Triploid Coho Salmon Research Articles

Effect of triploidy on liver gene expression in coho salmon (Oncorhynchus kisutch) under different metabolic states

BackgroundTriploid coho salmon are excellent models for studying gene dosage and the effects of increased cell volume on gene expression. Triploids have an additional haploid genome in each cell and have fewer but larger cells than diploid coho salmon to accommodate the increased genome size. Studying gene expression in triploid coho salmon provides insight into how gene expression may have been affected after the salmonid-specific genome duplication which occurred some 90 MYA. Triploid coho salmon are sterile and consequently can live longer and grow larger than diploid congeners in many semelparous species (spawning only once) because they never reach maturity and post-spawning mortality is averted. Triploid fishes are also of interest to the commercial sector (larger fish are more valuable) and to fisheries management since sterile fish can potentially minimize negative impacts of escaped fish in the wild.ResultsThe vast majority of genes in liver tissue had similar expression levels between diploid and triploid coho salmon, indicating that the same amount of mRNA transcripts were being produced per gene copy (positive gene dosage effects) within a larger volume cell. Several genes related to nutrition and compensatory growth were differentially expressed between diploid and triploid salmon, indicating that some loci are sensitive to cell size and/or DNA content per cell. To examine how robust expression between ploidies is under different conditions, a genetic/metabolic modifier in the form of different doses of a growth hormone transgene was used to assess gene expression under conditions that the genome has not naturally experienced or adapted to. While many (up to 1400) genes were differentially expressed between non-transgenic and transgenic fish, relatively few genes were differentially expressed between diploids and triploids with similar doses of the transgene. These observations indicate that the small effect of ploidy on gene expression is robust to large changes in physiological state.ConclusionsThese findings are of interest from a gene regulatory perspective, but also valuable for understanding phenotypic effects in triploids, transgenics, and triploid transgenics that could affect their utility in culture conditions and their fitness and potential consequences of release into nature.

Growth and endocrine effect of growth hormone transgene dosage in diploid and triploid coho salmon

Growth-hormone transgene dosage, polyploidy, and parental effects on growth and endocrine responses have been assessed in coho salmon. Diploid fry with one or two transgene doses grew equally, whereas later-stage juvenile homozygotes grew faster than hemizygotes. In contrast, homozygotes and hemizygotes grew equally after smoltification, both in sea water and fresh water. Triploid transgenic salmon showed impaired growth which could not be fully overcome with additional transgene copies. Levels of muscle GH mRNA were elevated in two vs. one transgene dose diploids, but in triploids, a dosage effect was observed in muscle but not for animals carrying three transgene doses. IGF-I mRNA levels were elevated in transgenic vs. non-transgenic animals, but a dosage effect was not observed. Diploids and triploids with two transgenes had higher plasma GH levels than one-dose animals, but three-dose triploids showed no further elevation. Circulating IGF-I levels also showed a dosage effect in diploids, but not among any transgene doses in triploids. The present study reveals complex interactions among transgene dosage, maternal effects, developmental stage, and ploidy on growth and endocrine parameters in GH transgenic coho salmon. Specifically, GH transgenes do not always express nor have effects on growth that are directly correlated with the number of transgenes. Further, the reduced growth rate seen in triploid transgenic animals could not be fully overcome by increasing transgene dosage. The findings have relevance for understanding growth physiology, transgene function, and for environmental risk assessments that require understanding phenotypes of hemizygous vs. homozygous transgenic animals in populations.

Disease resistance, stress response and effects of triploidy in growth hormone transgenic coho salmon

Diploid and triploid coho salmon Oncorhynchus kisutch transgenic for growth hormone (GH) and control coho salmon were compared for differences in disease resistance and stress response. Resistance to the bacterial pathogen Vibrio anguillarum was not affected in transgenic fish relative to their non‐transgenic counterparts when they were infected at the fry stage, but was lower in transgenic fish when infected near smolting. Vaccination against vibriosis provided equal protection to both transgenic and non‐transgenic fish. Triploid fish showed a lower resistance to vibriosis than their diploid counterparts. Diploid transgenic fish and non‐transgenic fish appeared to show similar physiological and cellular stress responses to a heat shock. These studies provide information useful for both performance and ecological risk assessments of growth‐accelerated coho salmon.

