The Role of Cortisol in Sub-Fertility of Farmed Female Rainbow Trout
The rainbow trout (Oncorhynchus mykiss) has been farmed for several hundred years and as such many production aspects are highly efficient using the current well-established practices. However, current research and development is attempting to increase production efficiency and sales by increasing rearing densities, improving diets, and increasing growth rates. As it is a hardy, fast-growing species that is tolerant to a wide range of environments and handling, it has become the dominant freshwater salmonid farmed in Europe and North America. Females are able to produce up to 2,000 eggs per kilogram of body weight, with most wild fish spawning once a year; however, selective breeding and photoperiod adjustment has developed hatchery strains that can mature earlier and spawn year round. Even with all that is known about the life history of
rainbow trout, research at one of the world's leading rainbow trout broodstock facilities showed that ~13% of females produce sub-fertile eggs, significantly decreasing expected production rates and thus revenue. If this problem could be solved, it would be a way to increase production and revenue without increasing stocking density and the negative side effects associated with doing so. Unfortunately, not much is known about the issue other than that it exists - this project would attempt to answer the "why" so that production could be safely increased and the findings applied to other species with the same problem. The overall objective of this project is to investigate the role of the stress hormone cortisol in sub-fertility using a whole-animal approach that investigates both the maternal hormone profile as well as embryonic viability. I am hypothesizing that chronically elevated
levels of circulating cortisol will negatively impact reproductive success, and thus facility productivity, of farmed female rainbow trout. I will test this hypothesis by injecting recently spawned farmed female rainbow trout with slow-release cortisol implants for four consecutive months of the twelve month reproductive cycle. Two additional groups will be implanted 4 and 8 months after spawning. I will collect blood samples every month during the implantation period and then sample blood and tissue every three months for the remaining time. At the time of ovulation, fish will be stripped of their gametes to determine whether or not they are sub-fertile and assess the survival of resulting embryos. The results of this study will provide insight on the cause of sub-fertility in farmed female rainbow trout and what changes could be made to improve facility production.