THE EFFECT OF DIETARY FAT ON THE HEAT TOLERANCE OF GOLDFISH (CARASSIUS AURATUS)

Abstract

Three groups of goldfish were fed diets containing 25% fat. The diets for the three groups differed in the degree of unsaturation of these fats. Pilchard oil (iodine value 181.7), herring oil (iodine value 128.4), and lard (iodine value 66.2) were the fats used. Heat tolerance of the fish was then tested by holding them at a constant high temperature and observing the time of death. Variations in the ability of the groups to withstand high temperature were correlated with differences in the degree of unsaturation of their extracted fats. The iodine value of the herring oil diet was very close to that of the fats of the goldfish prior to feeding and no change in the value for fish fed on this diet was observed. Each of the other two diets changed the degree of unsaturation of the goldfish fats by approximately 54% of the maximum theoretical change. These changes modified the heat resistance of the fish. The degree of modification of heat tolerance, however, cannot be strictly correlated with the degree of change of unsaturation of fats and it is concluded that factors associated with differences in melting point rather than melting point of the fat itself are probably involved in heat resistance.