| Compensatory growth is a hot area of fish nutrition-physiological research, and studies in this area can help us to know the characteristic, rule and physiological mechanism of compensatory growth in fish, provide theoretical foundation for fish growth research, it can also improve feed conversion rate and aquaculture production service, reduce the cost of production and labour force.This experiment was conducted to evaluate the effects of cyclical starvation and refeeding on growth performance, feed utilization, body compositions, digestive enzyme activities and biochemical indices of juvenile black sea bream (Acanthopagrus schlegelii). The aims of this research were to determine the type of compensatory growth and preliminary discuss its mechanism in the progress of cyclical starvation and refeeding of fish.The healthy and uniform juveniles black sea bream in the same batch were randomly allotted to five groups with triplicate of 25 fishes (average initial body weight:9.56±0.12g, mean±S.D.) and the feeding trial last for 56 days. Feeding treatments consisted of the following five regimes of 1-week duration:satiate feeding (S0), S1, S2, S3 & S4 experienced 0,1,2,3 and 4 days of starvation then feeding to apparent satiation for the remainder days, respectively. Fishes were weighted once every two weeks and then killed to collect samples for analyses in the end of the experiment.The results showed that cyclical starvation and refeeding had no significant effect on survival rate (P>0.05); weight gain (WG), specific growth rate (SGR) were the highest of fish in S1 group (P<0.05). The S2 group had no significant difference with the control group (P＞0.05), but significantly higher than that in S3 and S4 groups (P<0.05); condition factor (CF), intraperitoneal fat ratio and hepatosomatic index (HSI) showed decreasing trend, but there were no significant difference among the S0, S1 and S2 groups (P>0.05).The feeding rate (FR) were gradually increasing with the increasing starvation days of every week (P＜0.05). The feed efficiency (FE) and protein efficiency rate (PER) were the highest of fish in S2 group (P＜0.05), which was significantly higher than all the other groups except of the S1 group. The WG of S1 group showed over-compensatory growth, which was significantly higher than that of fish in the control group (P<0.05); The difference between the S2 group and the control group were insignificant (P>0.05), thus the S2 group had completely compensatory growth; The value of WG in S3 and S4 groups were lower than the control group, but had higher FR, which the two groups showed partly compensatory growth.The apparent digestibility coefficients (ADCs) of dry matter increased until reached the highest level in S3 group which was higher than all the other groups with exception of S2, then decreased. The ADCs of crude protein presented descent trend with the increasing starvation days of every week. The ADCs of crude protein in S1 group was significantly higher than that of fish in S3 and S4 groups (P<0.05), while it was not significantly different with that of fish in SO and S2 groups (P>0.05). The ADCs of crude lipid was not affected by different starved days per week significantly (P>0.05).The cyclical starvation and refeeding treatment had no significant effects on ash content in whole fish body and muscle (P>0.05). The moisture content of whole fish presented an increasing tendency with the increasing starvation days of every week, the content in SO, S1 and S2 groups were without significant difference (P>0.05), but were significantly lower than those of fish in the S3 and S4 (P＜0.05). The crude protein and crude lipid in whole fish body showed decreasing trend, but the differences among the SO, S1 and S2 groups were insignificant (P>0.05), however, the values were all significantly higher than those of fish in the S3 and S4 groups (P<0.05). The moisture content of muscle presented an increasing tendency with the increasing starvation days of every week, but the difference among the S0, S1, S2 and S3 groups were insignificant (P＞0.05), however the values were all significantly lower than that of in S4 group (P<0.05). The muscle crude protein and crude lipid presented decreasing tendency with the increasing starvation days of every week, but the difference among the SO, S1 and S2 groups were insignificant (P＞0.05).The total protein, glucose, unsaturated fatty acid in serum of experimental black sea bream showed declining trend, but there were no significant differences among the S0, S1 and S2 groups (P>0.05). The content of triglyceride and cholesterol in serum were gradually decreasing, the S1 group had no significant difference with the SO group (P>0.05). The concentration of growth hormone (GH) showed decreasing tendency with the increasing starvation days of every week, no significant difference were observed among S2, S3 and S4 groups (P>0.05), but the concentrations in these groups were significantly higher than those of fish in SO and S1 groups (P＜0.05); The concentration of triiodothyronine (T3) reduced gradually, the concentrations in S0, S1 and S2 groups were significantly higher than those of fish in the S3 and S4 groups (P＜0.05).The protease and lipase activity of liver, stomach, anterior gut and middle gut of fish in S2 group were significantly higher than that of fish in other treatments (P＜0.05). The stomach had the highest protease activity (P＜0.05), while the anterior gut had the highest lipase activity (P＜0.05). The amylase activity of liver, stomach, anterior gut and middle gut presented the similar trend, which reached the highest level of fish in S3 group (P＜0.05), the highest amylase activity was observed in the liver among these tissues.Using paraffin section technique, hematoxylin-eosin staining and electron microscopy, the effects of cyclical starvation and refeeding on the histological structure of stomach and gut were examined. Results showed that starvation over 2-days per week would cause gastric body, mucosa and gland shrink, as well as gastric gland arranges disorder and its secretory granules decrease evidently. The muscular layer becomes thin and muscle fibers arrange loosly. The changes in the anterior segment of gut structures and functions were found. The intestinal villi and epithelium cells becomes shorter and thinner and decreases quantitatively while striated border deteriorates and the number and volume of goblet cells reduced. Histological structure of stomach and gut were unaffected by starved two days per week during the progress of cyclical starvation and refeeding.Based on growth performance and feed efficiency in the present study, at the water temperature 28±1℃, juvenile black sea bream could starved for two days per week without any adverse effect, and fish starved for one day per week showed superior grow rate and feed utilization. The conclusion from current research would be useful for reducing the cost of feed and elevate cultivation benefit in black sea bream.
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