Measurement of Oxidation in Fish Oil and its Effect on Vitamin E Nutrition of Rainbow Trout (Salmo gairdneri)

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Abstract
Peroxide value (PV), anisidine value, and thiobarbituric acid (TBA) number were compared as methods for measuring oxidation in fish oils and fish diets. PV was the method of choice for estimating oxidation in the oil. Methods for measuring moderately oxidized oil after being mixed in the diets are discussed. Analyses of dietary samples revealed that the TBA numbers and percentages of polyunsaturated fatty acids were not greatly altered by the addition of moderately oxidized fish oil and by the long-term storage (24 wk) of the diet at room temperature. However, endogenous α-tocopherol levels in the diet were significantly (P < 0.05) reduced by both the addition of moderately oxidized oil and by 24-wk storage. The level of supplemental DL-α-tocopheryl acetate was not changed by the treatments. Fish fed the experimental diets showed no significant differences in body weight gain, feed/gain ratio, mortality, carcass composition, hematocrit, or plasma glutathione peroxidase activity. However, the α-tocopherol concentration in their livers was significantly (P < 0.05) increased by raising the levels of supplementary DL-α-tocopheryl acetate.Key words: oxidized oil, vitamin E, diet stability, Salmo gairdneri