Fitness component assessments of wild-type and growth hormone transgenic coho salmon reared in seawater mesocosms

Abstract

Growth hormone (GH) transgenic fish have been proposed for use in aquaculture to enhance production efficiency. As part of a risk analysis for use of such fish, the influence of GH transgenesis on the potential to persist and succeed in natural ecosystems is being examined in confined laboratory conditions. GH transgenesis can greatly accelerate growth and, in culture conditions, is associated with secondary effects such as poor swimming capacity and spawning success. However, standard culture has also been shown to negatively affect fitness components of wild-type fish, raising the question of whether culture conditions influence fitness components of transgenic fish in a similar way. To examine factors influencing the phenotype of marine-stage GH transgenic salmon (T), and to determine if genotype-by-environment interactions exist at this life stage, we grew T and wild-type (NT) coho salmon (Oncorhynchus kisutch) over six cohort years in 350,000L seawater tanks (termed mesocosms) designed to minimize effects of standard culture conditions. Mesocosm rearing partially facilitated development of normal size and morphology of NT fish relative to nature-reared counterparts, but altered overall body shape, indicating mesocosm conditions do not fully mimic natural environmental effects on coho salmon phenotype. T fish reared in mesocosms had larger mass at maturity than mesocosm- or nature-reared NT fish, indicating GH transgenesis can alter maximum obtainable mass in salmon. Unlike NT, T fish obtained maximum size at maturity across environments, suggesting marine environmental conditions may affect T growth less than NT growth. Screening parents for a common disease agent (Renibacterium salmoninarum) improved seawater survival, and T fish had lower survival than NT fish when from unscreened parents and inconsistent relative survival when from screened parents, indicating GH transgenesis may constitute an advantage or disadvantage in terms of survival. Transgenic salmon had lower swimming capacity and aerobic scope, but similar routine metabolic rate and thermal tolerance, demonstrating transgenesis can have different influences depending on what phenotype is examined. Using an alternate strain of T fish in phenotypic comparisons did not greatly influence most fitness components, although had a strong effect on female fecundity. The inconsistent influence of GH transgenesis on different fitness components, and existence of genotype-by-environment interactions during the marine life stage, complicates extrapolation of laboratory data for transgenic fish to natural environments. However, current and previous data do not provide evidence that overall increased performance of GH transgenic salmon over wild-type fish would arise in the marine environment. Statement of relevanceRearing in seawater mesocosms demonstrate that growth hormone transgenesis has inconsistent effects on marine fitness components in coho salmon.