RESPONSES OF JUVENILE LARGEMOUTH BASS Micropterus salmoides TO DIETARY EPA AND DHA-RICH OILS

In recent years, the aquaculture industry has faced a rapid change in the raw materials used in feed formulations with a departure from marine-based to terrestrial plant-based nutrient sources that do not supply the n-3 HUFAS eicosapentaenoic (EPA) and docosahexaenoic acids (DHA). The indispensability of these n-3 HUFAS in the diet of Largemouth bass (LMB) remains unclear.   Therefore, the objective of this study was to evaluate the responses of LMB to dietary EPA and DHA-rich oils.

A 10-week feeding trial was conducted using twelve isonitrogenous and isolipidic diets, and different levels (0, 1 and 2%) and ratios (20:80, 30:70, 40:60, 50:50, 60:40, 70:30, and 80:20%) of EPA and DHA. An n-3 fatty acid depleted diet (1) containing 0.27% n-3 fatty acids and 0.05% EPA+DHA, and a linolenic acid (LNA) rich (4.35%) diet (2) were formulated using coconut oil and linseed oil, respectively. Six additional diets were formulated to contain 1% EPA+DHA at the abovementioned ratios using EPA-rich a DHA-rich fish oils. A final set of 3 diets were formulated to contain 2% EPA+DHA at 20:80, 50:50, and 80:20% ratios.

At the end of the feeding trial, the production performance of LMB was unaffected by the various EPA: DHA ratios. However, contrast analyses on performance parameter data showed that: i) LMB fed diets with 1 or 2% EPA+DHA displayed higher (P<0.05) weight gain and feed efficiency (FE) than those fed the LNA-rich and EPA/DHA-free diet (2), suggesting LMB has a limited ability to synthesize EPA and DHA from LNA to meet physiological needs for maximal growth and FE; and ii) the lack of differences (P>0.05) between LMB in the n-3 fatty acid depleted and LNA-rich groups indicated a low dietary requirement for LNA. Whole-body fatty acid composition data will be presented.

Our current results suggest LMB requires around 1% n-3 HUFAS in the diet for maximum growth and FE. If the current results are supported by whole-body fatty acid composition data, additional investigations to determine the quantitative requirement are warranted.