The effect of dietary Arachidonic acid concentration on Atlantic halibut (Hippoglossus hippoglossus) broodstock performance. Assessment of egg, milt and larval quality.

Abstract

In order to evaluate the impact of four different diets on halibut broodstock, eight tanks were set up. Each tank contained 15 females and 5 males. The four broodstock diet formulations contained 0.4% arachidonic acid (20:4n-6; ARA), (0.4g ARA/l00g dry feed), 0.6% ARA, a control feed not supplemented with ARA and a control feed in which a proportion of the fish meal was replaced with squid meal, to improve palatability. The experimental diets were fed for a period of 3 years. The spawning period was regulated by photoperiod. Four tanks spawned in May and the four others spawned in July. A pit tag was used to identify each fish. This allowed individual length and weight data to be collected every 2 months. During the spawning season, milt, eggs, at different developmental stages, and yolk sac larvae were sampled for subsequent biochemical analyses (lipids, fatty acids and prostaglandins). Fish fed the ARA enriched diets showed significantly better growth compared to the other two treatments. During the second spawning season, fish fed the 0.4% ARA diet showed significantly improved egg production while fish fed on the 0.6% ARA diet showed a delay in their spawning season and poor reproductive performance. Fatty acid analyses on eggs, yolk sac larvae and milt showed significant ARA uptake and deposition in relation to the diet. Broodstock females fed the 0.4% ARA diet produced early life stages with what could be regarded as an optimal DHA: EPA: ARA ratio. Furthermore, males fed the 0.4% ARA diet produced the best quality milt over an extended period.