Effect of triploidy on growth and survival of pre-smolt and post-smolt coho salmon ( Oncorhynchus kisutch)

Growth and survival was monitored in full-sib diploid and triploid coho salmon families held at elevated temperature and accelerated photoperiod to induce them to smolt as underyearlings. At tagging, the diploids were significantly heavier than the triploids. After tagging, the diploid and triploid fish were reared in individual family tanks for another month before being combined into pooled groups for acclimation to salt water and transfer to seawater net pens. Diploid and triploid pre-smolts grew at the same rate over this period of acclimation to sea water. By the time of transfer to seawater net pens, the diploids were still slightly larger than the triploids, although the difference was not significant. The triploid post-smolts grew as well as the diploids throughout the first summer of seawater rearing. As a result, there was no significant difference in weight between diploids and triploid post-smolts by the following October. The growth of triploids relative to diploids was not consistent among families, resulting in a significant interaction of family and ploidy for weight, growth rate and condition factor. It is concluded that when triploid coho salmon are reared in a favourable environment, their performance is comparable to that of diploids during the smolt and post-smolt stages.

Freshwater growth, smolting, and marine survival and growth of diploid and triploid coho salmon ( Oncorhynchus kisutch)

Variation in weight, growth, survival, and smolting was examined for nine fullsib families of diploid and triploid coho salmon ( Oncorhynchus kisutch) from the Quinsam River B.C. Diploids survived substantially better than triploids from fertilization to hatching (94% vs. 43%), from hatching to ponding (96% vs. 76%), during freshwater rearing (92% vs. 75%), and during marine rearing (81% vs. 60%). About 77% of the diploids marked with coded wire (CW) tags smelted, whereas only 63% of the corresponding triploids smoked. About 71% of the diploids marked with passive integrated transponder (PIT) as well as CW tags smolted, whereas only 39% of the triploids carrying both types of tags smolted. Diploids were 65% heavier than the triploids at smolting, and 70% heavier after two summers of marine rearing. Marine growth of diploids was significantly faster than that of the triploids during the spring and summer of the year of maturity. The biomass of the diploid cohort was over three times greater than that of the triploid cohort at the termination of the experiment. Ploidy by family interactions for the characters examined were greatest during freshwater and early marine rearing. Although poor triploid performance was observed in this experiment, relative productivity may be enhanced by rearing triploids in isolation from diploids, or by a judicious choice of the triploid strain.

Saltwater Exposure at Fertilization Induces Ploidy Alterations. Including Mosaicism, in Salmonid

We found that salt water induces ploidy alterations in salmonid embryos. Flow cytometry analysis revealed significantly higher frequencies of haploids, triploids, heteroploid mosaics, and aneuploids in rainbow trout (Oncorhynchus mykiss) embryos experimentally exposed to salt water from fertilization to the two- and eight-cell stages of development. Heteroploid mosaics have been reported in diploid and triploid salmonid hybrids, although none were observed in the triploid coho salmon or diploid and triploid coho salmon (O. kisutch) × chinook salmon (O. tshawytscha) hybrids we examined. No mosaics were observed in intertidally spawned pink salmon (O. gorbuscha) embryos. Salt water could induce ploidy alterations by causing chromosome segregation errors during meiosis, mitosis, or both. Heteroploid embryos appeared morphologically normal although they may possess physiological deficiencies not immediately apparent.

