Determination of the spawning time and changes in the reproduction cycle of ribbon fish, Trichiurus lepturus, according to the hepatosomatic index and gonadosomatic index

The ribbon fishes, belonging to the family Trichiuridae, are one of the most important protein resources in the Indian Ocean. A considerable density of the dominant species of this family, Trichiurus lepturus has been observed in the Oman Sea. During the conducted cruises in the northern part of the Oman Sea, gonadosomatic index (GSI) and hepatosomatic index (HSI) were estimated according to the size of the female groups of Trichiurus lepturus. GSI increases significantly from September to next April (P <0.05). polymodal egg size frequency revealed prolong spawning time by the females. The HSI fluctuations are good indications for this type of reproductive behavior

Sex hormones changes in the reproductive cycle of female Trichiurus lepturus

Ribbon fish, family Trichiuridae, is one the most important protein resources of the Indian Ocean. The considerable density of these aquatic animals, especially the dominant species Trichiurus lepturus, has drawn many researchers' attention to its biological characteristics and its reproductive characteristics in particular. The sampling was carried out in the Oman Sea from March 95 to November 96 (n=778). Studies on Estradiol - 17 - β, Progesterone and Cortisol hormones in female Trichiurus lepturus indicated that the production of these hormones increases considerably from maturity stage II. The serum levels of Estradiol - 17 - β hormone peaked during September, October and November and it remained high in the other months (1500 pg/ml). High levels of Progesterone occurred from December to March (during the spawning season). The changes in the Cortisol levels from August to December and again from February to March (0.5 - 3.5 mic/100 ml) were significant. The Estradiol - 17 - β fluctuation was observed simultaneously with the vitellogenesis process and absorption of Vitelline by the oocytes during their maturation. The changes in the oocytes membrane as well as the perforated channels impact on serum levels of Estradiol - 17 - β and Cortisol hormones have been discussed in this paper. The relative high levels of Estradiol - 17 - β during the whole year is probably related to the long spawning season of this species during autumn, winter and spring