Biological study of red snapper, Lutjanus sanguineus

Among the red snappers caught by trawling in the South China Sea, L. sanguineus is the most important species, comprising more than 10% of the total catch. Although L. sanguineus is widely distributed in the South China Sea, its pattern of distribution seems to be rather patchy. However, they were most abundant at 35—80 m. water depth and inhabit muddy-sand areas especially where “Neptune’s cup” are abundant. Size frequency histograms indicate four to six size groups, with peaks of almost the same height. The growth rate of fish of 23 cm. was taken to be approximately 2 cm. per month. As no significant difference in length-weight relationship between male an female was observed, the following formula can be applied for both sexes. W = 7.64 x 10–5 L2.823 where, W = body weight (g). L = body length (mm). The number of ovarian eggs ranged from 69 to 260.104 and the regression between the number of eggs in thousand (N) and fish weight in gram (W) was N =0.4459W + 83.2. High values of gonadal index from March to November with a peak in April—June suggests a prolonged spawning season.