| 1The present study was conducted to investigate the effects of physical contact on thegrowth of Apostichopus japonicus through various stocking densities, group cultureand physical isolation culture. The results showed that the specific growth rates(SGR), the feed conversion efficiencies and the energy used for growth of the animaldecreased with the increase in stocking density, while the coefficient of variations(CV) in group culture treatments increased. In high density treatments (4,6ind./40L),the SGRs in isolated culture treatments were not different to those in group culturetreatments of the same density, however the CVs in the latter (58.0%and60.4%,respectively) were significantly higher than those in the former (37.8%and35.8%,respectively). The CV difference between group one and isolated one of the samedensity (20.2%and24.7%, respectively) was less than that in single individual culture(32.7%), indicating that the effect of physical contact on growth variation was weakerthan that of genetic factor. This study proved that the individual growth variation insea cucumber resulted mainly from genetic factor and physical contact, while somechemical mediator might also be the factor affecting the growth rate of sea cucumber.2The present study was conducted to investigate the effects of stocking density andphysical contact on the physiological performance of Apostichopus japonicus throughvarious stocking densities, group culture and physical isolation culture. There wereeight treatments and each treatment had four replicates in this experiment. Group1,3,5,7were isolated culture treatments and stocking density were1,2,4,6ind./40L,respectively; Group2,4,6,8were group culture treatments and stocking density were2,4,6,8ind./40L, respectively. The experiment lasted for60days. The resultsshowed that the specific growth rates (SGR) decreased with the increase in stocking density under sufficient food supply. Meanwhile, oxygen consumption rates, ammoniaexcretion rates, digestive enzyme activities, pyruvate kinase and hexokinase activityalso decreased with the increase in stocking density. In high density treatments (4,6ind./40L), the SGRs and metabolic rate in isolated culture treatments were slightlyhigher than those in group culture treatments of the same density, but there were nosignificant differences. The present result proved that high stocking density producedstress effects on digestive enzymes activity and metabolic enzymes activity, whichadversely affect the growth of sea cucumbers. Physical isolation among individualscould significantly decreased individual growth variation in sea cucumber, but therewere no significant effects on the growth and physiological performance of seacucumber.3This study deals with the mechanism of social hierarchy affected individual growthvariation of sea cucumber. All cohort sea cucumbers were size-graded and thendivided into three groups, i.e. the big-size A. japonicus: the small-size A. japonicus1:3ind/40L (B); the middle-size A. japonicus: the small-size A. japonicus3:3ind/40L(M); the small-size A. japonicus: the small-size A. japonicus6:3ind/40L (S). GroupB, M and S were divided into three groups respectively according to different farmingmethods, i.e. group culture treatments (represented as B1, M1and S1, respectively),separated culture treatments (represented as B2, M2and S2, respectively) and isolatedculture treatments (represented as B3, M3and S3, respectively). Each treatment hadfour replicates and the experiment lasted for60days. The results showed that thespecific growth rates (SGR) of sea cucumber in group B1and M1were significantlylower than that in group S1while the coefficient of variations (CV) in group B1andM1were significantly higher than that in group S1. The SGRs of A. japonicus ingroup culture treatments were lower than that in separated culture treatments andisolated culture treatments while the CVs were higher than that in separated culturetreatments and isolated culture treatments. The present result proved that socialhierarchy was an important factor which affected the individual growth variation ofsea cucumber. Physical isolation among individuals would be effective to alleviate the “stress” effects of dominant individual to subdominant ones, and decreased individualgrowth variation.4The present study was conducted to investigate the effects of social hierarchy andphysical contact on the physiological performance of Apostichopus japonicus throughdetermining the activities of trypsin, amylase, lipase, pyruvate kinase (PK), hexokinase(HK), lactate dehydrogenase (LDH) and the content of lactic acid (LD) of seacucumbers in different treatments respectively. All cohort sea cucumbers weresize-graded and then divided into three groups, i.e. the big-size A. japonicus: thesmall-size A. japonicus1:3ind/40L (B); the middle-size A. japonicus: the small-size A.japonicus3:3ind/40L (M); the small-size A. japonicus: the small-size A. japonicus6:3ind/40L (S). Group B, M and S were divided into three groups respectively according todifferent farming methods, i.e. group culture treatments (represented as B1, M1and S1,respectively), separated culture treatments (represented as B2, M2and S2, respectively)and isolated culture treatments (represented as B3, M3and S3, respectively). Eachtreatment had four replicates and the experiment lasted for60days. The results showedthat the activities of digestive enzymes and metabolic enzymes of sea cucumbers ingroup B1and M1were significantly lower than that in group S1. The activities ofdigestive enzymes and metabolic enzymes of sea cucumbers in isolated culturetreatments were higher than that in separated culture treatments and group culturetreatments. The present result proved that