The oxygen threshold for maximal feed intake of Atlantic salmon post-smolts is highly temperature-dependent

In order to maximize the growth potential of Atlantic salmon (Salmo salar L.) in the on-growing phase in open sea cages, the dissolved oxygen (DO, % of air saturation) level must exceed the minimum DO required for maximal feed intake (DOmaxFI). The main aim of this study was to determine the effect of temperature on this important threshold DO, and secondly, to provide aquaculturists with a model that estimates feed intake as function of both temperature and DO. Quadruple tank groups of Atlantic salmon post-smolts (~ 0.3–0.5 kg) were kept at 7, 11, 15 and 19 °C, and subjected to seven DO levels per temperature, ranging from ≈ 32–92, 42–102, 52–112 and 62–122% O2, respectively, for 42 days. DO levels were changed every second day, in random order. Fish were fed a known amount of feed in excess twice daily, waste feed was collected and daily feed intake (DFI, % of biomass, BM, per day) estimated. The routine oxygen consumption rate (MO2 rout, measured in partially fasted and active fish) and the DO below which MO2 rout started to decline (termed the routine limiting oxygen saturation, LOSrout) was determined in fasted fish at all four temperatures at the end of experimentation, and the latter was used to estimate the “zero feed intake DO” in the DFI model. The data demonstrate sustained appetite with decreasing DO until a threshold level (DOmaxFI) is reached, at which point appetite gradually decreases. Both the maximal level of feed intake (DFImax) and the DOmaxFI were highly dependent on temperature, increasing from 0.47 to 0.88% of BM/day, and from 42 to 76% O2, respectively, within the temperature range tested. The LOSrout ranged from 24 to 40% O2. The present study is the first to present the pronounced effect of temperature on DOmaxFI, and results suggest that the DO requirement of A. salmon has previously been considerably over-estimated, particularly at lower temperatures. The study links growth performance to environmental temperature and oxygen.