Replacing dietary fish oil with palm fatty acid distillate improves fatty acid digestibility in rainbow trout, Oncorhynchus mykiss, maintained at optimal or elevated water temperature

An experiment was conducted to evaluate the interactive effects of dietary palm fatty acid distillate (PFAD) and water temperature on lipid and fatty acid digestibility in rainbow trout. Three isolipidic diets with 0, 10 or 15% (w/w) PFAD, at the expense of fish oil, were formulated and fed to triplicate groups of trout maintained at water temperatures of 15 or 20 °C. The apparent digestibility (AD) of fatty acids was measured using yttrium oxide as an inert marker. Increasing dietary PFAD, which contains mainly free fatty acids (FFA), led to a significant (P < 0.05) improvement in the AD of saturated fatty acids (SFA) but not that of total monounsaturated or polyunsaturated fatty acids in trout maintained at both water temperatures. High AD of total lipids (90–93%) was observed in all treatments. Based on fecal lipid class and fatty acid composition, this improvement in SFA digestibility was due in part to the increased absorption of the FFA as it bypasses the need for lipolysis. Elevated water temperature tended to cause a reduction in the AD of most fatty acids at each corresponding dietary treatment. The AD of individual fatty acids within each water temperature regimen generally decreased with increasing fatty acid chain length and increased with increasing unsaturation, irrespective of diet. In general, no significant interaction between diet and temperature effects on fatty acid digestibility was found.