social hierarchy adversely affected theactivities of digestive enzymes and metabolic enzymes of subordinate individuals of seacucumbers, while physical isolation among individuals would be effective to alleviatethe “stress” effects of dominant individuals to subdominant ones.5This paper studied the differences of cortisol level in coelomic fluid, energyallocation and biochemical composition between big-size and small-size seacucumbers (Apostichopus japonicus) in density treatments, and discussed the possiblemechanism of density stress affecting on individual growth variation. There were fivetreatments (stocking densities) of A. japonicus, i.e.2,4,8,16and32ind./40L glass aquarium (represented as D2, D4, D8, D16and D32, respectively) and each treatmenthad four replicates in this experiment. The experiment lasted for60days. The resultsshowed that stocking density have adverse effects on growth of the sea cucumbers inthe present experiment neither by water quality deterioration nor by food competition,but by the role of density as an environmental stress factor. The coefficient ofvariation (CV) of the animal body weight increased as the stocking density increased,and the CVs in D16and D32were over77%. The cortisol levels of small-sizeindividuals were significantly higher than those of big-size ones in every treatments.The density had no significant effects on cortisol levels of big-size individuals,however, the cortisol levels of small-size ones increased significantly with theincrease of the stocking density. The lactate level increased and glucose leveldecreased with the increase of the stocking density in general, but the lactate andglucose levels of small-size individuals changed more than those of big-size ones indominant position. This study proves that crowding stress can stimulate endocrinesystem of subdominant (small size) individuals raising cortisol level in coelomic fluid,in turn, accelerate energy consumption, modify energy budget model, and ultimatelyplay a negative role on the growth and biochemical composition of the subdominantindividuals.6This paper studied the differences of cortisol level in coelomic fluid, digestiveenzymes activity and metabolic enzymes activity between big-size and small-size seacucumbers (Apostichopus japonicus) in different treatments, and discussed thepossible mechanism of density and physical contact affecting on individual growthvariation. There were six treatments and each treatment had four replicates in thisexperiment. Treatment1,3,5were group culture treatments and stocking densitywere2,4,8ind./40L, respectively; Treatment2,4,6were isolated culture treatmentsand stocking density were2,4,8ind./40L, respectively. The experiment lasted for60days. The results showed that the specific growth rates (SGR) decreased with theincrease in stocking density, while the coefficient of variations (CV) in group culturetreatments increased. The density had no significant effects on cortisol levels of big-size individuals, however, the cortisol levels of small-size ones increasedsignificantly with the increase of the stocking density. The glucose level, digestiveenzymes activity, metabolic enzymes activity decreased and lactate level increasedwith the increase of the stocking density in general, but the enzymes activity, lactateand glucose levels of small-size individuals changed more than those of big-size onesin dominant position. The cortisol and lactate levels in isolated culture treatmentswere lower than those in group culture treatments of the same density, while theglucose level, digestive enzymes activity, metabolic enzymes activity were higherthan those in group culture treatments of the same density. This study proves that highdensity can stimulate endocrine system of subdominant (small-size) individualsraising cortisol level in coelomic fluid, in turn, accelerate energy consumption, inhibitnutrition absorption and energy intake, bring down the level of metabolic rate andultimately play a negative role on the growth of the subdominant individuals. Physicalisolation among individuals will be effective to alleviate the “stress” effects ofdominant individuals to subdominant ones, and decrease individual growth variation.7The present study deals with the effects of stocking density on the growth of seacucumber under limited food supply, Apostichopus japonicus. There were sixtreatments (stocking densities) of A. japonicus, i.e.2,4,8,12,16and20ind./40Lglass aquarium (represented as D2, D4, D8, D12, D16and D20, respectively) andeach treatment had four replicates in this experiment. The results showed thatstocking density. The results showed that the specific growth rates (SGR), the feedconversion efficiencies, the energy used for growth, the crude protein contents inbody wall decreased with the increase in stocking density, while the coefficient ofvariation (CV) of the animal body weight increased as the stocking density increased.After40days, the maximum value of biomass of big-size individuals was observed inD8. With the biomass of D8as a standard, the culture period extended in order whenthe biomass of D12, D16, D20, D4reached the standard, and the time was45,54,58,61days, respectively. At the end of the experiment, the biomass of big-sizeindividuals in D8was the maximum, and the biomass of big-size individuals were lower than initial biomass in D16and D20. Therefore, high stocking density candecrease the growth rate, increase individual growth variation, extend the cultureperiod reached for sale, and even decrease yield per unit (biomass). Low stockingdensity can effectively promote the growth and decrease individual growth variation,but the yield per unit may be at a low level. |
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