Characterization of whitebait (Galaxias maculatus) respiratory rates to optimize intensive culture carrying capacities

Galaxias maculatus is an osmeriform native fish of the Southern Hemisphere, in which the crystalline larvae is considered as a luxury delicacy, for this reason, it has been commercially exploited in Chile, Argentina and New Zealand. However, the fisheries have been rapidly decreasing due to the overexploitation and the predation of introduced species. Because of these events, there is a need to determine a carrying capacity for an intensive fish culture. In order to optimize stocking densities for fish culture, this paper proposes objectives to determine oxygen consumption (OC) rates, dissolved oxygen concentrations that produce signs of hypoxia and the average time elapsed between food intake and peak OC in G. maculatus. In the oxygen experiments under routine metabolism conditions, we found that G. maculatus adults and whitebait showed signs of asphyxia at dissolved oxygen concentrations between 1.3 and 2.2 mg L-1 and that adults tolerated dissolved oxygen levels as low as 1.3 mg L-1. The results showed that G. maculatus individuals with an average weight of 0.04 g consumed 0.048 mg O(2) h-1, whereas individuals with an average weight of 1.4 g consumed 0.345 mg O(2) h-1. Galaxias maculatus increased the OC rate by 31%, from 0.39 to 0.51 mg O(2) h-1 g-1, occurring 14 min after food intake. The carrying capacities for industrial cultures of G. maculatus, were estimated using an allometric equation (OC=0.2363 x W0.612), a water flow rate of 1 m3 h-1 and an input oxygen concentration of 10 mg L-1 at 12 degrees C. The density culture of whitebait (4 g) can be allowed to reach 8-11 kg m-3; therefore, these stocking densities reduce the risk of hypoxia and mortality, ensuring the appropriate growth and feed conversion rates.

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