Utilization Of Carbohydrate By Juvenile Peanut Worm (Sipunculus Nudus)

Three feeding trials were conducted to investigate the effects of different dietary carbohydrate sources, carbohydrate levels and carbohydrate/lipid ratios on the growth performance, body composition and digestive enzyme activities of peanut worm, Sipunculus nudus, which is the most important cultured marine species in southern China.1. An8-week feeding experiment was conducted to investigate the effects of different dietary carbohydrate (CBH) sources on growth, body composition and digestive enzyme activities of juvenile peanut worm, Sipunculus nudus. Seven isonitrogenous and isolipidic diets were formulated to contain different CBH sources (glucose, sucrose, dextrin, tapioca starch, potato starch, corn starch or gelatinized corn starch). The results showed that the group which fed with gelatinized corn starch has the highest weight gain rate (WGR) and specific growth rate (SGR), and were significantly higher than other CBH dietary (P<0.05). However, the dietary CBH sources had no significant effects on survival rate (SR) of S. nudus (P>0.05). The results of body composition analysis showed that different CBH sources had significant effects on body moisture and body protein (P<0.05).The S. nudus fed with glucose had the highest body moisture and the lowest body protein, which were significant different from the others. No significant differences were observed in lipid content and body ash content of S. nudus among dietary treatments with different CBH dietary (P>0.05). Different CBH dietary had significant effects on digestive enzyme activities of S. nudus (P<0.05). The sucrose group expressed the highest protease activity and amylase activity, and was significantly different from other CBH treatments. However, the highest lipases activity was found in the group fed with gelatinized corn starch. It could be concluded that the ablity for S. nudus to utilize macromolecular carbohydrates was better than that to utilize small molecule carbohydrates, and pre-gelatinization of corn starch significantly improved corn starch utilization in S. nudus from the experiment results.2. An8-week feeding experiment was conducted to investigate the effects of different dietary carbohydrate (CBH) levels on growth, body composition and digestive enzyme activities of juvenile peanut worm, Sipunculus nudus. Six isonitrogenous and isolipidic diets were formulated to contain different CBH levels (1.89,7.35,12.81,18.27,23.73or29.19%). The results showed that the dietary CBH levels had no significant effects on SR of S. nudus (P>0.05). However, with the increasing of dietary CBH levels, WGR and SGR increased when dietary CBH content were between1.89%and18.27%, and then decreased significantly with dietary CBH further increased (P<0.05). The results of body composition analysis showed that dietary CBH levels had significant effects on body protein and lipid content (P<0.05). No significant differences were observed in body moisture and body ash contents of S. nudus among dietary treatments with graded levels of CBH (P>0.05).With the increasing of dietary CBH levels, the body protein content were firstly increased and then decreased, and when the dietary carbohydrate level was23.73%, body protein content produced the maximum value. There was an upward trend in body lipid content, and when the dietary carbohydrate level was29.19%, the body lipid content produced the maximum value. CBH levels significantly affected protease activity and amylase activity of S. nudus (P<0.05). Both protease activity and amylase activity were firstly increased and then decreased with the increased of dietary CBH levels, and they produced the maximum value when the dietary CBH level was23.75%and18.27%, respectively. However, the dietary CBH levels had no significant effects on lipases activity of S. nudus (P>0.05). The regression model analysis showed the best dietary CBH level which could acquire the best WGR was18.52%.3. An8-week feeding experiment was conducted to investigate the effects of different dietary carbohydrate/lipid (C/L) ratios on growth, body composition and digestive enzyme activities of juvenile peanut worm, Sipunculus nudus. Five isonitrogenous and isoenergetic diets were formulated to contain different carbohydrate/lipid (C/L) ratios (0.68,1.02,1.62,2.61or4.35). The results showed that the dietary C/L ratios had no significant effects on SR of S. nudus (P>0.05). With the increasing of dietary C/L ratios, WGR and SGR increased when dietary C/L ratios were between0.68and2.61, and then decreased significantly with dietary C/L ratio further increased. When the dietary C/L ratio was2.61(CBH level=20.64%, while lipid level=7.92%) both WGR and SGR produced the maximum value. The dietary C/L ratios had significant effects on body moisture, body protein content and body lipid content (P<0.05), but no significant effects on body ash content of S. nudus (P>0.05). Body lipid content of S. nudus significantly increased as C/L ratio decreased (P<0.05). However, body moisture and body crude protein content of S. nudus significantly increased as C/L ratio increased (P<0.05). Different C/L ratios had significant effects on amylase activity and lipases activity of S. nudus (P<0.05), but no significant effects on protease activity (P>0.05). The regression model analysis showed that the most suitable dietary C/L ratio in the S. nudus was2.42.