Lipid utilization and feeding of juvenile yellowtail flounder (Pleuronectes ferrugineus)

Whalen, Karen S. (1999) Lipid utilization and feeding of juvenile yellowtail flounder (Pleuronectes ferrugineus). Masters thesis, Memorial University of Newfoundland.

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Abstract

Interest in the culture of small flounder has increased in recent years due to their fast growth, low metabolic activity and good quality white flesh. Egg production and larval rearing of yellowtail flounder (Pleiironectes fernigineus) has improved and large numbers of juveniles are capable of being produced. However, protocols for grow-out of juveniles have not been developed and little is known of the nutritional requirements and feeding of this species. This study was undertaken as a preliminary investigation into feeding strategies for yellowtail flounder, in order to increase growth during the juvenile stage and to provide recommendations for the development of a species-specific diet. -- It is known that growth and food conversion are influenced by feeding frequency (number of meals per day) and experiments were set up to determine the best feeding regimes for optimal growth and food conversion of 0+ fish (under one year of age). Yellowtail flounder responded well to differing feeding regimes, and displayed good growth rates and low food conversion ratios (FCRs) when fed one, two, or four meals a day, and twice every other day. However, feeding frequency was shown to affect growth rates and food consumption. Behavioural observations showed that juveniles fed fewer meals per day ingested more pellets per feeding but were not as accurate at hitting the pellets as fish fed more often. Juveniles fed twice daily had the highest growth rates and lowest FCR, and it is recommended that fish at this stage of grow-out be fed twice per day. -- Body composition, condition factors and hepatosomatic indices (HSI) of wild and cultured yellowtail flounder were examined to make estimates for the possible formulation of diets for yellowtail, as well as to determine if present diets are adequate. Levels of storage fat were higher in the muscle and liver of cultured flounder and HSI was significantly higher (p < 0.05) in these fish, demonstrating an accumulation of fat. This, combined with higher condition indices in these fish, may suggest obesity, or a surplus in body fat due to caloric intake exceeding the amount of energy required, relative to wild counterparts. Total proportions of n-3 polyunsaturated fatty acids (PUFA) were higher in wild fish. Body composition of wild and cultured fish closely resembled the respective diets, and it is recommended that a diet be formulated for juvenile on-growing with high levels of protein, low levels of lipid and, within this lipid, high levels of PUFA. -- The effect of n-3 PUFA on the growth and body composition of cultured 0+ juvenile yellowtail flounder was examined in a third experiment. Yellowtail flounder did not display typical essential fatty acid (EFA) deficiency symptoms observed in other marine fish when fed levels of n-3 PUFA as low as 0.4% for twelve weeks. However, they show poor growth after four weeks and preferentially conserve PUFA in phospholipid of liver and muscle and accumulate triacylglycerol in the liver, suggesting the commencement of a deficiency. The increase in the ratio of DHA/EP A in polar tissues of yellowtail flounder was related to good growth. Neutral fatty acid composition in both liver and muscle was affected by diet. Results suggest that yellowtail flounder require 2.5% n-3 PUFA as a percentage of dry diet, with 10% lipid, for optimal growth and development. This level is higher than has been seen in the literature, and maybe due to its cold natural climate and wild diet of invertebrates, such as polychaete worms or amphipods.

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