The thermal dependent biology of cultured lumpfish (Cyclopterus lumpus Linnaeus 1758): Differences due to temperatures during early life and how tolerance is measured

Abstract

The use of lumpfish as a “cleaner fish” in Atlantic salmon aquaculture is increasing. However, during the summer months, there have been large-scale mortalities of lumpfish at some North Atlantic salmon sea-cage sites. There is evidence that manipulating temperatures during early life can improve the thermal tolerance of fishes. Thus, we reared lumpfish embryos (eggs), larvae and juveniles under different temperature regimes, and measured their metabolic physiology and upper thermal limits, with the goal of better understanding their physiology and mitigating the effects of high summer water temperatures on their welfare. The specific incubation (egg) / rearing temperature combinations were 6 °C / 9 °C (normal production temperatures), 8.5 °C / 9 °C, 6–11 °C / 9 °C, 8.5 °C / 9–11 °C and 6–11 °C / 9–11 °C; with a range of temperatures indicating that fish were exposed to stochastic temperature changes.Hatching success was 61 % in the control (6 °C) group, as compared to ~47 % and 26.5 % in the groups exposed to 8.5 °C and the stochastic temperature regime (6–11 °C), respectively. Groups exposed to stochastic incubation and rearing temperatures also had the lowest survival rate (33.7 %) as opposed to those incubated and reared at constant temperatures (66.1 and 50.7 %) when unexpectedly exposed to high, and variable, ambient water temperatures that were experienced for roughly 7 weeks during rearing (due to abnormal water temperatures in the bay supplying our aquaculture facility). Interestingly, the critical thermal maximum (CTMax), incremental temperature maximum (ITMax) and metabolic capacity (i.e., aerobic scope) of 30-40 g lumpfish did not differ between the groups, and the first two parameters on average were 22.85 ± 0.12 °C and 20.63 ± 0.02 °C, respectively.