SHORT COMMUNICATION Effects of salinity and temperature on incubation period, hatching rate and morphogenesis of the red sea bream

The red sea bream, Pagrus major, which is widely distributed throughout the Far East, is the most important species of the family Sparidae for marine aquaculture in Japan (Ochiai and Tanaka, 1986). The total production of market-size red sea bream in Japan was over 72 000 tonnes (t) in 1993, with approximately 28% of the fish being derived from cultivation (Taya, 1995). In 1995 about 30 million red sea bream juveniles were produced: about 22 million being used for restocking into coastal waters, and the remainder were on-grown in commercial farms (Morita, 1997). In southern Japan, the natural spawning season starts at the end of February and lasts until early June, when water temperatures are within the range 15–23 °C (Higuchi, 1977). In captivity, the spawning season of the red sea bream starts in April and comes to an end in June (Harada, 1969; Kitajima, 1978). Although there are several reports, published mostly in Japan, on aspects related to red sea bream culture, relatively little is known about the environmental requirements of the early life stages of this species. Some effects of temperature and salinity on the embryonic development of red sea bream eggs were described by Matsuura and Kakuda (1980) and Yoo et al. (1991), while Apostolopoulos (1976) provided some information about the combined effects of these factors on the hatching of red sea bream eggs. The current study was undertaken to provide information about the effects of salinity and temperature combinations on the length of the incubation period, hatching rate and appearance of newly hatched larvae of the red sea bream. The experiments were carried out at the Fishery Research Laboratory of Kyushu University in 1994. Naturally spawned eggs were collected from a broodstock tank of 3 m3 water capacity during the spawning season (which in Kyushu is early April to June), washed carefully with fresh filtered seawater and transferred directly to the experimental room. Water temperature in the spawning tank during the experimental period ranged from 16.5 to 20.0 °C, and salinity corresponded to the normal salinity of water in the adjacent bay (29.0–32.5‰). Ten trials were conducted to test