A review of factors influencing maturation of atlantic salmon salmo salar with focus on water recirculation aquaculture system environments

Authors: GOOD, CHRISTOPHER - Freshwater Institute; DAVIDSON, JOHN - Freshwater Institute

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2016
Publication Date: 10/2/2016
Citation: Good, C., Davidson, J. 2016. A review of factors influencing maturation of atlantic salmon salmo salar with focus on water recirculation aquaculture system environments. Journal of the World Aquaculture Society. 47(5):605-632.

Interpretive Summary: Sexual maturation of Atlantic salmon Salmo salar is an extremely complex process, with many variables having the capacity to influence the timing and prevalence of maturation, and acting as promoters and/or inhibitors of sexual development. Early, or precocious, maturation reduces fillet quality and has the capacity to seriously impact production in commercial aquaculture settings, and in response there has been a significant amount of research devoted to understanding this issue in order to develop remedial strategies. Very little research has been conducted specifically examining salmon maturation in land-based, closed containment water recirculation aquaculture systems (RAS), which have recently received attention as an alternative technology for the sustainable production of market-size Atlantic salmon. Given the high prevalence of precocious maturation observed in the nascent closed containment aquaculture industry, and the potential economic challenges facing its expansion, it is imperative that best management practices are developed to reduce economic losses from maturation and other significant deleterious outcomes, in order to assist the sustainable growth of farmed Atlantic salmon production. This review provides a brief summary of published research on factors associated with early salmonid maturation, as well as information from research examining grilsing and growout performance of Atlantic salmon in closed containment aquaculture systems.

Technical Abstract: Maturation of Atlantic salmon Salmo salar is an extremely complex process, particularly in aquaculture systems, with many variables (known or otherwise) having the capacity to influence the timing and prevalence of maturation, and acting as promoters and/or inhibitors of sexual development. The vast majority of research carried out on salmon maturation in aquaculture has been in the context of the traditional industry; namely, land-based smolt production in freshwater systems, followed by transfer to sea cages for growout. Very little research has been conducted specifically examining salmon maturation in land-based, closed containment water recirculation aquaculture systems (RAS), which have recently received attention as an alternative technology for the sustainable production of market-size Atlantic salmon. Given the high prevalence of grilsing observed in the nascent closed containment aquaculture industry, and the potential economic challenges facing its expansion, it is imperative that best management practices are developed to reduce economic losses from maturation and other significant deleterious outcomes, in order to assist the sustainable growth of farmed Atlantic salmon production. This review provides a brief summary of published research on factors associated with early salmon maturation, as well as information on current practices applied in closed containment operations to minimize grilsing. In light of the novelty of raising salmon to market size in a closed containment environment, and the paucity of research on maturation in such environments, it is difficult at present to make specific recommendations to reduce grilsing in RAS; however, much-needed research can be directed, to an extent, based on findings made in more traditional settings. Among the numerous environmental variables influencing salmon maturation, photoperiod and water temperature are foremost; while photoperiod influences the “decision” to undergo or delay maturation (made months in advance), it is water temperature that ultimately determines the magnitude of maturation in a given salmon population. It is possible that current practices utilizing elevated water temperatures could be contributing to the problem of grilsing in closed containment; however, baseline research on water temperature, in conjunction with other variables such as salinity and feed energy content / fish adiposity, needs to be carried out in order to make definitive recommendations that will inform best management practices for closed containment salmon operations. Research is also needed on other potential influencers of maturation that are specific to RAS, such as the degree of exercise provided in circular tanks, the accumulation and impact of waterborne steroid hormones, and other water quality elements including endocrine disrupting compounds. It must be noted that key variables that may promote maturation are also associated with improved growth performance, and therefore recommendations to reduce maturation could be at odds with current production practices. Given the complexity of the overall problem, and this potential conflict between reducing early maturation and optimizing growth and feed conversion performance, the most expedient solution at present is for industry to partner with breeders to promote the availability of all-female germplasm for closed containment operators. There is already a possibility that all-female eggs will be available from a commercial supplier in Iceland beginning in late 2015, and if this becomes a reality (and all-female eggs are available to producers on a regular basis) it would avoid the significant research necessary to develop effective grilse reduction protocols in mixed sex populations. However, female grilsing, while not currently a major problem - but still present to a degree in specific operations - would also need to b