Spawning behaviour and early development in the naked dragonfish Gymnodraco acuticeps

Abstract

Nesting sites of the naked dragonfish Gymnodraco acuticeps have been identified in 15–35 m water under fast ice adjacent to McMurdo Station, making it possible to examine embryonic development and early larval growth. Egg-laying (predominantly in October) is preceded by a distinctive whirling behavioural pattern driven by the male prodding the side of the female's abdomen. The eggs (3.42 ± 0.19 mm in diameter) are laid on rocks as a single adherent layer (c. 2500 per patch). Development is unusually protracted, the first cleavage occurring after about 24 hr at about −1.9°C. Hatching occurs about 10 months post-fertilization, beginning soon after the sun rises above the horizon. During this period one of the parents may act as a guard in an attempt to keep predators at bay. Upon hatching, the larvae (12.09 ± 0.36 mm long) swim towards the surface ice where they presumably seek refuge. Yolk absorption is complete in about 15 days. Larvae (grown in aquaria at a density of 0.7 larvae l⁻¹) display an average daily growth rate of 0.42% over nine weeks. Hatching in aquaria can occur up to 100 days in advance of that seen in the field, suggesting that under natural conditions hatching may be delayed until an appropriate stimulus (such as the return of the sun) is received.