Influence of dietary fat and adiposity on feed intake of juvenile red sea bream Pagrus major

Abstract

A two-phase experiment was conducted to examine the effects of dietary fat and adiposity on feed intake of red sea bream. In Phase 1, juveniles (9.7 g, 20 fish tank −1, 4 replicates) were fed low fat (LF; 15.3% fat, 60.6% protein, 22.2 kJ g −1 energy, 0.61 g ml −1 density) or high fat (HF; 24.6% fat, 54.9% protein, 24.2 kJ g −1 energy, 0.68 g ml −1 density) diets for 4 weeks to produce fish which differed in adiposity. In Phase 2, all groups were fed the LF and HF diets alternately for 8 days. Fish were fed to apparent satiation by hand twice daily and daily feed consumption was recorded. Fish were weighed at the start, weekly during Phase 1 and at the end of Phase 2. Proximate composition was determined at the start of the experiment and after Phase 1 and 2. In Phase 1 the amount (18.6±0.35 vs. 17.1±0.19 g) and volume (30.6±0.58 vs. 25.2±0.28 ml) of feed consumed was significantly greater in fish fed the LF diet; energy intakes (LF, 412±7.8; HF, 413±4.7 kJ) and terminal mean fish weights (LF, 28.2±0.5; HF, 27.7±0.1 g) were similar. Fish fed the HF diet had a significantly higher proportion of visceral (37.6±1.5 vs. 28.9±1.2%) and carcass fat (9.7±0.3 vs. 8.0±0.3%). In Phase 2, fish fed the LF diet in Phase 1 consumed more of both the LF diet (2.9±0.2 vs. 2.4±0.1 g, P<0.05) and HF diet (3.2±0.1 vs. 2.9±0.1 g, P<0.07). Within each treatment fish consumed equal volumes of HF and LF feed, but the fish fed the LF diet in Phase 1 consumed a significantly greater total volume of feed (9.5±0.4 vs. 8.1±0.3 ml). Fish weights at the end of Phase 2 did not differ (LF, 34.6±0.9 vs. HF, 33.8±0.4). Our results indicate that the fish ate to meet an energy demand during Phase 1 and suggest that stomach volume increased in fish fed the lower energy (LF) diet, allowing increased meal size. This increase in meal size persisted when these fish were fed alternating HF or LF diets for 8 days (Phase 2). We were unable to unequivocally demonstrate an effect of adiposity on appetite during Phase 2, although this can be inferred since the fish fed the HF diet in Phase 1 should also have had the ability to increase their feed intake during Phase 1, but did not.