Biology Of Triploid Chinese Shrimp, Fenneropenaeus Chinensis

Triploid Chinese shrimp, Fenneropenaeus chinensis,were induced by heat shock to inhibit meiosisⅠor meiosisⅡin the present study. The differences in metamorphic survival rate , acclimation ability to environmental factors, growth behaviors, hematological character encountered pathogens, activities of several immunity oriented enzymes, and energy budget between sibling triploid and diploid F. chinensis were compared. This study aimed at offering basic biological information and theoretical evidences for the application of triploid F. chinensis. The effects of heat shock treatment on metamorphic survival rate in induced triploid populations and untreated diploid populations of F. chinensis were determined. Triploid rate in four populations of heat shock treated shrimp were assayed, and metamorphic survival rate of their early stages from zoea to postlarvae in diploid and triploid shrimp were calculated. It showed that, heat shock dramatically lowered metamorphic survival rate of their early stages from zoea to postlarvae after hot shock treatment, but there was no remarkably effect of ploidy on shrimp metamorphic survival rate. Triploid rate in shrimp populations exhibited a fluctuant reduced tendency in their early stages, but in their juvenile stage or later, triploid rate tended to a relative stabilization, there was no significant difference in survival between diploid and triploid shrimp during their later culture. The effects of salinity on survival, growth, and molt in full-sib diploid and triploid F. chinensis were determined. In condition of abrupt salinity change, survival was not affected by salinities from 10 to 40ppt during the 96h exposure periods in all the three types of shrimps, but noticeably affected by lower (<5ppt) or higher salinity(>50ppt). There was no significant difference (P>0.05) in tolerance to abrupt salinity changes in triploid shrimps from that of diploid ones. Lethal salinity for 50% of the individuals in 96h (LS50, 96h) at 23-25℃ was about 2ppt. During the 28-days culture with previous acclimatization, all the three types of shrimps reared in 10ppt suffered lower survival, growth rate and longer intermolt period. Diploid shrimp at 20ppt grew faster than those at 10 and 30ppt, compared to triploid shrimp with 30ppt. The intermolt period of all the three types of shrimp shortened as elevated salinity. MeiosisⅠtriploid shrimps grew slightly faster than Meiosis Ⅱ triploid ones in all the three salinity levels, whereas no significant difference (P>0.05). Based on the survival and best growth results, the salinity optima for the culture of triploid F. chinensis was 20-30ppt or above. Temperature diffusely affected shrimp growth, survival, feeding, and molt. During the experiment-designed temperament range from 26 to 32℃, growth rate increasing with the temperature in both diploid F. chinensis and 3n-ⅡF. chinensis, but for 3n-Ⅰshrimps, it seems grow faster at 29℃. 3n-ⅡF. chinensis grows faster than diploid shrimps and 3n-Ⅰshrimps in higher temperature (29 and 32℃). As the temperature increasing, the feeding rate (FR) in all the three types of shrimp increased, but the feed conversion ratio (FCR) and survival decreased accordingly. High temperature (32℃) dramatically prolonged the intermolt period (IP) of diploid F. chinensis, whereas the ecdysis of meiosisⅡ triploid F. chinensis seems no sensitivity to temperature. The optimal temperature for the culture in both diploid and triploid F. chinensis was 29℃. Hematological changes of sibling diploid and triploid F. chinensis after being challenged with pathogens were compared. Triploid (3n-Ⅱ) shrimps and their diploid siblings were challenged with White Spot Syndrome Virus (WSSV) through oral administration or with Vibrio anguillarum by injection. Hemocyte density and composition in hemolymph of diploid and triploid shrimp were compared. This is the first time to report the hemocyte density and composition of hemolymph in triploid shrimp. A significantly decline for hemocyte density in both diploid and triploid shrimp after 4 days challenge was observed. Hemocyte density of both diploid and triploid shrimp reduced to about 10% of that of control. The composition of hemocytes either in diploid or triploid shrimp changed after WSSV challenge. The amount of large granule cells (LGC) decreased, while that of small granule cells (SGC) increased. However, the amount of hyaline cells (HC) remained unchanged. Some abnormal structures such as vacant vacuoles were found in SGC and LGC of the challenged shrimps. Hemocyte count of diploid and triploid shrimp decreased alsoafter being infected with V. anguillarum, and the range of decline was positively related with the injection dosage of V. anguillarum. The hemocyte composition in triploid was the same as that in diploid, and the total cell counts in hemolymph in triploid shrimp accounts for about 40% of that of diploid. The activities of several immunity-oriented enzymes in shrimp serum of F. chinensis originated from different ploidy operations were measured. It showed that, all the three activities of antibacterial, lysozyme, and superoxide dismutase in both two types of triploid shrimps and diploid shrimps detected out from triploid induced populations were higher than diploid (control) shrimps without heat shock treating, but the phenoloxidase activities in diploid shrimp serum of F. chinensis was the highest. Results above provide basis and reference for stress resistance research on triploid shrimp. There was no significant effect (P>0.05) of ploidy manipulation on energy budget of F. chinensis in their initial stage of gonad development, but both the meiosis Ⅰtriploid and meiosis Ⅱ triploid F. chinensis exhibited higher net growth efficiency and assimilation efficiency than their diploid control. The equations of energy allocation in diploid and triploid Chinese shrimp, F. chinensis were listed as below: 2n:100C=17.35G+7.88F+2.16E+66.18R+6.39U 3n-Ⅰ:100C=17.69G+7.11F+2.19E+71.85R+7.50U 3n-Ⅱ:100C=18.71G+7.18F+2.39E+65.64R+6.07U.