Reproductive ecology of Antarctic toothfish, Dissostichus mawsoni (Norman, 1937) (Actinopterygii: Nototheniidae), in the Antarctic waters (SSRUs 58 and 88)

Total numbers of Antarctic toothfish collected in the CCAMLR Conservation Zone were 600 fish which consist of 306 fish from the 58 area and 294 fish from the 88 area during February through March, 2016. Female ratios were found to be 0.49 in both areas, showing higher female occurrence with higher total length. The ratio of female among the 857 specimens of Antarctic toothfish collected from the 58.4.1 area and 88.3 area within the CCAMLR Conservation Zone during December, 2016 to March, 2017 was found to be 0.53, and displayed the tendency of increase with increase in the total length 140 cm. The type of ovarian development of Antarctic toothfish was group-synchronous type. The results in 2016 are as follows. The average gonadosomatic index of the fish was found to be 2.16, with 2.57 for female and 1.77 for male. Frequency of ovarian development stages of Antarctic toothfish showed the highest proportion with 41.9% at the mature stage, and followed by the growing stage with 40.6% and ripe stage with 17.5%. The group maturity in accordance with the total length (TL) categories of Antarctic toothfish displayed 50% for female in larger than TL 120.1 cm categories and almost 100% for male in larger than TL 180 cm categories. And the results in 2017 are as follows. The average gonadosomatic index of the fish was found to be 3.88, with 4.18 for female and 3.53 for male. Frequency of ovarian development stages of Antarctic toothfish showed the highest proportion with 62.7% at the mature stage, and followed by the ripe stage with 19.9% and growing stage with 17.5%. The group maturity in accordance with the total length (TL) categories of Antarctic toothfish displayed 50% for female in larger than TL 130.1 cm categories and almost 100% for male in larger than TL 170 cm categories. The main spawning season is estimated after May.