2008/762 Understanding the molecular basis for improved egg quality in maiden and repeat spawning Atlantic salmon (Salmo salar) maintained at elevated temperature

By Kelli Anderson

Tasmanian Atlantic Salmon (Salmo salar) broodstock can encounter temperatures above 20°C, which has a marked negative effect on reproductive development. Broodstock management strategies are needed in order to maintain egg quality in the face of thermal challenge either due to seasonal fluctuation or climate change, where temperatures are expected to rise even further. In Tasmania, the Atlantic Salmon industry uses maiden fish for approximately 75 % of egg production due to their smaller size and the lower cost associated with their husbandry relative to repeats. However, maidens appear to be more susceptible than repeat fish to the effects of elevated temperature. The salmon industry's ability to cope with rising temperature is hindered by the lack of understanding of the effects of thermal challenge on the endocrine system, which ultimately determines egg quality.

Therefore the aims of the research were to:

1.  Determine how temperature influences endocrine function and reproductive development in maiden and repeat spawning female Atlantic Salmon;
2. Understand the molecular mechanisms that determine egg quality in broodstock maintained at elevated temperature; and
3. Develop management strategies to maintain endocrine function and egg quality under thermally challenging conditions.

The research provided evidence that female maiden Atlantic Salmon are more susceptible to the effects of elevated temperature and that thermal impairment of endocrine function occurs at multiple levels of the reproductive axis. Treatment with various hormonal therapies showed mixed results and suggest that it is difficult to overcome the impacts of higher temperature on the reproductive axis using a single hormonal treatment. Hormonal therapies in the future should simultaneously stimulate vitellogenesis and zonagenesis in order to maintain egg quality. It is evident that the method of hormonal delivery is of considerable importance and implantation techniques also warrant further investigation.