Abstract:Sipunculus nudus juveniles at average body weight of (15.50±0.04) mg were fed diets at seven lipid levels (0.36%, 3.32%, 6.48%, 9.31%, 12.16%, 15.14%, and 18.36%) respectively for 8 weeks to investigate the effects of dietary lipid levels on their growth performance, body composition and digestive enzyme activities. It was found that lipid levels significantly affected growth performance of juvenile S. nudus (P<0.05). With the increased of dietary lipid levels, the weight growth ratio (WGR) and specific growth ratio (SGR) of peanut worm were firstly increased and then decreased, and when the dietary lipid level was 9.31%, both WGR and SGR produced the maximum value. The regression model analysis showed the best dietary lipid level which could acquire the best WGR was 8.70%.The results of body composition analysis showed that dietary lipid levels had significant effects on body lipid and protein content. Body lipid content increased with increase of dietary lipid. S. nudus fed with 18.36% lipid produced the highest body lipid content, which was significantly higher than those fed on lower lipid levels (0.36%, 3.32%, 6.49%, 9.31% and 12.16%) (P<0.05). There was a downward trend in body protein content with the increase of dietary lipid, and when it reached 18.36%, the body protein content was significantly lower than that those seen in treatments with lower lipid levels (P<0.05). The dietary lipid levels had no significant effects on moisture and ash content of the worm (P>0.05). With the increasing doses of dietary lipid levels, the protease activity and the lipase activity were firstly increased and then decreased. Both protease activity and the lipase activity produced the maximum value when the worms were fed with diet containing 9.31% lipid. But the dietary lipid levels had no significant effects on amylase activity of S. nudus (P>0.05). Based on comprehensive analysis of WGR, it is suggested that the suitable dietary lipid level for juvenile S. nudus is 8.70%.
