| Sea cucumber Apostichopus japonicus is one of the important economic culture species in northern China for its aphrodisiac and medical properties. Successful culture of this species requires a nutritionally adequate and economical diet. Protein is the most important nutrient component in aqua-feed and constitutes one of the primary nutrient costs of diets. Under the pressure of growing demand for fish meal, overfishing fishery caused the destruction of the ecological system and a dramatic rise in the price of fish meal. Therefore, it is irreversible to use coated amino acid to replace the fish meal included in the sea cucumber diets; and the study on essential amino acids in feed of sea cucumber is in a blank state. This study was designed to determine the dietary lysine requirement of sea cucumber Apostichopus japonicus juvenile focusing on growth performance, intestinal digestive enzymes, non-specific immune response and stress resistance, when the juveniles were fed the control diet used the fish meal and sargassum as protein source and five experimental diets containing graded lysine levels(D1: 0.28%, D2: 0.64%, D3: 1.19%, D4: 1.89% and D5: 2.32%), which supplemented with casein, gelatin and crystalline amino acid to substitute fish meal. The results are as follows:(1) In this trial, mean survival rate(SR) was generally low in all treatments, ranging from 68% to 87% and was unaffected by the dietary lysine level(P> 0.05); maximum FBW, WG and SGR were observed in sea cucumber juveniles fed the control diet. Except the control group, FBW, WG and SGR of sea cucumbers increased with increasing levels of lysine up to 1.19%, beyond which it showed a slight decling tendency, however, difference in these parameters were not significant(P> 0.05); FI of sea cucumbers fed the control and D3 were significantly higher(P<0.05) than that of juveniles fed diets D1, D2, D4 and D5.(2) Proximate body composition, except crude lipid, were unaffected by the dietary treatments(P> 0.05). The content of crude lipid increased with increasing dietary lysine levels, reached a maximum value at a dietary lysine level of 2.32%. There was no difference(P> 0.05) on total amino acid content of sea cucumber body wall among the treatment groups with exception of histidine, glutamic acid, glycine, alanine, tyrosine and indispensable amino acids.(3) Intestinal protease level increased with increasing dietary lysine level up from 0.28 to 1.19% and then decreased above the level. Whereas, the amylase activity was not affected by the experimental diets(P> 0.05).(4) ACP and SOD activities of the sea cucumbers were not affected by various dietary lysine levels, however, significantly(P < 0.05) higher AKP and CAT activities was observed in sea cucumbers fed 2.32% lysine diet than those of sea cucumbers fed the control and diet D1, D2, D3 and D4.(5) under the condition of acute temperature stress, the ACP activity of sea cucumber fed the control, D3 and D4 diet was significantly(P<0.05) higher than those of sea cucumbers fed D1, D2, and D5 diet and there was no significant(P> 0.05) differences among the control, D3 and D4 groups. The AKP activity of sea cucumber fed the control diet was significantly(P<0.05) higher than other groups. The CAT activity of sea cucumber fed the control diet was significantly(P<0.05) higher than those sea cucumbers fed D1, D2, D4 and D5 diet, but no significant(P> 0.05) differences were observed between the control and C groups.(6) Broken-line analysis on the basis of BWG shows that dietary lysine requirement of sea cucumber juveniles is 0.76% of the dry diet, corresponding to 5.43% of the dietary protein.From the view of growth performance of sea cucumber: lysine could be utilized from CAAs, however, sea cucumber utilize the CAAs-supplemented diet less efficiently than intact-protein diet.From the view of physiological and biochemical of sea cucumber: the sea cucumber fed the diet contain the lysine level from 1.19 to 1.89% has better nutritional value. |
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