Natural Fish Oil Research Articles

Effects of dietary polyunsaturated fatty acid deficiencies on mortality, growth and gill structure in the turbot, Scophthalmus maximus

The preparation of fish oil concentrates containing only (n‐3) polyunsaturated fatty acids (PUFA) with different ratios of 20:5 (n‐3)/22:6 (n‐3) is described. Three groups of turbot were maintained on different diets containing: 1, 10% of the dry weight of the diet as natural fish oil, equivalent to 2.5% (n‐3) PUFA and 0–23% (n‐6) PUFA; 2, 10% of the dry weight of the diet as palmitic acid, i.e. no PUFA; 3, 8–7% palmitic acid and 1–3% of the dry weight as (n‐3 PUFA and negligible (n‐6) PUFA. Only the fish on the diet containing natural fish oil showed significant growth over a 15‐week period. In addition there were high mortalities on the two experimental diets (2 and 3). Changing the ratio of 20:5 (n‐3)/22:6 (n‐3) from 13–8 to 2–2 in the diet containing 1 3% (n‐3) PUFA and negligible (n‐6) PUFA markedly decreased the mortalities. Fish fed the two experimental diets (2 and 3) developed gross changes in gill structure involving the disappearance of chloride cells, a ‘sloughing off’ of the epithelium along the primary and secondary filaments and an accumulation of cellular material in the inter‐lamellar spaces. The tissue ultimately disintegrated to leave a skeleton of connective tissue and a mass of cellular material in the inter‐lamellar spaces. It is concluded that 22:6 (n‐3) is an essential fatty acid for turbot and that the gill epithelium is a sensitive indicator of this deficiency in this species.