| Compensatory growth is a phase of accelerated growth when favourable conditions are restored after a period of growth depression. It reduces variance in size by causing growth trajectories to converge and is important to fisheries management, aquaculture and life history analysis because it can offset the effects of growth arrests. Compensatory growth has been demonstrated in both individually housed and grouped fish, typically after growth depression has been induced by complete or partial food deprivation. Partial, full and over-compensation have all been evoked in fish. But the studies on compensatory growth are far from enough. There is so much work to do to make the phenomenon of the compensatory growth clear. Effects and mechanism of temperature and nutrition stress on tongue sole, Cynolossus semilaevis Giinther were investigated in this study. The main results are as followings:1. The influence of temperature (16,19,22,25,28 and 31℃) on growth, biochemical composition and energy budget was investigated in juvenile tongue sole. The results showed that the specific growth rate of tongue sole increased with the increase of temperature from 16-25℃and then decrease at 28-31℃. The relationship between specific growth rate of juvenile tongue sole and temperatures was described as quadratic graph. Lipid and energy contents of dry body decreased with the increasing temperatures, while crude protein content was not significantly affected by temperature. The effects of temperatures on the energy budget of juvenile tongue sole were significant. Energy assimilated in growth and those consumed in respiration dominated the mode of the energy allocation of juvenile tongue sole. The proportion of food energy allocated to respiration increased with the increasing temperature. However, those assimilated to growth decreased with the increasing temperature. The present study revealed that the suitable temperature of juvenile tongue sole was 19-25℃. The mechanism of effects of temperature on the growth of tongue sole may be ascribed to the differences of food consumption and energy budget resulted from different temperatures.2. The influence of water temperatures (16,22 and 28℃) and ration levels (0%,25%, 50%,75% and 100% of satiation) on the growth, body composition and energy budget in juvenile tongue sole were investigated over 60 days. The specific growth rates of fish increased with increasing ration levels. Fish fed to 100% satiation at 22℃exhibited better growth than other treatments. The relationship among SGRW, SGRe, temperature (T) and ration (RLw, in weight and RLe, in energy) could be described by the regression equations:SGRW=20.778 log(RLw+5)-0.0767T-13.628, SGRe= 11.016 log(RLe+5)-0.152T-6.730. The maintenance ration levels were 0.19%, 0.46% and 0.74% of body weight, while 1.79%,3.21% and 4.94% of body energy at 16,22 and 28℃, respectively. Ration level from 50%-100% satiation did not influence food conversion efficiency. There is no significant difference in apparent digestion rate between fish fed to 75% and 100% satiation. The content of lipid in fish tended to increase with increasing ration levels, while tend to decrease with increasing water temperature. The crude protein content in fish tended to decrease with increasing ration levels at low temperature (16℃), while tended to increase at high temperature (22 and 28℃). The proportion of food energy assimilated in growth and the proportion consumed for respiration dominated the mode of the energy allocation of juvenile tongue sole. In the temperature range of this experiment, the proportion of food energy allocated to growth decreased with increasing temperature, and was not affected significantly ration level from 50%-100% satiation at the same temperature. The proportion of food energy consumed for respiration decreased with increasing ration, while increased with increasing temperature. The maximum of specific growth rate occurred in fish fed to satiation at 22℃, which suggested that commercial farmers could feed juvenile tongue sole to satiation at 22℃to obtain higher growth rate.3. The effects of starvation and re-feeding on compensatory growth, body composition, metabolism and energy budget were examined in juvenile tongue sole at 22℃for 64 days. Fish were divided into six groups including control group (continuously fed ad libitum group, C), starvation group (SO) and other four groups with food deprivation for 4 days (S1),8 days (S2),16 days (S3) and 32 days (S4), respectively. Fish in S1, S2, S3 and S4 resumed feeding after the corresponding starvation period. At the end of the experiment, the weight of S1 fish was highest but not significantly different with that of the control fish (P>0.05), indicating complete compensatory growth occurred. Although the specific growth rate in S2, S3 and S4 fish was greater than that in the control fish after re-feeding, S2, S3 and S4 fish did not reach the same body weight of the control fish at the end. Food conversion efficiency of tongue sole was significantly higher in S1 than in the control fish (P< 0.05). The feeding rate and apparent digestion in S2, S3 and S4 fish were significantly higher than those in the control fish, while no significant difference was found between S1 and the control fish. There was no significant difference among S1, S2 and C in the content of moisture, lipid, protein, ash and energy (P>0.05) at the end of the experiment. Upon re-feeding, metabolic rates of juvenile tongue sole increased rapidly except that there was a time lag appeared in nitrogen excretion for the fish starved for 32 days, and the peaks of these increases were directly proportional to the length of the starvation period. Estimated form energy budget during the period of the experiment, S1 fish exhibited significantly higher proportion of food energy assimilated in growth and significantly lower proportion consumed for respiration than the control fish (P<0.05). Based on the result of the present study, the underlying mechanisms for complete compensatory growth in juvenile tongue sole could be attributed to an improved energetic efficiency resulted from reduced metabolic expenditure during the period of recovery.4. The effects of previous food restriction on compensatory growth, body composition, metabolism and energy budget were examined in juvenile tongue sole at 22℃for 56 days. Fish were divided into five groups including control group (continuously fed ad libitum group, C), and the other four groups expressed as Group R0 (starvation group), R25, R50 and R75 were first fed at 0%,25%,50% and 75% of satiation, respectively for 14 days, and were then fed ad libitum for a recovery period of 42 days. There was no significant