Evaluation of Water Fern (Salvinia molesta) as an Alternative Source of Omega-3 Polyunsaturated Fatty Acids for Cultured Tilapia

Abstract

Long chain omega-3 PUF As; EPA and DHA found mainly in fish, have been reported to have cardio-protective and other health benefits in humans. Unfortunately, capture fisheries cannot meet the demand for these fatty acids. As a result aquaculture has been on the increase with tilapia being one of the most cultured fishes. Recent studies however, have reported the presence of harmful combination of fatty acid (high n-6: n-3) in cultured tilapia as a result of inclusion of plant oil high in omega-6 in their diet. To achieve a low n-6: n-3 ratio, the aquaculture industry has shifted its attention to identifying alternative sources of n-3 for inclusion in fish feeds. The present study was conducted to evaluate Salvinia molesta an invasive aquatic weed as an alternative source of omega-3 for cultured tilapia. In triplicate groups of] 00, tilapia fingerlings weighing 0.35 ± 0.03g (mean ±SE) were fed on either commercial tilapia fingerling feed only, or commercial feed supplemented with S. molesta at 10, 20 or 30 %, for a period of 56 days. Lipids were extracted from feed and the fish fillet using the Folch method and fatty acid profile analyzed by gas chromatography. Results from this study showed that inclusion of S. molesta in the experimental diets had no significant impact on fish growth (p:S0.05). However, the concentration of n-3 in fish oil extracted from fish fillet increased as the level of S. molesta in diet increased (0.71 to 1.45mglg of feed, control & 30% S. molesta diet respectively). This also caused an overall decrease in the n-6: n-3 ratio in fillet from 6: 1 in fish fed commercial diet only to 4:1 in fish receiving 30% S. molesta. Although supplementation of commercial feed with S. molesta increased the amount of n- 3 in the experimental fish diet and the fillet, the effect was however minimized by the large amount of linoleic acid (n-6) in the commercial diet. Results from this study provide evidence that S. molesta is a good and potential source of n-3 for cultured tilapia that can be utilized at industrial scale.