Calculating incubation times and hatching dates for embryonic elephantfish (Callorhinchus milii)

Abstract

An experimental approach was used to calculate the spawning times and hatching dates for the oviparous chondrichthyan, Callorhinchus milii. The duration of the embryonic stages, from the formation of the area opaca to hatching, was determined at water temperatures of 10°, 15° and 20°C for egg cases collected from the Marlborough Sounds and Canterbury Bight, using novel observation techniques. Development times for temperatures 9–20°C were calculated using these data, enabling the prediction of spawning times, development times and hatching dates at four spawning sites in New Zealand. In the Marlborough Sounds, peak spawning was in April, with a predicted development time of 32 weeks and a predicted hatching time in November. In Canterbury Bight, peak spawning was in December, with a 25-week predicted development time, and a predicted peak hatching in late May. At Dunedin, peak spawning was in December, predicted development was 34 weeks and hatching would occur in late July. In Te Waewae Bay, peak spawning during January yielded a predicted 34-week development period and peak hatching in late August.