difference in body weight among R25, R50, R75 and the control group at the 6th,7th and 8th week. After re-feeding, the specific growth rate decreased with the increasing ration, but feeding rate increased with increasing ration. Food conversion efficiency of R0 fish was significantly higher than the control group in the 4th week to the 7th week(P<0.05). In the 4th week to the end of the experiment, there was no significant difference in the apparent digestion rate among all groups (P> 0.05). The oxygen consumption of R0 and R25 fish peaked after re-feeding, and then recovered to the level of the control group. The oxygen consumption of R50 and R75 fish were similar with that of the control fish. The moisture content of fish decreased with the increasing ration, which was similar with the ash content. The energy parameters in the control group were highest among all groups, but the proportions of food energy were not. It showed that the R25, R50 and R75 fish showed complete compensatory growth and the R0 fish showed incomplete compensatory growth. The growth compensation is mainly dependent on the different food restriction.5. A feeding experiment was conducted to examine the effects of repetitive periods of fasting and satiation feeding on the growth, body composition, metabolism and energy budget of juvenile tongue sole at 22℃for 72 days. There were five groups:the control fed ad libitum throughout the experiment (C); the treatment groups were subjected to repetitive periods of fasting and satiation feeding (2:4,4:8,8:16 and 12:24 days for group S2F4, S4F8, S8F16 and S12F24). The specific growth (SGR including SGRw, in terms of weight, and SGRe, in terms of energy) of C fish was significantly higher than those of other groups (P<0.05). There was no significant difference in body weight between S2F4 and C fish (P>0.05), and both of them were significantly higher than that of other groups. The apparent digestion rate of C fish was significantly lower than that of other groups (P<0.05). The energy digestion rate of C fish was not significantly different with S12F24 fish (P>0.05), but was significantly lower than the other three groups (P<0.05). The food conversion efficiency of S4F8 fish was significantly lower than that of S12F24 fish (P< 0.05). The feeding rate of control fish was the lowest (P<0.05). The protein content of fish decreased with the increasing cycle period. There was no significant difference in protein content between S2F4 and C fish (P>0.05). The oxygen consumption and ammonia excretion were lower in S2F4. The food energy of the control group was the highest (P<0.05). The food energy assimilated to metabolism in S2F4 fish was higher than that in C fish (P<0.05). It showed that the juvenile tongue sole of S2F4 showed complete compensatory growth. During the repetitive periods of fasting and satiation feeding, the juvenile tongue sole used protein as the first energy source.6. The effects of high and low water temperatures stress on the growth, body composition, blood physiology and energy budget of juvenile tongue sole was detected during 56 d experiment. There were seven groups:the control fed ad libitum throughout the experiment at 22℃(C); the other six treatments were reared at 16℃and 28℃for 1,2 and 3 weeks, respectively. Recorded as:A1, A2, A3, B1, B2, B3. The body weight of A1 and B1 were significantly higher than that of the control group (P<0.05). The SGRw of Al and B1 were significantly higher than those of other groups (P<0.05). The food conversion efficiency of fish underwent temperature stress increased and then decreased during compensatory growth. At the end of the experiment, there was no significant difference among treatments involved. Apparent digestion rate of fish suffered stress was higher than that of C fish at the later period of the experiment. At the end of the experiment, the moisture, lipid, ash and the body energy content of the fish was not significantly different with each other (P>0.05) except for the protein content. There was no significant difference of the food energy allocated to growth among C, B3 and B2 fish (P>0.05) which were significantly lower than that in other treatments (P<0.05). The food energy allocated to exertion and feces were highest in C. There were more FT3 at 16℃and 28℃in serum than at 22℃. In the fish at 16℃, the FT4 increased with the progress of the experiment. When the temperature returned to 22℃, the levels of the FT3 and FT4 in the serum clamed down to the level of the control group soon. It suggested that the fish in A1 and B1 showed over compensatory growth. The fish underwent temperature stress had reduced the metabolism and lifted the food conversion efficiency to complete their compensatory growth.7. The effects of high water temperatures and 25% ration stress on the growth, body composition and energy budget of juvenile tongue sole was detected during 56 d experiment. There were seven groups:the control fed ad libitum throughout the experiment at 22℃(C); the other six treatments were reared at 28℃and 25% ration for 1,2 and 3 weeks, respectively. Recorded as:B1, B2, B3, R1, R2, R3. The body weight of B1 was significantly higher than that of the control group (P<0.05) which was not significant with that of R1 (P>0.05). The SGRW of B1 were significantly higher than those of other groups (P<0.05). The food conversion efficiency of fish underwent temperature stress was superior to that of fish underwent food restriction. Apparent digestion rate of fish suffered stress was higher than that of C fish at the later period of the experiment. At the end of the experiment, the moisture, lipid, protein, ash and the body energy content of the fish were not significantly different with each other (P>0.05). There was no significant difference of the food energy allocated to growth among all treatments (P<0.05) except for B1 which was significantly higher than that of B3 and C. The energy lost in feces was higher in C than that in other treatments (P<0.05). There was no significant difference among all treatments of food energy allocated to exertion which was lowest in B1 (P<0.05). There was no significant difference among all treatments of food energy allocated respiration (P>0.05). It suggested that the fish suffered high temperature for 1 week showed over compensatory growth. And the fish in R1 showed complete compensatory growth. The fish underwent temperature stress had reduced the metabolism and lifted the food conversion efficiency to complete their compensatory growth. But the fish underwent food restriction lifted the feeding rate and food conversion efficiency more to achieve the compensatory growth.
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