pyrennees. We used gene correlation matrices between individuals to analyze the fish coancestry in the Riutort Creek samples and in the hatchery stock. Hatchery fish disturbed the single ancestry in the native population of the creek, and were clearly detected with principal coordinate analysis of the gene correlation matrix. The amount of introgression produced by successful introductions was estimated from the principal coordinate analysis projections of the matrix of FST values between the putative native Riutort Creek population, the hatchery stock and the introgressed population. In only two years the amount of introgression rose to 10%, indicating that 5% of the native ancestry is lost each year as a result of the stocking program. Based on these results, we review the present understandings on the genetic impact of hatchery fish on indigenous Spanish brown trout populations. The stocking of these populations involves a non‐native broodstock widespread through the Spanish hatcheries, but successful stockings appear to be limited to wild populations subjected to occasional releases in protected or unfished areas. Surprisingly, extensive stocking in fished areas result in a more limited genetic impact on the recipient native population.

Genetic characterization of Portuguese brown trout (Salmo trutta L.) and comparison with other European populations

Abstract– Allozyme and other protein loci were examined to study the genetic structure of Portuguese brown trout (Salmo trutta) populations. A total of 247 individuals from three tributaries of the Lima hydrological basin and a hatchery, all located in northern Portugal, were analyzed. Four of 22 protein coding loci were found to be polymorphic: CK‐A1*, GPI‐A2*, MPI‐2* and TF*. A new allelc at the latter locus was found in Atlantic populations. The data obtained for Portuguese brown trout were compared with published data for 14 European populations and three hatchery stocks. Six polymorphic loci (CK‐A1*, GPI‐A2*, GPI‐B2*, LDH‐C*, ME* and MPI‐2*) were used in a cluster analysis. This showed the similarity of Portuguese natural populations and northern Iberian populations and that Portuguese hatchery fish have an autochthonous origin, distinct from that of other Atlantic hatchery stocks.

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

– 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 individuals 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.

Microsatellite polymorphism and genetic impact of restocking in mediterranean brown trout (Salmo trutta L.)

The genetic impact of restocking Mediterranean brown trout populations with hatchery stocks was investigated in the Orb River drainage (France), using genetic data from three microsatellite loci. We sampled two wild populations, the main river which is restocked each year and one of its tributaries which has not been restocked for 6 years. Each sample was divided into two age groups (juveniles/adults). Introgression of each native population by hatchery stocks was previously estimated using allele frequencies from two diagnostic protein-coding loci and one mtDNA haplotype. The genetic structure and allelic frequency at three microsatellite loci in native populations were compared with two hatchery samples belonging to stocks usually used for restocking this drainage. High levels of polymorphism (23-27 alleles per locus) were detected for two loci, whereas the third was less polymorphic. Polymorphism was significantly higher in the restocked population than in the now undisturbed population. Significant differences between age groups were observed in the main river, but not in its tributary. The introgression estimates using microsatellites were compared to those obtained from proteins and mtDNA. The different possible origins of alleles common to hatcheries and wild populations (homoplasy, ancestral polymorphism or introgression) are discussed.

Restriction fragment length polymorphism at the growth hormone 1 gene in Atlantic salmon ( Salmo salar L.) and its association with weight among the offspring of a hatchery stock

Variation was studied within an 1825 bp fragment of the Atlantic salmon growth hormone 1 ( GH1) gene, encompassing the sequence from the first to the fourth exon. Two novel polymorphisms were detected in a hatchery strain of landlocked salmon population from the Lake Vänern, Sweden (spawns in the River Gullspång) after PCR amplification and subsequent digestion of the GH1 fragment with TaqI restriction enzyme: restriction site polymorphism within a 562 bp fragment and length polymorphism of a 187 bp fragment. Altogether six different banding patterns were observed that arose from random association of three haplotypes. In order to study possible association of the detected variation with the weight of one-year-old fish, progeny of the hatchery strain was graded into three size groups. Significant heterogeneity of the GH1 haplotype and genotype frequencies among the size groups was detected ( P<0.05). However, the hypothesis that the samples with different genotypes or haplotypes have non-identical medians of weight distribution was rejected at the studied sample size ( P>0.05).

