Saturated Fatty Acids Limit the Effects of Replacing Fish Oil with Soybean Oil with or without Phospholipid Supplementation in Feeds for Juvenile Cobia

Abstract

The high cost and limited availability of fish oil makes plant-derived lipids attractive for aquafeed manufacturing, but replacing fish oil with these lipids can result in long-chain polyunsaturated fatty acid (LC-PUFA) deficiencies. Fatty acid metabolism, specifically the efficiency of LC-PUFA utilization, may be influenced by the dietary saturated fatty acid (SFA) content versus that of C₁₈ polyunsaturated fatty acids (PUFAs). We assessed the growth and tissue composition of Cobia Rachycentron canadum (55.3 ± 0.2 g initial weight [mean ± SE]; 10 fish/tank, 3 tanks/diet) fed diets (∼49% protein, ∼10% lipid) containing fish oil; 22:6(n-3)–amended standard, partially hydrogenated, or fully hydrogenated soybean oil; and these same soybean oils supplemented with soybean lecithin for 8 weeks. Although survival (range = 97–100%), final weight (160–189 g), and feed conversion ratio (1.40–1.52) were unaffected by diet, differences were observed in weight gain (185–241%), specific growth rate (1.87–2.19% body weight/d), and feed intake (2.94–3.44% body weight/d). Significant effects of soybean oil type on final weight, weight gain, feed conversion ratio, specific growth rate, and feed intake were noted, with standard soybean oil generally outperforming the other soybean lipids when oil types were pooled across phospholipid supplementation treatments, whereas phospholipid supplementation had no significant effect on any of the performance measures. Differences in dietary fatty acid profile yielded differences in tissue composition. Feeding standard soybean oil resulted in the most greatly modified profiles, whereas the profiles of fish fed fully hydrogenated, completely saturated soybean oil were most similar to those of the fish oil–fed fish. The magnitude of profile change was greatest in the liver and fillet tissues and smallest in the eye and brain tissues. Although further research is necessary to demonstrate whether SFA-rich lipids can effectively reduce the LC-PUFA requirements of Cobia, it is clear that SFA-rich oils offer a strategic advantage in minimizing the effects of fish oil replacement on tissue fatty acid profile.

Received April 15, 2012; accepted July 13, 2012

ACKNOWLEDGMENTS

We thank the Illinois Soybean Association, Virginia Sea Grant, Commercial Fisheries and Shellfish Technologies, and the International Initiative for Sustainable and Biosecure Aquafarming for providing funding and support for this research. We also thank Brendan Delbos, Steve Urick, and Brian Gause for their assistance in completing the feeding trial, harvesting tissue samples, and processing feed samples, respectively. We thank Archer Daniels Midland and Omega Protein, Inc., for the donation of the feedstuffs used in the experimental feeds. We also thank Luís A. Sampaio for his assistance in identifying and evaluating Yamamoto as a participant through the International Initiative for Sustainable and Biosecure Aquafarming student exchange program.

Notes

In fatty acid designations of this nature, the number to the left of the colon is the number of carbon atoms in the compound, the number immediately to the right of the colon is the number of double bonds, and the number after the hyphen indicates the position of the first double bond from the methyl end.