The Effects Of Temperature And Photoperiod Regulation On Reproduction Performance Of Cuttlefish Sepiella Japonica, Mollusca

Marine cephalopod, Sepiella japonica depending on artificial breeding and aquaculture development in recent years, it has become an ideal breeding species because of its fast growth and high feed conversion rate. But the study found that cultured Sepiella japonica generally showed precocious puberty. As the object of study, this article discussed how temperature and light influence precocious puberty and reproductive performance as well as other environmental factors.,which in order to explore the possible mechanism of precocious puberty. This article explored the regularity of oogenesis and gonadal development during all the reproductive cycle firstly. We overall cognized the changes of Sepiella japonica, s reproductive performance at different temperature and light using synthetically experimental ecology, histology, electron microscopy and radioimmunoassay(RIA) method, which provides reference and technical support for solving the problem of precocious puberty in culture conditions and establishing a stable Sepiella japonica healthy artificial breeding technology. The results of this study are as below.This study explored the relationship between the regularity of ovariansteroid hormone content changes and gonad cultured(ovarian development, oogenesis stages, gonad index, hepatosomatic index and fatness).On the basis of morphological changes characteristic of follicle cells and the oocyte, oogenesis may be divided into 7 stages: oogonia, primary oocytes, secondary oocytes and folding oocytes, full vitellogenic oocytes, late vitellogenic oocytes and ovulated oocytes; ovarian development could be divided into 7 stages. Sex steroid hormone content, gonad index, hepatosomatic index and fatness showed regular changes in the life cycle. In Ovarian developing process of phase IV~VII, there arehighly significant negative correlations between gonad index and hepatosomatic index(r=-0.835, P<0.01); there was a significant positive correlation of the variation of the content of estradiol and progesterone in ovarian(r=0.829, P<0.01).There may be a close responsive and transitive relation between the growth of Oocytes and the supply of hepatic energy.The study of temperature explored the changes of Sepiella japonica reproductive performance in the high temperature(29℃) and low temperature(23~24℃). The results showed that the effect of temperature on reproductive performance of Sepiella japonica was very significant(P<0.05). High temperature(29℃)group reached sexual maturity average21 days in advance than low temperature group. The results showed that estradiol and progesterone levels in low temperature group were significantly higher than those in the high temperature group(P<0.05) through detection of Sepiella japonica sex hormone levels in high and low temperature groups.The results show that the weight, fatness, body length, mantle length of male and female and liver somatic index of male was significantly lower than those inlow temperature group(P<0.05) through measuring physical size and growth index to Sexual maturity in high and low groups, which illustrates that the high temperature greatly shortened the time of maturity of Sepiella japonica, but greatly reduced the mature body size. This is typical of precocious puberty. So high temperature is an important factor to affect the precocious puberty of Sepiella japonica in culture conditions.In this study, the effect of photoperiod on the reproductive and growth performance of S.japonica had been tested for the first time. There photoperiods(23D:1L; 12D:12L; 1D:23L) were tested and the results showed that there was generally no obvious effect of photoperiod on the sexual maturation process of S. japonica. No obvious effect of photoperiod on the reproductive performance parameters, such as, spawning time, gonad size and gonad somatic index(GSI) of both sex, either. However, significant decrease of testis testosterone(T) and ovary estradiol(E2) were found in S. japonica of long light group(1D:23L) compared to that of other shorter light groups(12D: 12L; 23D: 1L). The growth performance was found to be affected significantly by photoperiod in S. japonica as well. But significant advantage was only found in the parameters of body weight, instantaneous growth rate and relative fatness of the female and body length of the male in the short light group(23D:1L) compared to that of the long light group(P<0.05). The results suggested that photoperiod control is not the main reason of causing precocious puberty, but we can considered how to prevent individual miniaturization.