Study On Nutritional Physiology Of Essential Fatty Acids In Abalone Haliotis Discus Hannai Ino.

Two 120 day-feeding experiments were conducted to investigate the effects of dietary fatty acid on the growth and fatty acid metabolism of abalone, Haliotis discus hannai Ino. in circulated rearing system. Fish oil (enriched with C20:5n-3), soybean oil, linseed oil and palmitic ester were respectively used lipid sources to formulate four purified diets (crude protein 28%, crude lipid 3.5%) in Experiment 1. Five casein-gelatin-based purified diets with graded ratios of C18:2n-6 to C20:5n-3 (1.00:0.00, 0.75:0.25, 0.50:0.50, 0.25:0.75, 0.00:1.00, containing a fixed level of both C18:2n-6 and C20:5n-3) were formulated in Experiment 2. Each diet was randomly assigned to triplicate tanks, and each tank was stocked with 25 abalones. Abalone was fed once (18:00) daily with a feeding rate of 5%. During the experimental period, temperature was maintained approximately 18.0-25.0C, pH 7.4-7.8, salinity 31-35, and dissolved oxygen was more than 6 mg/1. Results showed that dietary lipid sources significantly influenced the growth of abalone (P<0.05). Growth rates in abalone fed the diets with supplementation of fish oil, soybean oil and linseed oil were significantly higher compared with the supplementation of palmitic ester. Abalone grew best when fed the diet with fish oil enriched with C20:5n-3 (P<0.05). The fatty acid composition in abalone was found to correlate well with dietary fatty acid composition (P<0.05). The growth of abalone was also significantly influenced by the ratio of dietary C18:2n-6 to C20:5n-3 and optimal ratio was found to be 0.25:0.75. This suggested that the combination of fish oil (enriched with HUFA) and vegetable oil (enriched with C18:2n-6) in diets was beneficial to the growth of abalone. The fatty acid analysis in diets and abalone indicated that abalone could transfer C18:2n-6 to C20:4n-6, and C18:3n-3 to C20:5n-3 through elongation and desaturation. However, the bioconversion capacityfor C20:5n-3 to C22:6n-3 was limited in abalone.