Biological Studies On Breeding Of Two Color Variants Of Sea Cucumbers

The sea cucumber Apostichopus japonicus Selenka is an importantly commercial species in China, with good market value. In the present study, the culture biology of the green and red sea cucumber and the hybridization of the two color variants have been investigated. The main results are following:1 Effects of temperature and salinity on larval growth, survival and development of the green race, A. japonicusIn this study, two separate experiments were conducted to investigate the effects of temperature and salinity on survival and growth of Apostichopus japonicus larvae before and after feeding. 4 different levels of temperature (18, 21, 24 and 27°C) and 8 different levels of salinity (10, 15, 20, 25, 30, 35, 40 and 45‰) were investigated in A. japonicus larvae. The optimal temperature for both non-feeding and feeding larvae of sea cucumber was about 21 to 24°C. And the higher temperature (27°C) increased larval growth but reduced the survival in the culture. The production of normal early auricularia larvae from fertilized eggs were completed after 60 h at salinities of 20-35‰, but not at lower or higher salinity levels. And the best salinity was around 30‰for the normal development and transformation of A. japonicus larvae. The results obtained in this study demonstrate that water temperature of 21-24°C and salinity of 30‰were the most suitable conditions for the early development of A. japonicus.2 Effects of different substrates and environmental factors on larvae settlement in the green raceIn the present study, the effect of various substrata on the settlement of sea cucumber, A. japonicus, was evaluated. The settlement of the larvae in the experiments with three different substrata was compared and showed that polyethylene plastic sheet attracted significantly more larvae (P < 0.05) than plastic film and monofilament nylon. In addition, the highest setting rate was achieved for the plastic sheet with diatom-based films, followed by effective microorganisms (EM)-based films and natural microbial films, and the least recorded was on the plastic sheet without biofilms. There was a significant difference (P < 0.05) in the mean setting rates of the treatments, except between the diatom-based films and the EM-based films. Plastic sheets also appeared attractive to setting larvae when coated with tissue extracts of the same species. The number of settled larvae on substrates with tissue extracts was significantly greater (P < 0.05) than that on the control.Experiments were conducted to determine the effects of temperature, salinity and illumination on larval settlement of sea cucumber. The larvae were reared at four levels of temperature (18, 21, 24 and 27°C), four levels of salinity (20, 25, 30, and 35‰), and three levels of illumination (blue, green and black). The optimal temperature for larval settlement was 18-21°C, and the larval setting rate increased directly with temperature. However, when the temperature was over the optimal range (> 24°C), the larval setting rate was inversely related to temperature. There was a significant difference of larval settlement at different temperatures (P < 0.001). The optimal salinity for larval settlement was 30‰. The effects of higher or lower salinities on larval setting rate were significant (P < 0.001). There was a difference (P < 0.05) in the mean setting rates of the different levels of light. Larval settlement preference was associated with light avoidance behaviour, and the darkness was optimum for sea cucumber larval settlement.3 Effects of different nutritional additive on growth of the green race juvenileExperiments were conducted in culture tanks to investigate the effects of four different nutritional additive (Spirulina, Effective Microorganisms, Oligosaccharides, and Multivitamins) on juvenile A. janponicus. The results showed that the growth was significantly affected by spirulina, oligosaccharides and multivitamins, the weight growth rates of which were all higher than the control. There was no significant effect of EM on the growth of juvenile, compared to the control. The added level of EM needed advanced study. Additionally, the effects of different nutritional additives on the viscera body wall ratio of two-month old juveniles were not significantly different (0.13-0.15).4 Effects of stocking density, temperature and salinity on larval survival and growth of red A. japonicus The red race of the sea cucumber A. japonicus was introduced into China from Japan for large-scale seeding production because of its economical value. This paper reports the effects of stocking density, temperature and salinity on the survival and growth of early larvae before and after feeding, in order to establish the conditions for optimal larval growth. To maximize the yield per unit of space, densities of 0.5-1 larvae/ml is recommended for the non-feeding larvae, while 0.1-0.2 larvae/ml is appropriated for the feeding larvae. Higher survival and growth values were obtained for both the non-feeding and feeding larvae at temperature ranged from 21 to 24°C. And the larvae reared at salinity of 30‰always showed the maximum of growth and survival. Based on the results, a temperature from 21 to 24°C and a salinity of 30‰are optimum for the early development of the red A. japonicus.5 Salinity tolerance of red A. japonicus juvenile at different salinity and temperature levelsThe juveniles of red race sea cucumber acclimated in different environmental conditions (21, 24 and 27°C combined with 22, 27 and 32‰) were tested for salinity tolerance by increasing and decreasing salinity at a rate of 2‰. The results showed that the values of SSMax (Survial salinity maximum), SSMin (Survival salinity minimum), 50% CSMin (Critical salinity minimum) and 50% CSMax (Critical salinity maximum) all increased directly with salinity, but were inversely related to temperature. In the present study, an analysis of two-way ANOVA showed that salinity and temperature had a significant effect on survival of juveniles (P≤0.001).6 Microsatellite and AFLP analysis of the hybridization of sea cucumber Apostichopus japonicusThe hybrids between two colour variants of sea cucumber Apostichopus japonicus (the green♀×the red♂) were produced in this study, and the genetic relationship between the F1 progenies and their parents were examined using microsatellite and AFLP analyses. The results of microsatellite analysis confirmed that the F1 progenies were the hybrids between the two colour variants of sea cucumber. As a result of AFLP analysis, eight primer combinations generated 375 loci, among which 265 were polymorphic in F1 generation, accounting for 69.8%. Among the 238 segregating loci, 175 loci segregated in Mendelian model, including 69 maternal specific loci, 66 paternal specific loci and 40 mutual loci. Forty-one loci deviated from Mendelian ratios and 20 segregated in abnormal model. The genetic distance was 0.0391 between the F1 progenies and female parent, and 0.0999 between the F1 progenies and male parent, respectively, indicating that the hybrids were genetically closer to their maternal broodstock.