Reproductive biology of the notchedfin threadfin bream, Nemipterus peronii (Nemipteridae), in waters of southwestern Taiwan

Abstract

The notchedfin threadfin bream, Nemipterus peronii, is an important commercial species for the trawl fishery in Taiwan. Its reproductive biology is described, based on 1273 specimens collected between Nov. 1996 and Nov. 1997 by small trawlers in southwestern Taiwanese waters. The sex ratio, 0.59, significantly differed from 0.5 by X2 test, and females predominated when the fork length exceeded 100 mm. The combined-sex relationship between body weight (BW) and fork length (FL) was estimated as BW = 1.1 x 10-5 x FL3.096 (r2 = 0.948, n = 1213). Fecundity was estimated to range from 1.38 x 104 to 39.9 x 104. Oocytes were mature when they attained ≥ 0.5 mm in diameter. Batch fecundity was noticeably lower than fecundity, ranging from 688 to 192,437, while the relative fecundity ranged from 231 to 3981 (mean, 1487) per gram of BW. The logistic curves describing the relationship between the proportion of mature individuals (Pr) in each length interval and FL were estimated to be Pr = 1/(1 + e7.3027-0.0429FL) (r2 = 0.99, n = 351) for females and Pr = 1/(1 + e6.2165-0.0355FL) (r2 = 0.99, n = 258) for males. Sizes at 1st maturity were 96.7 and 104 mm FL for females and males, respectively. Size at 50% maturity was estimated to be 170 mm FL for females and 175 mm FL for males, corresponding to 1.72 and 1.64 yr old, respectively. The spawning season is prolonged, from Feb. to July, with a peak in Apr. to May. A seasonal closure from Apr. to May is recommended as a management measure for this species in southwestern Taiwanese waters.