The effect of dietary docosahexaenoic acid (DHA) on growth, survival and pigmentation of California halibut Paralichthys californicus larvae (Ayres, 1810)

The California halibut (Paralichthys californicus) is a good candidate for aquaculture due to its good growth, survival and high commercial value. Several farms in the Western coast of North America are currently evaluating the potential of this species under commercial conditions. However, one of the main problems in the production of juveniles for commercial purposes is the high percentage of malpigmented fish obtained after metamorphosis (up to 80%). This problem seems to be related, among other things, to nutritional deficiencies during the larval period, in particular to the quantities and proportions of highly unsaturated fatty acids (HUFAs) in the diet. As a first approach to reduce malpigmentation, improve growth and determine the requirement for DHA in California halibut late larvae, we evaluated the effect of four levels of dietary DHA (0, 1, 2, and 4% of total fatty acids in the diet) on growth, survival, weaning success and pigmentation. DHA was administered to the larvae through enriched Artemia metanauplii. Larvae standard length and wet weight were taken during the initial stage of Artemia metanauplii supplementation (18 days post hatch, dph); at the beginning of the weaning period (50 dph); and at the end of the experiment (75 dph). We quantified the amounts of total fatty acids in 18 and 50 dph larvae. No significant differences on growth, survival and pigmentation as a result of increasing dietary DHA levels were found in 50 dph recently settled juveniles. However, larvae fed the highest DHA level resulted in the highest growth and survival at the end of the experiment (75 dph). Additionally, highest weaning success was achieved with this treatment. Significantly higher numbers of normally pigmented fish (ca., 33%) were obtained with the highest DHA level at 75 dph compared to the low DHA levels (0 and 5%). However, since this treatment resulted in the highest survival, part of the population had abnormal pigmentation (ca., 30% of the population). Based on a second order polynomial regression, the recommended DHA level in the diet for pre-metamorphic larvae to attain adequate growth and survival as estimated here for recently settled California halibut at 50 dph was 1.21% DHA of total fatty acids (TFA). However, for post-metamorphosis fish (75 dph) highest pigmentation rates, growth and survival are obtained with 2.40% DHA of TFA in the diet during the Artemia feeding period.