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 hybrid tilapia (Nile tilapia Oreochromis niloticus × blue tilapia O. aureus). Eight isonitrogenous and isoenergetic diets containing various percentages of 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 initial body weight of 0.83 g (SD=±0.03). The fish were kept at 26±1°C in aquaria connected to a freshwater water-recirculating system. Tilapia fed diets with 2.0% or more CLO had a significantly (α=0.05) higher 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 (where 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 significantly. Tilapia fed a diet without any CLO had significantly lower growth performances and showed a typical n-3 deficiency, with the ratio of liver (20 : 3, n-9) and muscle (22 : 6, n-3) fatty acids greater than 0.4. This study lends more support to our previous report that besides n-6, hybrid tilapia may also require n-3 fatty acids for maximum growth.