Effects of Dietary Lipids on Fatty Acid Composition of Channel Catfish Fry

Abstract

Channel catfish (Ictalurus punctatus) fry were reared in flow-through troughs and circular tanks on practical diets supplemented with fish oil, soybean oil, or beef tallow. A control diet was also utilized which contained beef tallow at a reduced level. Fry reared on the fish oil diet increased in weight significantly more than fish fed the soybean oil and control diets. Survival was relatively poor because of water quality problems. Fry reared on the beef tallow diet exhibited poor growth and survival due to an Ichthyophthirius multifilis infestation and generally poor fish condition. Proximate analyses showed that body compositions among the four treatment groups were similar. In general, fatty acid compositions of the fry reflected dietary levels. Fry fed the fish oil diet contained high levels of linolenic family fatty acids, while fry reared on the soybean oil diet showed high carcass levels of linoleic family fatty acids. Fry reared on the beef tallow and control diets were intermediate in both total linolenic and linoleic family concentrations. Fry which received diets low in linolenic family fatty acids may have exhibited some utilization of linoleic acid (18:2ω6). A selective retention of original levels of linolenic family fatty acids from sac fry, or the elongation and desaturation of linolenic acid (18:3ω3), was also indicated. Increased levels of 20:3ω9, which is used as an index of essential fatty acid deficiency, occurred in fry reared on the beef tallow diet. Levels of this fatty acid may have denoted the beginning of essential fatty acid deficiencies in those groups of fry.