Phylogeographic lineages and differentiation pattern of Atlantic salmon (&lt;i&gt;Salmo salar&lt;/i&gt;) in the Baltic Sea with management implications

The genetic structure and isolation pattern of the Atlantic salmon (Salmo salar) throughout its range in the Baltic Sea were examined as a starting point for a conservation strategy for the species in this area. The allozyme variation in seven polymorphic loci was studied in 5125 salmon from 24 rivers in four countries. A clear dichotomy was observed between stock groups from southeastern (Russia, Estonia, Latvia, southern Sweden) and northwestern (northern Finland, northern Sweden) drainage regions, corresponding to the postglacial colonisation of the Baltic Sea by two phylogeographic lineages, one from the east (the Ice Lake lineage) and one from the west (the Atlantic lineage). The geographical and genetic distances between stocks fit the one-dimensional "isolation-by-distance" model (p < 0.001). The estimated gene flow ranged from 0 to10 migrants per generation. The total diversity of hatchery stocks was 72% of that of the wild stocks. Genetically similar stock groups, phylogeographic lineages, and drainage regions are recommended for use as genetic management units in addition to stock level.

The Potential for Restoration of Acid‐Damaged Lake Trout Lakes

This review of long‐term monitoring and experimental manipulation studies from Ontario, Canada, offers encouraging evidence that lake trout (Salvelinus namaycush) populations can be restored to acidified lakes once the problem of acid deposition is solved in North America. Predicting the rate of chemical and biological recovery remains difficult, because there are several limnological attributes (dissolved organic carbon, flushing rate) and biological attributes (acid sensitivity, species longevity, fish community composition) of lake trout ecosystems that can either enhance or delay the recovery process. Some options for managing recovering lakes are also reviewed, including increased pollution controls, liming, hatchery stocking, and harvest controls.

Use of Random Amplified Polymorphic DNA (RAPD) for Identification of Largemouth Bass Subspecies and Their Intergrades

Random amplified polymorphic DNA (RAPD) analysis was investigated as an alternative to conventional electrophoresis for subspecies identification of largemouth bass Micropterus salmoides. Seventeen primers were analyzed by RAPD for their ability to identify polymorphisms, and the three primers that gave the most polymorphisms were used for the study. Fifteen markers were identified and were shown to indicate fixed differences between the two subspecies. Intergrades of unknown origin were distinguishable from pure Florida and pure northern wild and hatchery stocks, as well as first generation intergrades (F1s). The RAPD analysis was more sensitive than traditional histochemical agarose gel electrophoresis for identification of largemouth bass subspecies.

Modeling the Effects of Poststocking Survival Rates on the Success of Stocking Hatchery Atlantic Salmon in a New Brunswick River

The effect of poststocking survival rate on the success of a hatchery stocking program to enhance Atlantic salmon Salmo salar was modeled with empirical data from the Nepisiguit River, New Brunswick, Canada. Removal of adults from the wild population for use as hatchery broodstock was beneficial to population growth if the survival rate of their hatchery-reared progeny was 10% or more of that of wild-reared juveniles in the first year following stocking and equivalent to the survival of wild-reared juveniles and adults thereafter. Returns of marked adult fish to a counting fence were consistent with average poststocking survival rates (relative to wild-reared fish) of 5–20%, so it appears the hatchery program was probably successful in enhancing returns of adult Atlantic salmon to the river.

Survival and Growth of Two Stocks of Presmolt Chinook Salmon Held Overwinter in Marine Net-Pens with an Artificial Freshwater Lens

Abstract Two hatchery stocks of juvenile spring chinook salmon Oncorhynchus tshawytscha originating from two southeast Alaska rivers were reared in freshwater to an average size of 8–10 g and placed in marine net-pens with an artificial freshwater lens system (AFLS) at four entry times from mid-September to early November 1987. Overwinter survival to May 1988 averaged 83.6% for Unuk River stock and 76.0% for Chickamin River stock and did not differ significantly in the AFLS among the four entry dates. Survival over 24 h differed significantly when entry was directly into 30‰ seawater. The 24-h plasma sodium levels in the juveniles challenged to either full-strength seawater or marine net-pens with an AFLS were not useful predictors of overwinter survival. Over winter, both stocks grew significantly better in the AFLS than in freshwater. The AFLS appears to be a cost-effective means of substantially increasing smolt production while minimizing freshwater use.

