COMPARISONS OF GROWTH PERFORMANCE AND SURVIVAL OF LARVAL GIANT KOKOPU Galaxias argenteus FED VARYING RATIOS OF INSTAR-I AND INSTAR-II Artemia NAUPLII

Giant kōkopu (Galaxias argenteus) are a threatened, amphidromous fish species endemic to New Zealand. The larvae of this species are one of five making up the whitebait fishery,  a local delicacy with a market price of NZ$150 /kg and considerable aquaculture potential . However, in current production the Artemia  feed regime (LD1) accounts for a significant proportion of production costs,  inhibiting commercialization. Therefore,  the purpose of this study  is  to optimize the live feeding regime  to improve the financial feasibility of cultured giant kōkopu.

Three experimental live food treatments (Table 1), for feeding larval giant kōkopu  were tested over a 28 day period starting on the first day of feeding (3DAH).  Larvae were reared in round, 20 L tanks in RAS with water 35 ppt and 16-18 °C. Each tank, initially stocked with 2000 larvae, received 3 g of feed three times a day at 0830, 1230 and 1630 hours throughout the experimental period. Each feed treatment was conducted in three randomly selected replicate tanks.

After 28 days larvae in the LD2 treatment achieved the greatest growth , with length and mass being greater than that of the LD3 which in turn was greater than LD1. From day 11 onward LD1 had significantly greater mortality than the other  two  diets. There was no difference in total productivity between  LD2 and LD3, but both were greater than LD1 (Fig.1). The extrapolated time to harvest was significantly different amongst groups with LD2 to achieve harvest weight at 74 DPH, LD3 78 DPH and LD1 80 DPH (Fig. 1). Consequently, switching to the LD2 or LD3 diet would result in 21% and 25%, respectively, savings on Artemia costs as well as 17% and 9% respectively on artificial dry food costs.