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An 8‐week feeding experiment was conducted to provide preliminary information on essential fatty acid requirements of hybrid tilapia (female Nile tilapia Oreochromis niloticus × male blue tilapia O. aureus). Seven semipurified diets containing 30% crude protein from casein with 3.2 kcal available energy/g were supplemented with 5% of either lard (L), corn oil (C), cod liver oil (F), lard and corn oil (1:1, L–C), lard and cod liver oil (1:1, L–F), corn oil and cod liver oil (1:1, C–F), or lard, corn oil, and cod liver oil (1:1:1, L–C–F). Each diet was fed to three replicate groups of fish initially weighing 0.84 ± 0.02 g (mean ± SD) in 60‐L aquaria connected as a closed recirculating‐water system containing freshwater at 25 ± 1°C. Results indicate that significantly (P < 0.05) higher weight gain, feed efficiency (FE), protein efficiency ratio (PER), and protein deposition (PD) were associated with fish fed the diet supplemented with F. Among groups fed diets containing F, weight gain was significantly higher in fish fed L–C–F than in fish fed L–F and F. Fish fed L–C–F had significantly higher FE and PER values than those fed F, L–F or C–F. Protein deposition was significantly better in fish fed L–C–F than in fish fed L–F. Fatty acid compositions of liver and muscle in fish generally reflected the composition of the diet. These data suggest that n‐3 highly unsaturated fatty acid as well as n‐6 fatty acid are essential for maximum growth 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.

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