Institute of Aquaculture
Heat is off How low should you go with incubation temperatures for triploid salmon? THE demand for salmon is growing and in order for the industry to keep pace, we must adapt accordingly. Triploid Atlantic salmon have the potential to play an important role in the developing aquaculture industry. The fish are rendered sterile which can combat escapees from breeding with wild populations and also enhance growth potential. However, triploid salmon have previously been associated with a higher prevalence of bone malformations. Egg incubation temperature appears to be of particular importance, as triploids are thought to be more sensitive to temperature than diploids, and embryogenesis is a critical developmental onset. This has been studied as part of Michael Clarkson’s PhD , sponsored by Marine Harvest Scotland, BioMar and the IoA, under the supervision of Dr John Taylor and Prof Herve Migaud. The present project investigated the development of diploid and triploid salmon reared under different incubation temperatures (6, 8, or 10°C) during either a short (pre-hatch) or long (up to first feeding) window. Reducing egg incubation temperatures slows down development, which may be problematic for a well established commercial production cycle. The aim of the trial is to refine husbandry regimes during early egg incubation in salmon to promote optimal development and performance later on, and produce more robust stocks, while keeping in mind the production cycle duration. Such regimes are based on a deeper understanding of the underlying effects of temperature on key physiological functions in salmon, including the regulation of selected genes involved in bone and muscle development. Top: Salmon eyed eggs. Temperature is a very important factor during embryAbove: Michael Clarkson ogenesis in all animals. Humans and other mammals have the ability to regulate their internal temperature, whereas fish are directly influenced by the temperature of their surrounding environment, the definition of an ectothermic animal. This has been utilised to increase production of farmed salmon by speeding up development using elevated temperatures. Decades of research and industry experience has found 8 °C to be the upper threshold for optimal egg incubation temperature for a normal diploid population. Research into the use of triploid salmon in aquaculture has suggested that these individuals have very different nutritional and environmental requirements compared to their diploid siblings. Triploid specific diets have been developed and husbandry protocols have been adapted which have certainly reduced the negative attributes historically associated with triploid salmon. However, current research is demonstrating that increased prevalence of bone malformations in triploid
salmon can be pre-determined prior to first feeding in alevins, and then manifests itself later during grow-out. Thus, it is likely that triploids have a lower thermal tolerance than their diploid siblings and only recently has this been considered during the embryogenesis stages. Overall, this study showed that incubating eggs at 6°C had positive effects on the development of both diploid and triploid Atlantic salmon. This simple husbandry refinement allowed the fish to utilise their yolk sac more efficiently and grow better, and it also result in a lower occurrence of spinal health problems in later life stages. However, it would extend the duration of a conventional production cycle. For example, incubating under a conventional protocol at 8 °C from fertilisation until first feeding takes roughly 16 weeks. If this temperature was lowered to 6 °C, that would be extended to 21 weeks. If we can incubate at 6 °C for only a short window, prior to hatching, this can both allow for the improved robustness of the fish with only minimal impact on the duration of egg incubation (18 weeks). These results are very encouraging for triploid Atlantic salmon aquaculture. They contribute to a better understanding of how climate change and the seasonal warming of water bodies would impact on fish development and robustness in wild populations. For further details, contact Michael Clarkson (mc63@ stir.ac.uk), Dr John Taylor (email@example.com) or Prof. Herve Migaud (firstname.lastname@example.org).
These results help understand how climate change would impact on fish development and robustness in wild populations
Institute of Aquaculture
Institute of Aquaculture, University of Stirling