Gonad analysis of Antarctic toothfish in Subareas 58.4 and 88.3

The ratio of female among the 600 specimens of Antarctic toothfish collected from the 58.4.1 area and 88.3 area within the CCAMLR Conservation Zone during February through March, 2013 was found to be 0.50, and displayed the tendency of increase with increase in the total length 140 cm. The gonadosomatic index of the fish was 2.5 for the female, and 1.7 for male.  The hepatosomatic index of female (2.5) and male (2.7) were similar. The type of ovarian development of Antarctic toothfish was group-synchronous type. In the ovaries of growing stage, initial vitellogenic oocytes with approximately 150 ㎛ of egg size was observed mainly. The egg size of mature oocytes presented approximately 800 ㎛e. As the result of H-E staining, eosinophilic yolk materials and vacuolar oil droplets were interspersed within the cytoplasm. The egg size of ripe oocytes were approximately 1,000 ㎛. Eosinophilic yolk materials are distributed within the medulla of cytoplasm, and combined multiple vacuolar oil droplets were existed in the cortical section of the cytoplasm. Histological testicular type of Antarctic toothfish was testicular lobule type, and the testicular lobule was composed of numerous testicular cysts. In the testis of growing stage the cysts became more definite gradually, and spermatogonia and spermatocytes occupied most of the cortex of the testicular lobule. It was possible to observe spermatids that illustrated basophilic reaction in H-E staining within the expanded testicular cysts in the mature stage. In the ripe stage, inner cavity of testicular lobules was occupied by spermatozoa of basophilic in H-E stain. Frequency of ovarian development stages of Antarctic toothfish showed the highest proportion with 45.4% at the ripe stage, and followed by the growing stage with 25.9% and mature stage with 28.7%. Frequency of testicular developmental stages demonstrated the highest proportion with 67.0% for the matuer stage, and followed by growing stage with 24.2% and ripe stage with 9.9%. The group maturity in accordance with the total length (TL) categories of Antarctic toothfish displayed 80% for female in larger than TL 100 cm categories and almost 100% for male in larger than TL 150 cm categories.