Introduction
The onset of sexual maturation in Atlantic salmon is a highly flexible process, with numerous environmental factors capable of influencing this process. Mature salmon are undesirable for aquaculture producers for several reasons, including the reduced value of the consequently downgraded product. Recirculating aquaculture systems (RAS) are increasingly being utilized to produce smolt, post-smolt, and even harvest-sized Atlantic salmon; however, RAS environments have been associated with increased prevalence of precocious maturation in Atlantic salmon populations. Among other things, it has been speculated that the relatively higher water temperatures of RAS could provide the necessary environmental cue to induce sexual maturation . We sought to investigate this area through two experiments, (i) assessing the prevalence of maturation in post-smolt salmon raised in replicated freshwater RAS at either 12 o C or 14 oC , and (ii) determining whether there is a size threshold at which post-smolts exposed to an increase in water temperature from 12 o C or 14 oC will exhibit increased levels of sexual maturation. This presentation will discuss the findings of these studies and their ramifications for RAS production of post-smolt Atlantic salmon.
Materials and methods
Study 1. Mixed-sex diploid Atlantic salmon (approximately 50 g in weight, 243 days post-hatch in age) were stocked into six replicated RAS , three operated at 12 o C and three at 14 o C; salmon were raised at these temperatures under controlled conditions until final sampling at 489 days post-hatch (mean weight 1,323 g) , at which time all fish were assessed for maturation via typical external signs, and gonadosomatic indices . Study 2. Post-smolt Atlantic salmon raised at 12 oC were stocked into 12 replicated tanks in a flow-through system , with three random tanks receiving an elevation in temperature from 12 o C to 14 o C at time points corresponding to source population mean weight reaching 100 g, 150 g, 250 g, and 350 g. All salmon were subsequently raised to a mean weight of approximately 600 g, after which maturation was assessed via gonadosomatic indices.
Preliminary Results
At the time of abstract submission (July 2021) , Study 1 data are still being analysed, while Study 2 is ongoing and scheduled to conclude in August 2021. All final results will be presented and discussed in depth at Aquaculture Europe 2021. Pr eliminary results from Study 1 suggest that maturation was significantly (p<0.05) reduced in RAS operated at 12 o C vs. 14 oC, although maturation was still relatively prevalent ( approximately 20% of the population) in the 12 o C treatment group. External evaluations of typical maturation signs (kype, color, ovipositor, etc.) correctly predicted maturation status, as assessed through gonadosomatic indices, >94% of the time.