Strontium:calcium ratios in Atlantic salmon (Salmo salar) otoliths and observations on growth and maturation

In this paper, we report on two data sets that have relevance to contemporary ideas on maturation in Atlantic salmon (Salmo salar): (i) an analysis of maturity rate of Atlantic salmon captured in the southern Labrador Sea and (ii) a study of otolith strontium:calcium ratios for maturing and immature Atlantic salmon. A discrimination function based on gonadosomatic indices was developed to classify maturation state of Atlantic salmon caught in Newfoundland and Labrador fisheries during the period 1985-1988. Atlantic salmon believed to be on feeding migrations were found to be in advanced states of sexual development. In an attempt to clarify the meaning of these data, chronological transects of Sr:Ca ratios from the otoliths of maturing and immature one-seawinter fish were collected. Sr:Ca ratios deposited during freshwater residency varied by stock and appeared to reflect the environmental availability of Sr. Sr:Ca ratios deposited during marine residency appeared to reflect somatic growth and sexual development. We detected no differences in the postsmolt Sr:Ca ratios for mature and immature Atlantic salmon from a hatchery stock originating in North America, suggesting that for this stock, little differentiation occurs between the maturity components. Mechanisms by which environment may contribute to the variation in maturation rate of North American Atlantic salmon are discussed.

Length variation in mtDNA control region in hatchery stocks of European sea bass subjected to acclimation experiments

Length polymorphism of the mtDNA control region was analysed in samples from the sea bass Dicentrarchus labrax before and after acclimation to freshwater. Acclimation trials were repeated twice for two samples originating from the same broodstock. DNA amplification of 221 individuals made it possible to detect 40 different D-loop length variants and a mean level of gene diversity (/c!) of 0.850. Out of 52 scored distinct genotypes, 18 were homoplasmic and the remaining ones were heteroplasmic for up to four variants. Shifts in frequencies between starting and acclimated samples in the same direction of the same genotypes in both years were not observed. Patterns of mtDNA control region variation were compared to previous allozymic and RAPD studies carried out on the same samples. While variation found in the allozyme alleles and the RAPD markers in replicate experiments revealed differential survival of the genotypes, stochastic processes, such as genetic drift, explained the observed variation of mtDNA control region. Very high levels of genotype diversity were observed within each sample, ranging from 0.77 to 0.97. This high diversity associated with the maternal inheritance of mtDNA makes this molecular marker especially suitable for studies in aquaculture genetics, when the allozyme studies fail to reveal genetic variation or when the identification of progeny based on the mother's contribution is relevant. © Inra/Elsevier, Paris

Length variation in mtDNA control region in hatchery stocks of European sea bass subjected to acclimation experiments

Length variation in mtDNA control region in hatchery stocks of European sea bass subjected to acclimation experiments

The contribution of Atlantic salmon (Salmo salar L.) enhancement to a sustainable resource

Enhancement methods have been applied for more than a century throughout the natural range of the Atlantic salmon (Salmo salar L.). Hatcheries, the cornerstone of enhancement programmes, are used to: facilitate colonization of new habitats; restore or rehabilitate stocks to once productive habitats; supplement wild stock production; compensate for major environmental disturbances or problems such as hydroelectric development and acid rain; support fisheries entirely dependent upon hatchery stocking; and foster research and technology development. The benefits from enhancement programmes include: contributing to fisheries and wild stock conservation; increased awareness of the resource and natural environment; technology support for the aquaculture industry; and increased knowledge of salmon biology. The risks from enhancement include: reduced genetic diversity and population fitness; adverse ecological effects; and further degradation and loss of wild stocks. Enhancement is one of a series of management measures that requires careful planning and should be fully integrated within management programmes for the stocks, the resource and its ecosystem. This paper reviews the application of enhancement technology in management programmes for Atlantic salmon in North America and Europe with emphasis on the former. Emphasis is placed on the use of hatcheries because of their prominence as an enhancement tool.

