Effect Of Diets, Temperature And Salinity On The Growth And Survival Of Sea Cucumber

The sea cucumber (Apostichopus japonicus) Selenka is an importantly commercial species in China because of its nutrition value and market value.Environmental factors can effect the growth and survival of the juveniles, so to explore the pattern of effect is important to the development of sea cucumber culture. The main results are following:1. Effects of marine yeast (Rhodomonas sp.) and four different microalgal diets on larval growth and survival at metamorphosis in the sea cucumber A. japonicusThe effects of the mixtures of marine yeast Rhodomonas sp. and four types of microalgae and the mixtures of two different microalgae on the growth and survival rate at metamorphosis in A.japonicus were examined. The growth and survival at metamorphosis were observed in the A.japonicus larvae fed on a combined diet of Rhodomonas sp. and four types of microalgae (Phaeodactylum tricornutum, Nitzschia closterium f. minutissima, Chaetoceros muelleri, and Isochrysis galbana) in the ratios of 1:0, 0.8:0.2, 0.6:0.4, 0.4:0.6, 0.2:0.8 and 0:1. The results indicate that when the microalgae were mixed with Rhodomonas sp. in appropriate ratio, the growth rate in body length of the larvae increased markedly. The survival at metamorphosis of the larvae fed on Rhodomonas sp. was obviously higher than those only fed on the microalgae. When two types of microalgae were mixed in the ratio of 1:1, the survival rate at metamorphosis of the larvae fed on the mixture of C. muelleri and N. closterium is clearly higher compared with those fed on the mixture of C. muelleri and I. galbana.2. Effect of temperature and salinity on temperature tolerance of the sea cucumber A.japonicusSea cucumber (A.japonicus) juveniles were examined for temperature tolerances at nine different environmental regimes (23, 25 and 27°C at 25, 30 and 35‰) by increasing temperature at a rate of 1°C h^-1. They were also tested for the LT₅₀ (median lethal temperature) when transferred directly into a series of higher temperature (27-33°C). The GLT₅₀ (LT₅₀ of gradual change of temperature) and ALT₅₀ (LT₅₀ of abrupt change of temperature) were increased directly with the acclimated temperature, but were inversely related to salinity. The GLT₅₀ of the juveniles that maintained at 27°C and 25‰was 35.9°C, and those maintained at 23°C and 35‰was 33.9°C°C. The ALT₅₀ of the juveniles that maintained at 27°C and 25‰was 30.1°C, and those maintained at 23°C and 35‰was 28.3°C°C.3. Effect of temperature and salinity on temperature tolerance of the juveniles that crossed by two color types of A.japonicusThe effects of temperature and salinity on temperature tolerance of the juveniles which were crossed by two color types of A.japonicus (Red and Green) were examined.The juveniles were acclimated in different environmental conditions (22, 25 and 28°C combined with 28, 33 and 38‰) for 3 weeks, then examined for temperature tolerance by two experiences: increased temperature at a rate of 1°C h^-1and transferred directly into a series of higher temperature. The CTMax (critical thermal maximum), STMax (survival thermal maximum), LT₅₀ (median lethal temperature) were positively correlated to the acclimated temperature, but negatively correlated to the acclimated salinity. When temperature increasing at a rate of 1°C h^-1, the STMax of the juveniles acclimated in the conditions of 28°C-28‰exhibited 34.9°C, higher than acclimated in the conditions of 22°C-38‰. When the juveniles were transferred directly into a series of higher temperature, the range of LT₅₀ is between 29.3°C and 31.3°C. Two-way ANOVA showed that temperature and salinity had a significant effect on the LT₅₀ (P<0.05).4. Effect of salinity and temperature on salinity tolerance of the juveniles that crossed by two color types of A.japonicusThe effects of temperature and salinity on salinity tolerance of the juveniles which were crossed by two color types of A.japonicus (Red and Green) were examined. The juveniles acclimated in different environmental conditions (24, 26 and 28°C combined with 27, 32 and 37‰) for 3 weeks, then examined for salinity tolerance by two experiences: increased or decreased salinity at a rate of 2‰h^-1 and transferred directly into a series of higher or lower salinity. The CSMax (critical salinity maximum), SSMax (survival salinity maximum), USTL (upper salinity tolerance limit) and LSTL (lower salinity tolerance limit) were positively correlated to the acclimated salinity, but negatively correlated to temperature. When salinity increasing or decreasing at a rate of 2‰h^-1, the SSMin-STMax of the juveniles acclimated in the conditions of 27‰-28℃were 15.0-33.0‰, but the SSMin-STMax of the juveniles acclimated in the conditions of 37‰-24℃were 23.0-46.0‰. When the juveniles were transferred directly into a series of higher or lower salinity, the range of LS50 is narrower than the LS50 when salinity increasing or decreasing at a rate of 2‰h^-1. Two-way ANOVA showed that temperature and salinity had a significant effect on 50% CSMax,50% CSMin,USTL and LSTL (P<0.05).