Reproductive Biology of Thornfish Terapon jarbua from the Southwestern Waters off Taiwan

Abstract

Reproductive biology of the thornfish, Terapon jarbua was described based on 1,250 specimens caught by otter trawlers in the southwestern waters off Taiwan. These fish were purchased from fish markets at Tungkang and Linyuan from May 2002 to May 2003. Macroscopic appearance of the ovary, gonad somatic index, oocyte diameter frequency distribution and histological examination suggested that the spawning season of the thornfish in southwestern Taiwan waters runs from February to July. Eight stages of oocyte development were determined based on histological examination of ovary sections. Macroscopic observations of gonad showed five stages of ovarian development; immature, early maturing, late maturing, mature and spent and three testes stages. The sex ratio of 0.44 was not significantly different from 0.5 by using X^2 test, but the number of females was greater than that of males when fork length (FL) was greater than 180 mm. The males were dominant in the smaller size. The relationships between fecundity (F), batch fecundity (BF), and body weight (BW) were estimated to be F=-83.51+1.7365BW (r^2=0.73, n=131, P＜0.05) and BF=1.2586+0.0528BW (r^2=0.49, n=31, P＜0.05), respectively. Mean fecundity and mean batch fecundity (±SE) were estimated to be 143,596±88,338 and 1,016±576, respectively. Size at 50% maturity estimated by the logistic model were 159 mm FL and 163 mm FL for both females and males, respectively.