Reproduction, gamete supply and larval rearing of New Zealand turbot Colistium nudipinnis (Waite 1910) and brill Colistium guntheri (Hutton 1873): a potential new aquaculture species

New Zealand turbot Colistium nndipinnis (Waite 1910) and brill Colistium gu ntheri (Hutton 1873) were studied to assess their potential for aquaculture development. The reproductive cycle of wild fish showed a long spawning se ason from winter to summer, during which it is possible to obtain gametes. Both species have a diurnal ovulatory cycle, and gamete collection, by stri pping and fertilizing at sea, was most successful within 2-3 h before and a fter sunset. Male reproductive anatomy suggests that these flatfish spawn i n close proximity and that pair formation is highly likely. The eggs of bot h species have multiple oil droplets, turbot eggs being slightly larger (0. 99 mm diameter) with more droplets (18-55) than brill eggs (0.97 mm, 13-26 droplets). Hatching occurred approximately 84 h after fertilization at 14 d egreesC. Newly hatched turbot averaged 2.2 mm in length, and brill averaged 2.1 mm. First feeding began 4 days post-hatch (DPH). During larval rearing , rotifers were replaced by Artemia nauplii at 10 DPH. Metamorphosis commen ced at 12-15 DPH and was completed and the larvae settled by 45 DPH. Weanin g to inert foods began at 20-22 DPH (50 mg weight) and was completed by 57 DPH. Survival of turbot was 22.8% from fertilized egg to hatching, 7.3% thr ough incubation to 22 DPH and 2.1% through incubation to fully weaned juven iles. Weaning success for turbot from metamorphosis to 57 DPH was 31.5%.