Fish Physiology and Biochemistry 28: 445–446, 2003. © 2004 Kluwer Academic Publishers. Printed in the Netherlands.
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Effects of temperature on gonadal development of mudskipper (Periophthalmus modestus) T. Shiota1 , A. Ishimatsu1 and K. Soyano1,∗ 1 Marine
Research Institute, Nagasaki University, Nagasaki 851-2213, Japan; (Fax: +81-95-840-1881; E-mail:
[email protected])
∗ Author
for correspondence
Abstract The effects of different temperature on gonadal development of Periophthalmus modestus were examined by histological and endocrinological analyses. Results showed that vitellogenesis and spermatogenesis were induced by high temperature treatment (30 ◦ C). While, gonadal development did not occur in the low temperature treatment (18 ◦ C). These results suggest that a rise in temperature plays an important role in gonadal development of this fish. Introduction Periophthalmus modestus is a common mudskipper which inhabits tidal flats in Japan. Its number has been decreasing dramatically with the reduction of tidal flats. This fish plays a key role in the ecosystem of tidal flats. However, little information is known about the reproduction of this fish. In our previous study, the increase in gonadsomatic index (GSI), and initiation of vitellogenesis and spermatogenesis were observed in spring, when temperature increased rapidly. The result showed the possibility that a rise in temperature affects gonadal development and maturation in this fish. In the present study, we exposed pre-vitellogenic and pre-spermatogenic fish to two temperature regimes to examine the effects of temperature on gonadal development.
were measured by ELISA. In addition, wild fish were also examined, similarly.
Results In the high temperature group (30 ◦ C), GSI significantly increased on day 52, and reached maximum levels on day 78. In this group, initiation of vitellogenesis was confirmed on day 52, and spermatogenesis started on day 26. Plasma vitellogenin concentrations increased on day 52. In contrast, in the low temperature group (18 ◦ C), vitellogenesis was not observed. Although spermatogenesis started, sperm production was not induced. In the wild fish, the increase in GSI in males and vitellogenesis in females started on day 78, when the environmental temperature was above 20 ◦ C.
Materials and methods
Discussion
Pre-vitellogenic and pre-spermatogenic fish were collected from the Ariake Sound in early February. They were divided into two temperature groups (18 and 30 ◦ C), and were reared under a long photoperiod (14L-10D). Gonads and blood samples were obtained from each group every 26 days from early February to late April. GSI was calculated, and histological observation was done. Plasma vitellogenin concentrations
In the high temperature treatment (30 ◦ C), GSI and plasma vitellogenin concentrations significantly increased, and vitellogenesis and sperm production started during the experimental period. In contrast, in the low temperature treatment (18 ◦ C), GSI or plasma vitellogenin concentrations did not increase. Likewise, vitellogenesis or sperm production did not start. In the wild fish, the increase in GSI and vitellogenesis started
446 in late April, when the environmental temperature was above 20 ◦ C. These results suggest that the gonadal development of Periophthalmus modestus is induced by a rise in temperature, and the effective temperature for inducing gonadal development is about 20 ◦ C. In the low temperature treatment (18 ◦ C), spermatogenesis started, however, vitellogenesis did not occur. The effective temperature for males may be slightly different from that of females. In this experiment, both high and low temperature group were kept at the same photoperiod (14L-10D). There have been many studies on the effects of photoperiod on gonadal development and
maturation in teleosts (Okuzawa et al. 1989). In the future, it is necessary to investigate the effects of both photoperiod and temperature on gonadal development of this fish.
References Okuzawa, K., Furukawa, K., Aida, K. and Hanyu, I. 1989. Effects of photoperiod and temperature on gonadal maturation, and plasma steroid and gonadotropin levels in a Cyprinid fish, the Honmoroko Gnathopogon caerulescens. Gen. Comp. Endocrinol. 75: 139–147.
