Aquaculture and Fisheries Management 1991, 22, 317-321 Effect of temperature on the hatching success of the eggs of Japanese whiting, Sillago japonica Temminck & Schlegel, during the spawning season M. S. KHAN, M. S. ZAKARIA, M. A. AMBAK, M. J. ALAM*, M. KASHIWAGI** & T. IV^AVFaculty of Fisheries and Marine Science, Agriculture University of Malaysia, Serdang, Selangor, Malaysia Abstract. Hatching responses of the Japanese whiting, Siiiago japonica Temminck et Schlegel, to a series of temperature changes were measured by exposing the fertilized eggs to eight constant incubation temperatures which ranged from 20-0 to 34-0°C. For a control, hatching temperature was kept the same as temperature of the ambient environment. Hatching responses were expressed as hatching percentages. Altogether 18 experimental trials were conducted during the natural spawning season of the species which extended over a period of 2 months from late July to mid-September 1988, when seawater temperature varied between 24-0 and 30-0°C. Optimum and limiting temperatures were recorded and the data were optimally fit to the quadratic model. Results indicated that viable hatch occurred at almost all ranges of hatching temperature from 22-0 to 32-0°C. However, no hatching was recorded at either 20-0 or 32-0°C. The experiment showed that the optimum hatching temperature varied with the ambient temperature changes during the spawning season, indicating the latter to be a dependent factor for any hatching success. Introduction Temperature and salinity have major effects on development of eggs at fertilization (Blaxter 1969; Alderdice 1972). With various other environmental factors, temperature largely determines the rate of hatching success, as it acts directly on organogenesis. The effect of temperature on hatching success is greater than that of salinity (Blaxter 1969; Holliday 1969). In aquaculture, successful production depends to a large extent on the rate of survival of the embryo in its post-fertilization development. Japanese whiting, Sillago japonica Temminck & Schlegel, is a widely distributed species in the waters off Japan, Taiwan and the Philippines and is an important catch for food and recreational fisheries in Japan. Limits of tolerance of temperature and chlorinity on the hatching success of the eggs of tropical and temperature species have been reported elsewhere (Alderdice & Velsen 1971; Lopes, Kashiwagi & Iwai 1985; Kashiwagi, Iwai, Yamamoto & Sokabe 1986). There have been several studies on the effects of both temperature and salinity on egg size and hatching rate of the Japanese whiting (Kumai & Nakamura 1978; Lee 1981; Kashiwagi, Yamada, Okada & Nakamura 1984; Oozeki & Hirano 1985). Kashiwagi etal. (1984) reported periodic variation of spawning of 5. japonica during the spawning season. Lee (1981) described various factors affecting egg characteristics in 5. sihama. Oozeki & Hirano (1985) studied the effects of high temperature tolerance limits in 5. japonica. They exposed fertilized eggs to Correspondence: M. S. Khan, Faculty of Fisheries, 43400, UPM, Serdang, Selangor, Malaysia. • Presen t address: Fisheries Research Institute, Mymensingh 2201, Bangladesh. "Present address: Faculty of Fisheries, Mie University, Japan.