Disentangling reproductive biology of the Patagonian toothfish <Emphasis Type="Italic">Dissostichus eleginoides</Emphasis>: skipped vs obligatory annual spawning,foraging migration vs residential life style

Patagonian toothfish Dissostichus eleginoides Smitt 1898, is an important commercially targeted Notothenioid species in South-Atlantic waters. In this study we aimed to clarify several aspects of reproductive biology of Patagonian toothfish in the Falkland Islands waters. Histological examination of female gonads indicates that with the beginning of maturation females maintain at least two populations of oocytes, suggesting that toothfish requires up to two years for oocytes development. Females become mature at an average size of 79.1 cm indicating a decrease of first maturity size if toothfish females in the Falkland Island waters. The majority of females spawn at the size from 101 to 130 cm total length. Distribution of reproductive phases shows an increase of females at developing stage in December and March prior to the spawning peaks in May and August respectively. However, the majority of the toothfish population consist of non-spawning individuals remaining in regressing phase (55.8 to 85.6%) including the spawning period. The skip-spawning for toothfish has been defined as reabsorbing non-reproductive and resting types. The abbreviation of oocytes development in the gonads was observed from 1 to 22.1% of females which omitted the spawning season. Most likely females which remain in the spawning area have the opportunity to spawn more often, whereas females which undergo foraging migration toward Northern parts of the Falklands waters return to the spawning ground less often. Females remain Northern area longer to accumulate necessary amount of energy. This hypnotise is supported by the presence of females in immature, developing and regressing phase throughout surrounding Falkland Islands waters. Presence of post-spawning females in regressing stage throughout the Falklands waters suggest that toothfish may undertake irregular spawning/foraging migration when favourable for spawning condition occur.