Altogether 2866 specimens of male Trichiurus haumela were collected using bottom trawlers in the northern East China Sea (20°30′ to 31°30′N) during 1979 to l980. The samples were frozen on board and taken back to the laboratory for examination. The standard length (i.e. the distance from the tip of lower jaw to the anterior margin of anus) and weight (excluding guts and gonads) were recorded for all specimens. For all of the specimens collected, the testis were examined in order to determine their stage of sexual development. 59 of total testes at various stages of maturity were sectioned and stained with haematoxylin and eosin for histological examination. Description of the stages of maturity of males was based on histological and macroscopical characters (Tab.1 and Plate I).
The size at the first maturity of male hairtails was observed. The smallest mature male was 130 to 140 mm in standard length and 20 to 40 grams in weight, for both the spring-summer brood or the autumn brood. All males attain sexual maturity when they exceed l80 mm in standard length and 100 grams in weight (Tab.2).
The age at the first maturity and the course of maturation of the two-year classes for male were studied. Individuals of the early brood (i.e. spring brood of the current year) can reach maturity in July, i.e., 4 to 6 months after hatching. For individuals of the late (autumn) brood, it takes 8 to 10 months after hatching to attain maturity in May. Generally, all individuals hatched at different seasons of the same year will be sexually mature when they are one full year old in the subsequent year. Maturation is completed in the course of one year (Tab. 3).
Because of the difference in brood seasons, the peak of first spawning of the hairtail varies. Based upon an analysis of the seasonal fluctuation of GSI (gonado-somatic index) for the male fish, spawning of the early brood group for l year-old occurs in June and July, whilst that of the late brood group occurs in July to September Fig.1. Therefore, the first upsurge of spawning is closely related to the seasons of brood of hairtail. The spawning upsurge after the third year (2-year-old) is not related to seasons of brood. The spawning upsurge of both broods occurs in May and June. |