Triploid Coho Salmon Outperform Diploid and Triploid Hybrids Between Coho Salmon and Chinook Salmon During Their First Year

Sterile hybrid and triploid fish may provide hatchery programs with a tool to reduce the risk of genetic contamination of wild stocks, provided these fish have acceptable performance characteristics. We examined growth, survival, and deformities in diploid and triploid families of coho salmon (Oncorhynchus kisutch) and hybrids between coho salmon females × chinook salmon (O. tshawytscha) males. Data were collected from the half-sibling families through day 387. A reparameterized Gompertz growth model showed that conspecific coho salmon grew faster than hybrids, regardless of ploidy. No difference in growth rates was found between diploids and triploids. Abnormalities were significantly associated with the male parent but not with ploidy component, in contrast to previous observations of reduced deformity occurrence in triploid hybrids. Food conversion was better for conspecifics than hybrids during initial feeding, but not different during the second half of the experiment. No ploidy or cross × ploidy interaction effects on food conversion efficiency were observed. Finally, conspecifics had better posthatching survival than hybrids, regardless of ploidy. Of the treatments studied, conspecific triploid coho salmon may be the most viable alternative for sterile fish production: they performed as well as the conspecific diploids and better than either diploid or triploid hybrids.

Production of female triploid coho salmon(Oncorhynchus kisutch)by pressure shock and direct estrogen treatment

Resume The aquaculture production of all-female triploid (sterile) populations is recognized as being of potential advantage for many species of fish where sexual maturation is not desired. All-female triploids have been produced by inducing triploidy in eggs that had been fertilized with monosex female sperm. However, monosex stocks to produce this type of sperm are currently available only for a limited number of economically important species. To circumvent this problem, an alternative method would be the direct ferninization of tripoid embryos. In Pacific salmon, pressure shocks applied shortly after fertilization have consistently resulted in high yields of tripoids, and feminization by direct estrogen treatment has also been shown to be highly effective if applied shortly after hatching. In this study, coho salmon eggs were made triploid by a pressure shock of 633 kg/cm2 for 4 min, applied 20 min after fertilization and incubation at 10°C. Some of the resulting embryos were then feminized with estradiol-17P in single 2-hour immersion treatments at 400 ~rglliter, administered 1 and 8 days after hatching. Six months later, when the fish were juveniles, analysis of the DNA content of erythrocytes by fluw cytometry revealed a 100% induction of triploidy, while histological examination of the gonads showed 82 % fernales, which were completely devoid of oocyte development and thus genetically sterile. These manipulations reduced survival during early stages of development but survival became stable later. Together, these results suggest that the production of sterile fish by direct feminization of induced triploids could be of pariicular advantage for those species in which all-female stocks are yet not available or difficult to obtain.

Growth enhancement following dietary delivery of recombinant porcine somatotropin to diploid and triploid coho salmon (Oncorhynchus kisutch)

Diploid (2n) and triploid (3n) coho salmon were fed upon control (diet 1), recombinant porcine somatotropin (rpST)-supplemented (diet 2; 20 μg rpST/g body wt/day) or rpST/antacid/detergent-containing feed (diet 3; 20, 100 & 20 μg/g body wt/day respectively) for 16 wk. Fish were weighed and measured bimonthly and their relative performances assessed. By wk 4, 2n and 3n groups fed upon diet 2 were significantly heavier and longer than control 2n fish. At the termination of the trial, diet 3 fed animals were greater in weight than all other treatment groups. Diet 3 salmon also returned better feed conversion efficiencies than either diet 1 or 2 groups. RpST therapy induced a 28.7% and 60.2% increase in group wt for 3n diet 2/3 coho versus (-vs-) controls. Likewise, 2n rpST-treated fish increased wt -vs-2n control coho by 17% and 50% respectively over the same period. No differences were recorded between groups for body moisture, but diet 2, 3n and both diet 3 groups exhibited decreased condition factors when compared to control fish (p ≤ 0.05).

