Alternate lipid sources in fish meal-free production diets for rainbow trout
Projected increases in demand for fish oil have necessitated the evaluation of novel lipid sources for use in aquatic animal feeds. Two studies were conducted to determine the effects of various dietary lipid sources containing different ratios of n-6/n-3 polyunsaturated fatty acids (PUFA) on: (1) the lipid composition of various tissues and intestinal brush border membranes (BBM); (2) mineral absorption, and (3) bone mineral retention in rainbow trout. In the first study, fourteen practical diets varying in their n-6/n-3 ratios were fed to triplicate groups of rainbow trout weighing 1058 ± 5 g. The experimental diets contained either menhaden oil (MEN), flax oil (FLX), canola oil (CAN), cold-pressed soybean oil (CPS), solvent extracted soybean oil (SES), or 1:1 mixtures of menhaden and flax (MFX), menhaden and canola (MCO), menhaden and solvent extracted soybean (MSB), menhaden and cold-pressed soybean (MCP), flax and canola (FXC), flax and solvent extracted soybean (FXS), flax and cold-pressed soybean (FCP), canola and solvent extracted soybean (CSB), or canola and cold-pressed soybean (CCP) oils respectively as lipid source. Dietary lipid source did not significantly affect feed consumption, weight gain and other body characteristics. However, it affected the fatty acid composition of liver, muscle, bone and spinal cord lipids.^ Fish fed diets with high n-6/n-3 ratios (CPS, SES, CAN, CSB, and CCP) exhibited significantly lower tissue n-3 PUFA concentrations, lower 20:5n-3, lower 22:6n-3, higher n-6/n-3 ratios, and higher 20:4n-6/20:5n-3 (AA/EPA) than fish fed diets with low n-6/n-3 ratios. In the second study quadruplicate groups of fish weighing 1994 ± 4 g were fed MEN, FLX, CPS, MFX, MCO or FXC. Lower n-3 PUFA concentrations, especially 22:6n-3, were observed in BBM polar and neutral lipids of fish fed CPS. Calcium, magnesium, phosphorus and zinc absorption was lower in fish fed CPS, FLX and FXC. Concentrations of 20:4n-6 and ratios of n-6/n-3 PUFA and AA/EPA in bone polar and neutral lipids, were significantly higher in fish fed CPS. Bone ash content and mineral concentrations were not significantly affected by dietary lipid source. Results suggest that menhaden in combination with other oils, and flax oil can be used as alternate lipid sources in diets for rainbow trout. ^
Major Professor: Paul B. Brown, Purdue University.
Agriculture, Animal Culture and Nutrition|Agriculture, Fisheries and Aquaculture