Early hatch: a strategy for safe downstream larval transport in amphidromous gobies

The downstream migration to sea of newly-hatched larvae of amphidromous fishes exposes them to the risk of irreversible starvation if migration takes too long. Some fishes, especially sicydiine gobies, exhibit early hatch of eggs, often less than 48 h after fertilisation, and the newly-hatched larvae are at a very early stage of ontogeny, with no functional mouth or fins, no functional eye, and little pigmentation in the eye or elsewhere. This may facilitate survival as it means that downstream migration takes place when plenty of yolk remains, minimising the risk of starvation. Additional behaviours, such as positive phototaxis, continual swimming up into the water column, and hatching during elevated river flows, may also have contributed to rapid downstream transport and survival.