The economic viability of sea cage farming of Atlantic salmon is strongly influenced by the cost of
production of smolts. Understanding the mechanisms that contribute to, or cause reproductive failure in
spawning fish is an essential component of reducing those industry production costs, and at a broader
level, ensuring that there are sufficient smolts produced each year to maintain industry production. The
issue has been identified as an industry priority with the stated SALTAS aim of reducing the reliance on
repeat spawning fish for egg production. The potential cost of failing to solve the problem is high. The
survival of eggs to the eyed embryo stage can be as low as 30-50%, compared with 80% for eggs from
best performing fish (SALTAS data). Modelling of this cost gives direct increases in smolt production
costs of $225,000 per annum, but a potential industry shortfall in production terms of $15-20 million per
annum.
The knowledge gained through this research will be applied in a real life context to the Atlantic salmon industry in Australia to overcome a real and immediate industry bottleneck, and provide information to assist in large scale production procedures. It will provide important new information regarding the endocrine regulation of egg quality, information that could be highly relevant to other finfish industries, such as tuna and kingfish.
In addition to the direct benefit of this research to the Salmon industry, the investigation of the impact of temperature on reproductive process in fish is relevant to environmental studies concerning the impact of global warming on biological processes, with the Atlantic salmon being an example of a fish that has been translocated from a colder environment (Europe) to the warmer Tasmania.
Final report
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:
- Determine how temperature influences endocrine function and reproductive development in maiden and repeat spawning female Atlantic Salmon;
- Understand the molecular mechanisms that determine egg quality in broodstock maintained at elevated temperature; and
- 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.
