Dietary selection by gilthead sea bream (Sparus aurata) provided with unbalanced mixed-macronutrient feeds dispensed from self-feeders

Abstract

We investigated dietary self-selection in gilthead sea bream using a multiple-choice self-feeding system. To this end, five groups of 15 fish (154g BW) were distributed among 500-l tanks and allowed to self-feed from 3 self-feeders, each of which distributed feeds composed of combinations of macronutrients. Three different selection ranges of protein (P), carbohydrate (C) and fat (F) (expressed as percentage of total macronutrients) were tested: in phase 1, PF (75%–25%, respectively), PC (75%–25%) and CF (85%–15%); in phase 2, PF (60%–40%), PC (75%–25%) and CF (60%–40%); and in phase 3, PF (60%–40%), PCF (20%–50%–30%) and PC (90%–10%). In addition, the effect of P deprivation on energy intake was tested. The results revealed that, despite the different selection ranges in each phase, the macronutrient composition of the selected diets did not differ significantly during the experiments, being on average 63.7±0.6% P, 15.5±1.7% F and 20.6±1.15% C. When sea bream were restricted to self-feeding on a protein-free diet for 10days, and were only given the CF (60%–40%) diet, the fish sustained their average energy intake (260.0±37.7kJ/kg BW/day), which did not differ statistically from the average energy intake during the previous three experimental phases (284.6±26.9kJ/kg BW/day). In conclusion, sea bream were able to compose and defend a balanced diet by selecting from three incomplete diets, and the fish were also able to maintain their energy intake for a short period of time when allowed to self-feed on a protein-free diet.