EFFECT OF DIET ON THE FATTY ACID COMPOSITION OF THE COPEPOD TISBE BIMINIENSIS

Success in rearing fish depends on the nutritional content of food offered to the larvae. The aim of this study was to test the effect of diets on fatty acid composition of the copepod Tisbe biminiensis Volkmann-Rocco, 1973 as a food source. The copepods were reared in 5 1 vessels with aeration at 29-31 degrees C, salinity 30-35, and natural photoperiod of 13 hours light/11 hours dark. The copepods were fed two diets: a mixture of microalgae Thalassiosira weissflogii and commercial fish food, and only the fish food. Lipids were extracted with chloroform and methanol and esterified by acid catalysis with BF3. Three replicates were used in each treatment. Fatty acids were identified by comparison of retention times and co-injection with standard Mix C4-C24 using GC and GCMS apparatus. Thirty-one and 29 fatty acids were detected on copepods fed mixed diets and fish food, respectively. The most abundant fatty acids in copepod fed mixed a diet were C18, C16, and C12. In the other treatment, predominant fatty acids were C18, C16, and C20:2. Thirty-one and 30 fatty acids were detected in the fish food and the microalgae, respectively. The predominant fatty acids of microalgae were C18, C21, and C20:2. For fish food, the predominant fatty acids were C16, C18, and C18:1n9. Essential fatty acids were detected and EPA and DHA contents of copepods fed mixture were significantly higher compared to those fed only ration, indicating that the mixed diet provided better source of HUFA for T biminiensis. However, its DHA level was lower than other harpacticoid copepods. This suggests that T biminiensis either needs to be fed a better quality diet, or be enriched with some fatty acids before they are offered to the cobia larvae. The copepod T biminiensis is capable of bio-converting fatty acid C18:0 into chains with 20 unsaturated carbons. T biminiensis fed mixed a diet or the fish food alone showed DHA/EPA ratios of 1.3 and 3.3, respectively, suggesting that this copepod species may be suitable for use in fish larviculture.