Promotion of growth in diploid and triploid coho salmon with parenteral delivery of a recombinant porcine somatotropin

The growth response of diploid (2n ) and thermally-induced triploid (3n ) coho salmon to injected recombinant porcine somatotropin was examined over a 10 week period. All treatments were under-taken using replicate groups of 25 animals per group. Control 2n and 3n replicate groups grew at identical rates throughout the period of study, although 3n fish exhibited lower condition factors. Recombinant poreine somatotropin treated 2n and 3n fish responded positively to therapy and, by week 4 of the trial, expressed significantly greater increases in both weight and length (p < 0.01) when compared to controls. At the end of the study period, soinatotropin treated animals had gained approximately twice the amount of weight of controls. Food conversion efficiencies were greater in treated salmon, regardless of ploidy state. This relationship also extended to weight and length specific growth rates. The economic benefits of commercial application of recombinant porcine somatotropin therapy to triploid Pacific salmon culture are discussed.

Estrogen-induced vitellogenin production by triploid coho salmon ( Oncorhynchus kisutch), and its effect on plasma and pituitary gonadotropin

Vitellogenin production was induced in immature diploid and triploid coho salmon by the weekly injection of 17β-estradiol at 1 mg/kg body wt. There was no significant difference between diploids and triploids for any of the results obtained, i.e., change in plasma vitellogenin and gonadotropin levels, hepatosomatic index, or pituitary gonadotropin content. Plasma vitellogenin levels were significantly higher in 17β-estradiol-treated fish than in sham-injected fish within a week of the first injection, and continued to rise with each subsequent injection. Plasma gonadotropin levels, on the other hand, were slightly (but significantly) depressed. The 17β-estradiol-treated fish had higher hepatosomatic indices and pituitary gonadotropin contents than sham-injected fish by 3 weeks after the first treatment. These data suggest that the occasional postmeiotic oocytes observed in triploids do not grow to full maturity due, in part, to an absent or diminished estrogen stimulus from the ovary on hepatic vitellogenin production.

Effects of Triploidy on the Swimming Performance of Coho Salmon (Oncorhynchus kisutch)

The swimming performance of triploid coho salmon (Oncorhynchus kisutch) was compared with diploid controls to assess the ability of these fish to survive if released into the wild. Triploid salmon had similar haematocrits to diploid salmon but they had lower total haemoglobin content in their blood. There was no difference in the maximum sustained swimming ability between triploid and diploid salmon.

Cell size in triploid salmon

AbstractThere is a uniform increase in nuclear and cell size of erythrocytes, leukocytes, brain cells, and retinal cells in triploid coho and Atlantic salmon. In spite of the potentially drastic effects of this on their physiology and behavior, triploid fish appear to function as successfully as normal fish under aquaculture conditions. Triploid fish are easily produced, reared, and identified and should make useful tools for basic and applied research.

Comparative growth and development of diploid and triploid coho salmon, Oncorhynchus kisutch

This paper compares growth and gonadal development of triploid and diploid coho salmon in three treatment groups. The comparisons were made in fresh and seawater from the time of smoltification at 18 months to the onset of sexual maturity at 30 months. No differences were detected in the ability of triploids to smoltify and to successfully adapt to seawater under normal conditions. Likewise, no differences were observed in growth parameters (length, body weight or condition factor). Gonadal development in both sexes was severely retarded in all triploid groups at 30 months of age. The average gonadosomatic index (GSI) of triploid males was 35.7% of diploids, but overall male gonadal development was not far enough advanced to determine if spermiation was altered in the triploids. Triploid females showed an almost complete blockage of gonadal development and oocyte maturation. The average GSI of triploid females was 11.8% that of diploid females. Vitellogenin was undetectable in triploid females, but was present in diploid females; a correlated reduction in the hepato-somatic index was observed in triploid relative to diploid females. However, we did not detect any significant differences between levels of estradiol in the plasma of triploids and diploids at this time.