Incubation of halibut yolk sac larvae improved by addition of freshwater and oxygen
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Halibut fry has been produced regularly by scientific and commercial institutions since late 80- ties. The yearly number of halibut fry produced have, however, not fulfllled the optimistic expectations. This could partly be explained by lack of appropriate yolk sac rearing methods. Halibut larvae has, compared to other marine fish species, a long-lasting yolk sac period. Newly hatched larvae are poor developed and are very sensitive to handling. Two main methods have been used for halibut yolksac rearing; small stagnant and large flow-through incubators. The flow-through incubator has recently been modified, resulting in higher survival rates and simpler operating procedures. The modifications include a flow-through salinity gradient and thereby exclusion of the traditional mechanical outlet sieve. Oxygen is added at the bottom of the incubators to promote an ideal free distribution of the larvae in the water column and to avoid low oxygen tensions.