The advantage of using smolt age with allozymes for assessing wild stock contributions to Atlantic salmon catches in the Baltic Sea

Information about the occurrence and proportions of endangered wild Atlantic salmon stocks in Baltic Sea catches is invaluable to the fishery managers responsible for sustaining these populations. The usefulness of stock mixture analysis (SMA) from characters of sampled fish was evaluated by applying the method in an estimation of actual and simulated catch compositions. Samples for seven variable genetic loci, expressed by allozymes, and smolt age from 17 stocks from Finland and Sweden which are potential contributors to the fishery were used with similar samples collected in 1993 from catches in a Finnish trapnet fishery along the east coast of the Bothnian Sea. Identified by their character similarities, three stock management units and their estimated catch contributions were: resident Neva stock (29%), wild baseline stocks (28%), and migratory hatchery stocks (43%). The contributions of the units varied during the fishing season. With allozyme data alone, the management units were not so distinctive. Nevertheless, three major wild stocks (Tornionjoki, Kalixalven, and Simojoki), which accounted for 68% of the total wild smolt production of the area, were similar in their allozymes and distinctive from the other stocks. The increase in reliability of wild stock composition estimates when smolt age was added to the allozyme loci was evaluated by simulation. Smolt age improved the precision of composition estimates for both the combined wild baseline stocks and their aforementioned subset comprising three major stocks; it controlled bias better for the combined wild baseline stocks than their subset.

Localized Genetic Effects of a Long-Term Hatchery Stocking Program on Resident Rainbow Trout in the Metolius River, Oregon

Abstract Hatchery rainbow trout Oncorhynchus mykiss have been stocked in the Metolius River in central Oregon since 1938, and legal-sized (≥160 g) yearling trout were stocked annually from 1947 until 1995. In 1996, management objectives shifted to emphasize wild trout, and hatchery stocking ceased. We examined allozyme and mitochondrial DNA (mtDNA) variation among three naturally occurring populations of rainbow trout in the Metolius River to investigate possible hybridization with hatchery-produced rainbow trout. We also examined two commonly used hatchery strains of rainbow trout, one of which has supplied nearly all of the catchable hatchery trout in the Metolius. Both allozyme and mtDNA data showed the two hatchery samples to have genetic characteristics typical of hatchery populations derived from coastal rainbow trout O. mykiss irideus. Rainbow trout sampled from the lower Metolius River, approximately 30 km downstream of the headwaters, had allozyme and mtDNA characteristics typical of interior rai...

Response of Endangered Desert Fish Populations to a Constructed Refuge

AbstractThe U.S. Bureau of Reclamation created a shallow, 110‐m channel to provide habitat for two endangered fishes, Cyprinodon elegans (Comanche Springs pupfish) and Gambusia nobilis (Pecos gambusia), at the site of the fishes' former natural habitat. The ciénega (marsh) associated with Phantom Lake Spring in Jeff Davis County, Texas, was destroyed by the creation of an irrigation canal system. In 1993, the endangered fishes were stocked into the refuge with individuals from the irrigation canals, and in the case of C. elegans, hatchery stocks. The condition of habitat, status of fish populations, and fish ecology within the refuge were then monitored for two years. The abundance and density of both species increased in accordance with aquatic plant development. Cyprinodon elegans abundance peaked after one year and stabilized at an average density of 14.7/m2 by the end of our study. Juvenile C. elegans were always rare, which may indicate that the population reached the refuge's carrying capacity and that recruitment is low. Gambusia nobilis was the most abundant fish in the refuge (average density 96/m2), used the entire refuge, and outcom‐peted nonindigenous G. geiseri. The two Gambusia species used similar habitats but showed almost no dietary overlap. High densities of aquatic plants reduced the amount of open water areas necessary for C. elegans. The refuge will sustain the two endangered fishes at this historic site of endemism while maintaining flow to the irrigation system; however, the refuge is not equivalent to a restored ciénega.