| In order to cultivate a new salinity tolerance breed of tilapia, the Oreochromis niloticus ♀×Sarotherodon melanotheron♂ hybrids with fast growth and high salinity tolerance was obtained through the artificial interspecific hybridization method by Shanghai Ocean University. But it belongs to the distant hybridization, can’t reproduce naturally, and the asynchronous spawning habits of tilapia, resulting in hybridization process is difficult to obtain mature eggs for artificial insemination, the new varieties of large-scale production is difficultly. Therefore, the morphological characteristics of breeding O. niloticus eggs, S. melanotheron sperms and motility under different environmental factors of sperms; changes of sex steroid hormone, vitellogenin content and Vtg m RNA expression during ovarian maturation of O. niloticus were studied so as to provide some basic data to improve the tilapia breeding of new varieties and artificial hybridization techniques.During the breeding season, eggs of female O. niloticus and sperms of male S. melanotheron were collected by abdominal squeezing of the brood stocks. The eggs shape, size, color and accumulation of yolk granules at different matured stage were analyzed by optical and anatomical microscope techniques, the result showed that the immatured eggs were oval-shaped and covered with small blood vessel; the matured eggs were pear-shaped, eggs diameter were 0.5~1.6mm, they were coated with a transparent egg membrane and filled with large amounts of golden yellow yolk granules; the over-matured eggs were irregular shapes, with some liquefied yolk granules. The sperms were observed by scanning electron microscopy technique, normal sperms were composed with head, middle and tail piece, the head was an elongated cone, long diameter was 1.82 ± 0.35μm, wide diameter was 1.41 ± 0.34μm; the middle piece was short and approximately cylindrical, long diameter was 0.74 ± 0.08μm, wide diameter was 0.16 ± 0.06μm; the tail, single flagellum structured, was extremely long 16.42 ± 0.35μm. Three types of abnormal sperm including short-tailed, double headed, and two-tailed, were also observed.The sperms fast moving time, total duration and activation rate under different condition were recorded by microscopy observation. The result showed that the activation rate was highest over 90% when p H ranged from 7.5~8.0, fast moving time and duration reached longest in p H 7.5, respectively for 66.33±2.25 s, 933.17±25.79 s. The activation rate of sperms were over 80% when salinity ranged from 25‰~32‰, fast moving time and duration reached longest at 30‰ salinity for 63.50±2.35 s, 402.50±7.31 s, respectively. The activation rate and motility of sperms increased with the increasing of K+ concentration, when it was 75mmol/L, the motility reached highest, then decreased sharply. Ca2+ inhibited the sperm motility and caused their aggregation, the activation rate and motility were highest just 37.8mmol/L, then with the increasing of Ca2+ concentration, this effect was enhanced. Compared with K+, Ca2+, glucose could effectively extend the duration of sperms, it kept 281.00 ± 5.90 s when the concentration reached 150mmol/L, the activation rate could over 80% under 125mmol/L.The changes of sex steroid hormone(estradiol E2, progesterone P), vitellogenin content and Vtg m RNA expression during ovarian maturation of O. niloticus were studied by histological, ELISA and q RT-RCR techniques, respectively. The result showed that gonadosomatic index(GSI) of O. niloticus was consistent change with ovarian development, and reached a peak at stage Ⅴ. The levels of E2 in the serum increased significantly since stage Ⅱ, reached a peak at stage Ⅳ, then decreased significantly at stage Ⅴ; whereas the levels of P increased gradually since stage Ⅱ, reached a peak at stage Ⅴ, then decreased significantly at stage Ⅵ, E2 and P played different role at the early and late ovarian development stage, respectively. The Vtg content in the liver increased first, then decreased, and reached a peak at stage Ⅳ; the content of Vtg in the serum and ovary increased gradually since stage Ⅱ, reached the peak at stage Ⅴ, then decreased significantly at stage Ⅵ. The expression of Vtg m RNA in the liver reached a peak at stage Ⅲ, then decreased gradually since stage Ⅳ; while the expression level in the ovary was relatively lower, and reached a peak at stage Ⅴ. It suggested both liver and ovary were involved in Vtg synthesis, liver was the major synthesis organ, mostly active during the yolk accumulation phase, while Vtg synthesis in ovary was relatively low. |
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