New Zealand’s sole commercial finfish aquaculture species is Chinook salmon (Oncorhynchus tshawytscha), a cold-water species at risk from increasing water temperatures. Diversification of farmed fish species can help mitigate this risk. We investigated the feasibility of manipulating the spawning of Australasian snapper (Chrysophrys auratus) and producing juveniles for sea pen culture in the Marlborough Sounds by early summer, when natural spawning occurs.
Water temperature and photoperiod were manipulated to induce spawning of captive broodstock in late winter. Tank water temperatures were cooled to 11°C by early July (winter). Between July and late August seawater temperature was progressively increased to 20°C, where it was held until spawning, which occurred without hormone intervention in late August. Eggs were incubated and larvae cultured in 5000-L self-cleaning tanks. A progression of live feed was used, beginning with enriched rotifers on 2 days post hatch (DPH) and progressing to Artemia on 20 DPH. Juveniles were weaned to commercial pellet feed (0.2–0.5 mm) by 35 DPH. At 99 DPH, 2550 juveniles under partial sedation (10 ppm Aqui-S™) with supplementary oxygen were transferred to a sea pen located in Beatrix Bay in the Marlborough Sounds. The sea pen was an 18-m polar circle sub-divided into four sub-pens, each approximately 216 m3 in volume. Commercial pellet feed was provided at 1.5% of body mass per day, delivered during daylight hours at approximately 90-min intervals by an automated drum feeder.
The growth performance of the late-winter spawned cohort was compared with that of a cohort of juveniles produced in November 2019 and grown in 5000-L tanks under ambient conditions. At 10 months post hatch tank-cultured fish had reached a mean length of 124 ± 8 mm (± SD; n=318), compared with 163 ± 8 mm (n=257) for sea pen-cultured fish. This trial presents an early case study for farming Australasian snapper in New Zealand and highlights one potential strategy to reduce the production time of this species.