Warming waters and scarce meals: how temperature and food availability impact Arctic cod (Boreogadus saida) growth and autumn reproductive investment

Rapid warming of Arctic seas and expected food web shifts may force fish to adjust energy allocation strategies that balance growth with future survival (lipid storage) and reproductive success (gonadal development). In a laboratory study, we investigated combined effects of temperature and food ration on energetics of adult Arctic cod ( Boreogadus saida ) during the critical autumn-winter transition period in a laboratory setting. We compared specific growth rate (SGR; mass%/day), hepatosomatic index (HSI; %), and gonadosomatic index (GSI; %) of fish kept at three distinct temperatures (0, 3, and 8°C) for 12 weeks and fed either low (1% dry weight/day) or high (4% dry weight/day) rations. Female gonad development stages, as well as lipid profiles of tissues, were also compared across treatments. Throughout the experimental period, energy storage in the liver was reduced while more energy was invested into reproduction. Somatic condition and tissue lipid storage were lowest at the warmest temperature (8°C). Muscle tissue from fish held at 0°C and fed high rations contained higher total lipids (μg/mg wet weight) compared to fish held at 8°C and fed low food rations. Gonads from females that were held at 3°C and fed high rations contained higher total lipids and major lipid class concentrations than those of females from the other two temperature treatments, regardless of ration. Overall, growth and energetic allocation in Arctic cod were influenced by both temperature and food availability, suggesting that these factors are potential drivers of the timing and magnitude of winter spawning in this key ecological species.