Reproductive Biology of Lizard Fish, Saurida tumbil (Forskal) in the Jizan Region of the Red Sea

The reproductive biology of lizard fish Saurida tumbil in the Jizan region of the Red Sea was studied during 1986. Females outnumbered males and attained larger size than males. Among young individuals male s were more numerous than females, while in older age groups the females were more num erous. There is no significant difference in length-weight relation ship between the sexes . The equa tion for the two sexes are found to be log w = log 1.954 + 2.958 log L Th e sma llest size at first maturity was 11cm for males and 13 cm for females. About 50% of the fem ales were mature at a length of 19 cm. Th e spawning of males and femal es extended throughout the year. The greatest amount of spawning was observed during winter . Gonado-carcass ratio of fem ales was high from October to May . Spawning is often concentrated at the time of the year when prevailing winds or current s are at their weakest. Monthly vari ations in the visceral carcass ratio and relative condition were analysed for both sexe s in relation to spawning activity. Thi s species is carnivorous and feeds mainly on fish . Introduction The spawning time and its relation to environmental factors in tropical fish have been reviewed by many authors (Munro et al., 1973; Erdman, 1976; Johannes, 1978; Fursa, 1979). There are various methods to measure the spawning time of fish, one of which involves estimation by the frequency of occurrence of the eggs and larvae of fish in the sea whilst the other is based on frequency of ripe fish in the catch (Fursa, 1979). Some work has been carried out on the various aspects of the biology of S. tumbil. In the Indian waters Rao (1984) studied the length-weight relationship. However, Budnichenko and Nor (1978) and Budnichenko and Dimitrova (1980) described growth and reproductive biology of the S. tumbil in the Arabian sea . Recently, Euzen (1989) and Mathews and Samuel (1989) studied the feeding habitats and population dynamics of the same species in Kuwait waters. During an earlier study in the Jizan area, the lizard fish Saurida tumbil (Forskal) was found to be one of the most regularly occurring and abundant species throughout the year (Oakley and Bakhsh, 1989). In spite of these studies, similar work in the Red Sea is 169 lacking. Therefore, the aim of this paper is to provide some basic information on the reproduction of lizard fish close to Jizan and Farasan Island . The various aspects covered include sex-ratio, length-weight relationship, length at first maturity, spawning pattern. Material and Methods Biological studies were carried out on lizard fish, . Saurida tumbil, from the coastal waters of Jizan, southern Red Sea . Fish samples were collected during 1986 by experimental trawl fishing with mesh size of 60-70 mm and from commercial fishing trawlers (40-50 mm) of the Saudi Arabia Fisheries Company (SFC). Details of the hauls made and the area trawled are given in Oakley and Bakhsh (1988, 1989). In the laboratory, total length and carcass weight (i.e. total weight less gonad, viscera and food content) were measured . Monthly fluctuations in the gonad/ carcass ratio (OCR) for both sexes were estimated. The OCR was calculated as follows: GCR = [gonad weight]/[carcass weight] x 100 The visceral/carcass ratio (VCR) was calculated in