Reevaluating Polyunsaturated Fatty Acid Essentiality in Channel Catfish

Abstract

AbstractChannel Catfish Ictalurus punctatus reportedly require alpha‐linolenic acid (18:3[n‐3]) for normal growth. However, contradicting studies suggest that elevated dietary levels of this fatty acid might cause growth inhibition, and diets containing linoleic acid (18:2[n‐6]) alone or in combination with 18:0 and 18:1(n‐9) may support growth as well as fish oil (FO)‐based diets containing increased levels of long‐chain (LC) polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (20:5[n‐3]), docosahexaenoic acid (22:6[n‐3]), and arachidonic acid (20:4[n‐6]). Further complicating the understanding of essential fatty acid (EFA) requirements in Channel Catfish are conflicting reports suggesting that feeding LC‐PUFAs can either enhance or suppress growth. We evaluated growth performance and fatty acid composition of juvenile Channel Catfish that were fed seven diets containing n‐3 and n‐6 C18 PUFAs and/or LC‐PUFAs in different combinations: a positive control containing menhaden FO, a negative control containing hydrogenated soybean oil, and experimental diets containing hydrogenated soybean oil amended with ethyl esters of 18:3(n‐3); 18:3(n‐3) and 18:2(n‐6); 22:6(n‐3); 22:6(n‐3) and 20:4(n‐6); or 20:5(n‐3), 22:6(n‐3), and 20:4(n‐6). After 18 weeks, we observed no differences in growth or conversion efficiency. However, fish that were fed diets supplemented with C18 PUFAs and LC‐PUFAs numerically outperformed those fed the FO‐based positive control feed. Tissue fatty acid profiles generally mirrored that of the diet provided, except that saturates were underrepresented in the tissues. Channel Catfish that received the EFA‐free negative control feed or the diets supplemented with 18:3(n‐3) and 18:2(n‐6) or 20:4(n‐6) and 22:6(n‐3) developed elevated ratios of 22:5(n‐6) : 22:6(n‐3), whereas an elevated ratio of 20:3(n‐9) : 20:4(n‐6) was observed among fish that were fed the 22:6(n‐3) supplemented diet. Our findings suggest that C18 PUFA and LC‐PUFA diets appear to equally satisfy the EFA requirements of this species; however, intact dietary LC‐PUFAs should be carefully balanced to avoid antagonistic effects of surplus n‐3 LC‐PUFA on n‐6 LC‐PUFA biosynthesis.