Effect of dietary cod liver oil on growth and fatty acids of juvenile hybrid tilapia

An 8-week growth trial was conducted to determine the effects of different levels of cod liver oil (CLO) on growth and tissue fatty acids of male hybr id tilapia (Nile tilapia Oreochromis niloticus X blue tilapia O. aureus). E ight isonitrogenous and isoenergetic diets containing various percentages o f dodecanoic acid and CLO (5.0:0, 4.5:0.5, 4.0:1.0, 3.5:1.5, 3.0:2.0, 2.0:3 .0, 1.0:4.0, 0:5.0) were fed to triplicate groups of tilapia with an initia l body weight of 0.83 g (SD = +/-0.03). The fish were kept at 26 +/- 1 degr eesC in aquaria connected to a freshwater water-recirculating system. Tilap ia fed diets with 2.0% or more CLO had a significantly (alpha = 0.05) highe r specific growth rate, feed efficiency, and protein deposition than those fed diets with lower CLO. Percent muscle and liver fatty acid 18:3, n-3 (wh ere the ratio is the number of carbon atoms to the number of double bonds, and n designates the position of the first double bond); 20:5, n-3; 22:5, n -3; and 22:6, n-3 increased with increasing CLO, but 20:3, n-9 decreased si gnificantly. Tilapia fed a diet without any CLO had significantly lower gro wth performances and showed a typical n-3 deficiency, with the ratio of liv er (20:3, n-9) and muscle (22:6, n-3) fatty acids greater than 0.4. This st udy lends more support to our previous report that besides n-6, hybrid tila pia may also require n-3 fatty acids for maximum growth.