EFFECTS OF ENVIRONMENTAL FACTORS ON SEX DIFFERENTIATION ON LITOPENAEUS VANNAMEI

Effects of sex differentiation were studied by morphologic observation and continuous histological sections on L. vannamei at its early stage of growth on the temperature of (251)℃, (291)℃ and (331)℃, photoperiods (6L∶18D, 12L∶12D, 18L∶6D and 24L∶0D), light intensities (800 lx, 3000 lx and 5000 lx), salinity (10, 20, 30 and 40) and nonylpheno (NP, 40g/L, 80g/L and 120 g/L), respectively. Same brood of L. vannamei was selected and two repetitions were designed in order to induce the deviation. Level of temperature, light intensities, salinity and NP were adjusted by heater, salt, 55W lamp and nonylpheno, respectively. Ten samples were collected randomly in all the groups every 10 days till 70 days from the beginning of the experiment. Body and the second antenna length were measured, and morphology of the first and second pleopod were observed by using microscope. Meanwhile, samples in the 45d, 55d and 65d were fixed in the solution of Bouin, and embedded in paraffin and sectioned at 6-8 mm. Transverse sections were stained with haematoxylin and eosin, and histological sections were finished. At the end of the experiment (70d), all L. vannamei were collected for the statistics of the sex ratio. The data were analyzed by one-way ANOVA followed by Duncans multiple range tests. Results showed that temperature, photoperiods and light intensities had no influence on the female rate of L. vannamei (P0.05), while they had influence on the sex differentiating time; The ratio of female to male offspring were 0.81∶1, 0.67∶1, 1.29∶1 and 1.24∶1, respectively in salinity of 10, 20 and 40 group, as while as in environmental estrogen compound 4-nonylphenol (120 g/L) group, which deviated significantly from the ratio of 1∶1. Gonadal differentiating time could also be affected by salinity and 4-nonylphenol. In addition, the ratio of antenna to body length was in accordance with the sex differentiations time of both external morphology and gonad of L. van-namei, which suggested that the ratio of 1.0 could be used as an index for the onset of the sex differentiation on L. van-namei.