Apparent digestibility of lipid and fatty acids in fish oil, poultry fat and vegetable oil diets by Atlantic halibut, Hippoglossus hippoglossus L.

An experiment was conducted to determine the apparent digestibility coefficients (ADC) of lipid and fatty acids of 5 experimental diets containing 18% lipid from the following sources: herring oil (HO), poultry fat (PF), flaxseed (FxO), canola (CO) and sunflower (SO) oils. Cholestane and chromic oxide were used as inert digestibility markers. Juvenile halibut (109.5 ± 27.6 g) were held in tanks equipped with fecal collection columns and fed the experimental diets for 2 weeks. The average lipid ADC (%) of FxO, CO, and SO diets were 94.8 ± 0.7, 93.4 ± 0.5 and 93.3 ± 0.2, respectively, and these values were higher than the ADC of HO (89.7 ± 0.1) and PF (89.8 ± 1.5) diets. The apparent digestibility of saturated fatty acids was lower than that of unsaturated fatty acids. The ADC of monoenoic fatty acids was lowest in groups fed PF diet (88.0 ± 1.3%) and highest with FxO diet (96.1 ± 0.3%), followed by groups fed CO and SO diets. Polyunsaturated fatty acids were better digested from the FxO diet and the PF diet showed the lowest values. The FxO and SO diets, which contained higher amounts of n-6 fatty acids, also showed relatively high ADC values of these fatty acids. These results suggest that vegetable oils are well utilized by juvenile halibut, and particularly FxO shows good potential to replace HO in commercial halibut feeds.