More Judicious Use of Fish Oil in Cobia Feeds: I. Assessing the Relative Merits of Alternative Lipids

Abstract

AbstractLimited availability and high prices underscore the need to use fish oil more judiciously in aquafeeds. Most alternative lipids contain little to no n‐3 long‐chain (LC) polyunsaturated fatty acids (PUFAs). If alternative lipids are fed exclusively, growth performance may be impaired and tissue fatty acid composition may be altered in fish such as the Cobia Rachycentron canadum. Alternative lipids that are rich in saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs) may increase the efficiency of LC‐PUFA metabolism and may limit or attenuate the tissue LC‐PUFA loss associated with fish oil sparing. Cobias (weight [mean ± SE] = 77.4 ± 0.2 g) were fed diets containing either fish oil (control) or a 50/50 blend of fish oil and standard soybean oil, partially hydrogenated soybean oil, fully hydrogenated soybean oil, pork lard, or beef tallow. After 8 weeks, the feed conversion ratio (mean ± SE = 1.56 ± 0.04), weight gain (180 ± 6%), and specific growth rate (1.83 ± 0.04% of body weight/d) were equivalent among groups. Dietary fatty acid profiles influenced tissue composition; fatty acid profiles of control fish were more similar to those of fish that received higher levels of SFAs and MUFAs than to those of fish that were fed higher levels of C18 PUFAs. The SFA‐ and MUFA‐rich lipids, such as fully hydrogenated soybean oil and beef tallow, may be useful in reducing the fish oil quantities needed in Cobia feeds while maximizing fillet LC‐PUFA content.