Cutlassfish, Trichiurus lepturus Linnaeus 1758, is found throughout tropical and temperate waters of the world. About 80% of the world production are landed by China and it is also the most important commercial marine fish species of China in terms of weight. Cutlassfish is caught from all Chinese waters, from the Bo Hai, the Yellow Sea, and the East China Sea to the South China Sea. Many studies have been done to reveal the age, growth and reproduction of T. lepturus, however, no study has been conducted on the South China Sea's population(s). Furthermore, recent studies had shown that in the South China Sea there are three species - T. lepturus, T. nanhaiensis and T. brevis - instead of one - T. lepturus - as in the northern seas of China. The aim of this study is to investigate the g...[ Read more ]

Cutlassfish, Trichiurus lepturus Linnaeus 1758, is found throughout tropical and temperate waters of the world. About 80% of the world production are landed by China and it is also the most important commercial marine fish species of China in terms of weight. Cutlassfish is caught from all Chinese waters, from the Bo Hai, the Yellow Sea, and the East China Sea to the South China Sea. Many studies have been done to reveal the age, growth and reproduction of T. lepturus, however, no study has been conducted on the South China Sea's population(s). Furthermore, recent studies had shown that in the South China Sea there are three species - T. lepturus, T. nanhaiensis and T. brevis - instead of one - T. lepturus - as in the northern seas of China. The aim of this study is to investigate the growth and reproduction of the cutlassfishes from the South China Sea. In a 12-month (Dec. 1996 to Nov. 1997) sampling period, 1495 specimens were collected from Hong Kong coastal waters of which two species - T. lepturus, T. nanhaiensis - were identified.

Ages were estimated using sagittal otolith transverse sections and opaque growth rings were validated to have formed once per year during February. Preanal length (PL) and age (t) were fitted with the von Bertalanffy growth model by non-linear regression, resulting in:

PL (mm) = 589{ 1 - e^{[-0.168(t+2.682)]}} (T. lepturus);

PL (mm) = 602{ 1 - e^{[-0.207(t+2.044)]}} (T. nanhaiensis ).

The growth curves of the two species were significantly different (ANCOVA, F_2,1245=78.81, P<0.001). Otolith weight showed a linear relationship with the age, which accounted for about 72% and 76% of the variation in age for T. lepturus and T. nanhaiensis respectively, comparable with the von Bertalanffy growth models in preanal length. Otolith weight provided a more precise estimate of age than preanal length for older fish.

Spawning period and reproductive cycle were studied by checking the temporal profile of Relative Gonadal Index/Gonosomatic Index and by examining the ovaries macroscopically and whole oocytes microscopically. All three methods provided similar results: the spawning period of T. lepturus and T. nanhaiensis were March to June and April to August respectively. The mean preanal length at sexual maturity of T. lepturus and T. nanhaiensis females were 255 mm and 282 mm respectively. The sex ratios of both species were proven to be significantly different from 1: 1 among different sampling months, different ages and size ranges.