Abstract: Based on elongata poatholefish Gonostoma elongatum samples collected by middle water trawl in the central- southern part of the South China Sea during 2013 and 2014, body length and body weight composition, age and growth, gonad maturity composition, feeding stage of G. elongatum were studied. The results are as flows. At 150 m depth, the range of body length is 80~128 mm, and the dominant size is 80~100 mm that is 84.2% of the total. At 200 m water layer, the range of body length is 43~195 mm, and the dominant size is 80~140 mm that is 76.9% of the total. At 400 m water layer, the range of body length is 86~186 mm, and the dominant size is not obvious. The mean size of G. elongatum has an increasing tendency from shallow to deep water, first increasing and then decreasing tendency from south to north. T-test indicates that the body length distribution at 150, 200 and 400 m presented significant differences (p<0.01). In spring, the mean body length and mean weight were 111 mm and 3.84 g, respectively. In autumn, the mean body length and mean weight were 140 mm and 5.50 g, respectively. In winter, the mean body length and mean weight were 134 mm and 7.44 g, respectively. The growing parameter, b value, is 3.0726, which indicates isometric growth in G. elongatum. A total of 45 statoliths of G. elongatum were identified, including 35 individual of one year old and 10 individual 1⁺ years old. The minimum age was six months old with mean body length of 128 mm; the maximum age was 16 months old with body length of 187 mm. The mean body length and mean body weight of fish of one year old were 138 mm and 5.12 g, respectively. The mean body length and mean body weight of fish of 1⁺ year old were 157 mm and 7.53 g, respectively. The gonad maturity of G. elongatum is mainly at stagesⅠand Ⅱ, and the highest stage appears in spring. The feeding stage of G. elongatum is mainly at stages 0 and 1, and the highest feeding stage is 3. On the whole, the feeding stage of G. elongatum is not much different at these depths.

Key words: South China Sea, mesopelagic fish, Gonostoma elongatum, fishery biology, age, growth