Production of market-size North American strain Atlantic salmon Salmo salar in a land-based recirculation aquaculture system using freshwater

A Review of Factors Influencing Maturation of Atlantic Salmon, Salmo salar, with Focus on Water Recirculation Aquaculture System Environments

“…In a follow‐up study under similar conditions, Berrill et al () determined that a longer (i.e., 12‐wk, versus 8‐wk) short‐day period to induce smoltification, begun in June as opposed to May, significantly reduced precocious parr observed later in the year. While the results of these studies are ultimately difficult to compare to more recent experimental closed containment growout trials (Davidson et al in press), they clearly demonstrate the importance of early rearing environmental factors, that is, photoperiod, temperature, or the interaction of these two parameters, on subsequent precocious maturation, and emphasis in future research should be applied to first‐year environmental conditions as maturation decisions are clearly made in the beginning at a very early age.…”

“…), the issue of precocious maturation has returned to the forefront among factors affecting production and profitability in these new operations. During Atlantic salmon growout trials conducted by the authors and colleagues (Davidson et al in press), precocious male maturation has been as high as 80% by harvest time at 4–5 kg in average weight. Anecdotally, early maturation has also been prevalent at other land‐based, closed containment facilities raising Atlantic salmon to market size (Table ).…”

“…The specific reduced photoperiod utilized in this study was LD16:8 (i.e., fish exposed to 16 h of light followed by 8 h of darkness). The impetus for examining a reduced photoperiod, versus continuous light, and its effects on early maturation, was twofold: (i) Atlantic salmon cohorts raised to market size in closed containment growout trials under continuous light have consistently produced a high percentage of maturing males, the most affected group demonstrating approximately 80% mature males by harvest at 24–26 mo posthatch (Davidson et al in press), and (ii) previously published research has suggested that a reduced photoperiod can reduce early maturation when compared with continuous light. The latter research includes the study by Fjelldal et al (), in which significantly higher proportions of mature males were observed in populations exposed to 3 mo of early rearing continuous light, versus those exposed to a natural photoperiod during this period; however, further analyses suggested that the continuous light treatment was acting as an “enabling factor,” whereas elevated water temperature determined the actual early maturation observed.…”

“…Although precocious parr were prevalent in all groups (ranging from 43.9 to 66.7%), LDN fish had a significantly higher proportion of mature parr, while the LD16:8 had significantly less mature parr than the other treatment groups. While precocious parr have not tended to be a significant issue during the early stages of closed containment growout trials (Davidson et al in press), mature underyearling smolts have been observed in very high numbers subsequent to being transferred to experimental‐scale RAS, compared with those remaining for commercial‐scale RAS growout (authors' unpublished data). Whether this unusually high incidence of early maturation was related to the sudden exposure to warmer water temperatures (ca.…”

“…While Atlantic salmon cultured using traditional farming practices are subject to seasonal ambient water temperatures (Kristensen et al ; Marine Harvest ASA ), salmon cultured in land‐based RAS are typically exposed to constant, albeit usually warmer, water temperatures that are targeted and maintained through various means of environmental control. Water temperature in an experimental near‐commercial‐scale RAS used for salmon growout by the authors and colleagues has been controlled by adding more or less cool (12–13 C) spring water depending on the season, with greater volumes of spring water used during the summer months to chill the culture water and less spring water added during the winter months to retain heat (Summerfelt et al ; Davidson et al in press). This temperature control regime has been applied to maintain optimal and consistent temperatures for salmon growth of 15–16 C year round.…”