REEVALUATING THE ESSENTIAL FATTY ACID REQUIREMENTS OF CHANNEL CATFISH

The availability of cost-effective feed ingredients for aquafeed manufacturing is a constraint for the aquaculture industry.  One of the most limiting factors is fish oil, a highly nutritious but costly ingredient that has traditionally served as the primary source of long-chain polyunsaturated fatty acids (LC-PUFA) required by some fishes. Various alternative fats and oils can be used to spare or replace fish oil, however, these feedstuffs generally don't provide appreciable amounts of LC-PUFA.  In order to maximize judicious use of fish oil supplies and formulate cost-effective aquafeeds, essential fatty acid requirements must be well-defined.  Recent evidence has suggested that reported essential fatty acid (EFA) requirements may not be fully accurate or complete.  Accordingly, we are reevaluating the fatty acid requirements of several commonly cultured fishes, including channel catfish Ictalurus punctatus, to determine whether n-3 and n-6 LC-PUFA or C₁₈ polyunsaturated fatty acids (C₁₈ PUFA) satisfy their EFA requirements.  Feeds were formulated to vary only in lipid source and composition, containing menhaden fish oil ("Fish Oil Control"); hydrogenated soybean oil ("EFA-free Control"); or soybean oil amended with ethyl esters of 18:3n-3 ("ALA"); 18:2n-6 and 18:3n-3 ("C₁₈ PUFA"); 22:6n-3 ("DHA"); 20:4n-6 and 22:6n-3 ("ARA + DHA"); or 20:4n-6, 20:5n-3, and 22:6n-3 ("LC-PUFA").  Diets were randomly assigned to quaduruplicate tanks (N=4) housing channel catfish (10 fish/tank, 5.62 ± 0.02 g/fish), and fish have been fed assigned diets once daily for a period of 15 weeks.  At the conclusion of the feeding trial (~ 20 weeks) production performance (e.g., survival, weight gain, feed conversion ratio, specific growth rate, feed intake, organosomatic indices) will be assessed and tissue samples will be collected for determination of fatty acid profiles.  Results presented will affirm the current understanding of EFA requirements in channel catfish (i.e., C₁₈ PUFA are adequate) and/or provide evidence regarding the merits of direct dietary supplementation with LC-PUFA.