| Sex differentiation on crustacean was determined by genes, however, it was easily affected by some environmental factors, such as temperature, photoperiod and parasite, etc. There exists obviously different body size between male and female in many economical crustaceans, especially in shrimp. If those sexy superior characteristics can be applied well in aquaculture, the breed benefit would be improved greatly. Body size of female Litopenaeus vannamei is larger than that of fale. Hence, if a good work can be done in feminizating of L. vannamei, the shrimp production and the economic benefit would be increased drastically. Effects of temperature, light, salinity and nonylphenol on sex differentiation were studied by morphologic observation and continuous histological sections on juvenile L. vannamei at its early stage of growth. The primary results of these studies are listed below:1. Effects of temperature on the sex differentiation on L. vannamei:Effects of different temperatures (25±1℃, 29±1℃and 33±1℃) on sex differentiation were studied at the early stage of growth on L. vannamei. The female rate was calculated following the experiment. The results showed that temperature obviously influenced the growth, sex differentiation starting time and survival rate of L. vannamei, but there were no significantly difference of female rate among the shrimps under the three temperature treatments (P﹥0.05). Sex differentiating time of both gonad and external morphology on L. vannamei at 29±1℃and 33±1℃groups were earlier than that at the 25±1℃group, so were the mean body-length. What's more, the survival rate at 29±1℃(31.4±3.1%) was significantly higher than that at other groups.2. Effects of light on the sex differentiation on L. vannamei:Effects of different photoperiods (6L:18D, 12L:12D, 18L:6D and 24L:0D) and different light intensities (800lx, 3000lx and 5000lx) on the sex differentiation were studied at the early stage of growth on L. vannamei. The female rate generally raised with the illumination time from 6L:18D to 18L:6D, and the highest female rate (57.5±1.4%) existed at the 18L:6D group. The female rate at the 800lx group was higher than that at the other groups. However, it was not affected significantly by the changes of photoperiod and light intensity on L. vannamei (P > 0.05). The earliest sex differentiations time of both external morphology and gonad, as well as the largest mean length was found at the 18L:6D and 800lx group. The highest survival rate (28.5±4.9%) was found at the 24L:0D group, which was significantly higher than that at the 6L:18D group (P﹤0.05). However, no significant difference (P﹥0.05) in survival rate was found among the light intensity groups.3. Effects of salinity on the sex differentiation on L. vannamei:Effects of different salinity levels (10, 20, 30 and 40) on the sex differentiation were examined at the early stage of growth on L. vannamei. The results showed that female rate (58.2±7.7%) at the salinity 40 group was significantly higher than that both at the 10 and 20 salinity groups (P﹤0.05), however, no significant difference in female rate was observed between the salinity 30 group and the other three groups (P﹥0.05). The female rate increased and the survival rate decreased with the increasing salinity from 20 to 40. The lowest survival rate was found in salinity 10 group, which was significantly lower (P﹤0.05) than that at salinity 20 and 30 groups. Moreover, the sex differentiations of external morphology and gonad at salinity 10 were later than that at the other three salinity groups.4. Effects of nonylphenol on the sex differentiation on L. vannamei:Effects of environmental estrogen compound—4-nonylphenol (NP, 0μg/L, 40μg/L, 80μg/L and 120μg/L) on the sex differentiation were examined at the early stage of growth on L. vannamei. The results showed that the sex ratio (female: male) was up to 1.24:1 at the 120μg/L NP group, which was significantly higher than that both at the control (1:1.01) and the 80μg/L NP group (P﹤0.05). The sex differentiations time of both external morphology and gonad at the 80μg/L and 120μg/L NP group were earlier than that at the control and the 40μg/L NP group. There were no significant differences (P﹥0.05) in survival rate between the control and the three NP groups.
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