Reevaluating Polyunsaturated Fatty Acid Essentiality in Nile Tilapia

Abstract

AbstractNile Tilapia Oreochromis niloticus have a reported dietary requirement for the n‐6 C18 polyunsaturated fatty acid (PUFA) 18:2n‐6 (linoleic acid), but direct provision of the n‐6 long‐chain (LC) PUFA 20:4n‐6 (arachidonic acid) may be a more efficient approach. No quantitative requirement for n‐3 fatty acids has been formally recognized for tilapias, but beneficial effects of having both n‐3 and n‐6 PUFAs in the diet have been reported. To better understand PUFA essentiality in tilapias, we formulated diets to assess the growth performance and tissue fatty acid composition of juvenile Nile Tilapia (mean ± SD = 25.7 ± 0.2 g/fish) that were fed different combinations of n‐3 and n‐6 PUFAs: a positive control containing menhaden fish oil, a negative control containing hydrogenated soybean oil, and experimental diets containing hydrogenated soybean oil amended with ethyl esters of 18:3n‐3; 18:3n‐3 and 18:2n‐6; 22:6n‐3; 22:6n‐3 and 20:4n‐6; or 20:5n‐3, 22:6n‐3, and 20:4n‐6. After 7 weeks, weight gain, feed conversion ratio, and specific growth rate were significantly greater among fish that received the positive control feed than among fish that were fed the negative control feed. The addition of n‐3 and n‐6 PUFA supplements generally improved performance in most cases. No fish showed any gross indications of fatty acid deficiency, although significant differences in fatty acid deficiency indicator ratios (i.e., 20:3n‐9 : 20:4n‐6 and 22:5n‐6 : 22:6n‐3) were present in all tissues analyzed. Nile Tilapia that were fed an n‐3 PUFA‐free diet exhibited significantly elevated 22:5n‐6 : 22:6n‐3 ratios, indicating a developing n‐3 PUFA deficiency. Feeding n‐3 PUFAs—as 18:3n‐3, 22:6n‐3, or a combination of n‐3 LC‐PUFAs—had a corrective effect on these ratios, affirming the importance of a proper balance of n‐3 and n‐6 PUFAs to satisfy the essential fatty acid requirements of Nile Tilapia and further illustrating the ability of this species to satisfy physiological demand for LC‐PUFAs through de novo biotransformation of C18 PUFAs.