Experimental Studies On Individual Variation In Growth And Causes In Sea Cucumber, Apostichopus Japonicus

1 The present studies deal with the intra-specific effects of sea cucumber Apostichopus japonicus with unlimited food resources, especially the effects of stocking density on growth variation of the animal and energetic changes of small individuals under the stress of large individuals. The results showed that with the initial body weight of 5.12±0.09-6.11±0.26g of sea cucumber among the densities of 5,10,20,30,40 and 50 ind./100L, the density of 20 ind./100L was the optimum stocking density because of its highest specific growth rate, crude protein content and crude lipid content in tissue. Individual growth variation of A. japonicus increased with the increase of stocking densities, whereas no significant differences in the variation were found when the density was over 30 ind./100L (P>0.05). The low-weight individuals under the stress of heavy-weight individuals exhibited obvious changes in energetics, such as lower ingestion rate, lower energy deposited as growth but higher respiration and excretion. The coefficient of variation (CV) in growth of the animals was over 70% due to simultaneous action of aggression and maybe a factor of chemical mediator, and led to significant changes in energetics of small size individuals.2 The present studies were conducted to elucidate the effects of large individuals of sea cucumbers Apostichopus japonicus Selenka on the physiological performance of small individuals of sea cucumbers by measuring growth, respiration, excretion, Na+/ K+-ATPase, pyruvate kinase and hexokinase. After certain time of cultivation an obvious size differences were seen among the sea cucumber individuals in different treatments. The results showed that with sustainable food supply and under the "stress" of large-size A. japonicus, the SGRs of the small-size ones became negative in values, their oxygen consumption rates and ammonia excretion rates were significantly lower than those of the big-size A. japonicus (P<0.05); The small-sizes individuals under the "stress" of big-size individuals exhibited obvious changes in physiological performance, such as, the Na+/K+-ATPase activity enhanced significantly (P<0.05), HK activity and PK activity reduced significantly (P<0.05), which implies that the glycolysis pathway of small-sizes individuals might be inhibited to some extent by the "stress" of big-sizes individuals. The aggression behavior of A. japonicus was not seen obviously during the experiment. However, the small-size individuals under the "stress" of big-size individuals exhibit some changes in physiological performance.3 The exceptionally large individual growth variation has been previously recognized in several sea cucumber cohorts. However, there is a lack of information regarding the mechanism of such individual differences. In this study, the sea cucumber Apostichopus japonicus (Selenca) was reared individually in order to eliminate possible effects of social interaction, stocking density, etc. The results showed that there were substantial differences in growth among the sea cucumber individuals during the 100-day experiment. The special growth rate of the sea cucumber individuals differed by up to three folds (from 0.40% to 1.01%), and the coefficient of variation in body weight increased from 12.04% to 40.51%. The final body weight, food intake and food conversion efficiency for each sea cucumber were generally positively correlated with their initial body weight (P<0.05). Energy budget of the animals showed that the food energy spent on respiration was much greater (about four folds) but energy deposited to growth was much less for (initially) smaller than for larger A. japonicus. The present result implies that there are obvious genetic differences among the sea cucumber individuals, largely accounting for the individual growth variation of the cohort sea cucumber. These results will provide some basic data for promoting selective breeding and farming of the sea cucumber. 4 The present study deals with the effects of social hierarchy on individual growth variation of sea cucumber. All cohort sea cucumbers were size-graded and divided into two groups, i.e. the heavy-size (H) A. japonicus group (initial body weight 10-12g) and the light-size (L) A. japonicus group (initial body weight 3-4g). Six social hierarchy treatments of A. japonicus, i.e. the heavy-size (H) A. japonicus:the light-size (L) A. japonicus 0:20,2:18,4:16,6:14,8:12 and 10:10 ind/160L fiberglass tank (represented as A, B, C, D, E and F, respectively) were used in this trial. The results showed that:(1)there were obvious social structures among individuals A. japonicus, and the heavy-size A. japonicus was the first rank (dominant, H), the L-big size was the second rank (Lb) and the L-small size was the third rank (subordinate, Ls). (2)The Ls A. japonicus showed a negative growth under the double "stress" of the H and Lb A. japonicus. The maximum value of SGR occurred in the Lb A. japonicus of A treatment and reached 1.25%d-1, which was significantly higher than those in other treatments (P<0.05). (3)The CVs for the body weight of H and L A. japonicus were significant difference during the 80-day's trial, and the CVs for the body weight was positively correlated to the experiment time (P<0.05). The maximum value of CVs for the body weight occurred in the A treatment and reached 61.4%. (4)Under the 80-day's experiment, the biochemical composition of H, Lb and Ls A. japonicus exhibit obvious changes. With the number of H A. japonicus increasing, the crude fat contents and the crude protein contents of Lb and Ls A. japonicus decreased, and the crude ash content increased. So in sea cucumber aquaculture practice, it will be effective to alleviate the "stress" of the dominant individual, improve production and size uniformity by size grading periodically.5 The present studies were conducted to elucidate the effects of social hierarchy on the physiological performance of dominant and subordinate individuals of sea cucumbers Apostichopus japonicus Selenka by measuring respiration, excretion, metabolic enzymes and digestive enzymes. All cohort sea cucumbers were size-graded and divided into two groups, i.e. the heavy-size (H) A. japonicus group (initial body weight 10-12g) and the light-size (L) A. japonicus group (initial body weight 3-4g). Six social hierarchy treatments of A. japonicus, i.e. the heavy-size (H) A. japonicus:the light-size (L) A. japonicus 0:20,2:18,4:16,6:14,8:12 and 10:10 ind/160L fiberglass tank (represented as A, B, C, D, E and F, respectively) were used in this trial. The results showed that:(1)there were obvious social structures among individuals A. japonicus in the physiological function, and the heavy-size A. japonicus was the first rank (dominant, H), the L-big size was the second rank (Lb) and the L-small size was the third rank (subordinate, Ls). (2)The oxygen consumption rates and ammonia excretion rates were positively correlated to social hierarchy of A. japonicus (P<0.05), and were shown in descending order as followed:H>Lb>Ls; Meanwhile, with the "stress" of the number of H-size A. japonicus increasing, the oxygen consumption rates and ammonia excretion rates of the Lb and Ls A. japonicus exhibited significantly decreased (P<0.05). (3)The H and Lb size A. japonicus were all in the physiological activity stage because of their highest activities of metabolic enzymes and digestive enzymes. However, the Ls size A. japonicus under the double "stress" of H and Lb size individuals exhibited a metabolic and digestive disturbance period, such as the lowest activities of metabolic enzymes and digestive enzymes. So in sea cucumber aquaculture practice, this study reconfirmed that it will be effective to alleviate the "stress" of the dominant individual in the physiological functions, and it will be necessary to improve production and size uniformity by size grading periodically.6 Specific growth rate, food intake rate and energy allocation of Red and Green Apostichopus japonicus were studied in both individual housed and group housed treatments in order to compare the growth performances of the two variants and to elucidate quantificationally the mechanism of their individual growth variation. The results showed that the growth rate of Red variant was significantly higher than that of Green variant in most treatments after 120-day's trial (P<0.05). Red variant had higher food intake rate and less percentage of energy lost in respiration than Green variant, and the coefficient of variation for body weight of the former was significantly lower than that of the latter (P<0.05). The value differences of the coefficient of variation for body weight of Red and Green variants between the continuous individual-housed treatment and continuous group-housed treatment were 11.56 and 19.32, respectively. The value differences were less than the corresponding values in the continuous individual-housed treatment (25.90% and 41.91%, respectively). The results indicate that the inherent factor is more important than the intra-specific competition in the contribution to the individual variation of A. japonicus in growth.7 In this study, we determined the activities of pyruvate kinase (PK), hexokinase (HK), lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) and the content of lactic acid (LD) in the body walls and muscles of Red and Green variants of sea cucumber Apostichopus japonicus respectively, which were reared under individual and group housing in order to analyze the effects of different culture modes on the physiological performance of sea cucumbers. The results showed that under different treatments, the activities of PK, HK and MDH in the body wall and muscle of Red variants were higher than those of Green variants, especially in the Ab treatment (P<0.05). However, the LDH activity in the muscle of Red variants was slightly higher than that of Green variants, but the difference was not significant (P>0.05). The LDH activity of Red variants in the Ab and Ba treatment was higher than that of Red ones in the Aa and Bb treatment, but Green variants were contrary. The maximum value of the LD content of Red and Green variants occurred in the Ab treatment, and the LD content of the body walls and muscles of Red individuals was higher than that of Green, especially in the body walls (P<0.05). So in sea cucumber aquaculture practice, it reconfirmed that the re-grouped housing mode will be propitious to the physiological positive responses, and it will be effective to improve production and size uniformity by meeting the needs of higher growth and higher metabolize.