Replacement of fish oil in plant based diets for Pacific white shrimp ( Litopenaeus vannamei)

Abstract

Due to economic pressures from high fish oil prices and from buyers and consumers requiring sustainable practices, the use of high levels of fish oils in aquafeeds is no longer desirable. The present study evaluated the replacement of marine fish oil (MFO) with alternative oils in a plant based diet. Litopenaeus vannamei juveniles (1.55 g) were stocked into 650 L circular tanks at 26 shrimp tank −1 and fed 13 experimental diets over a 58-day growth trial. Diets were formulated with soybean oil (SO) as replacement for MFO at inclusion ratios of 100:0, 50:50, 40:60, 30:70, 20:80, and 10:90 as MFO:SO. The next series of diets were formulated to keep n-3/n-6 ratios close to the ratio attained at 50% MFO replacement while removing MFO, this was done by increasing linolenic acid content through the use of linseed oil (LO), resulting in the following MFO:SO:LO ratios, 40:53.4:6.6, 30:56.9:13.1, 20:60:20, and 10:63.7:26.3. Three additional diets were evaluated which included a high LO (10:90 as MFO:LO) and a high soybean oil diet using a low linolenic acid acid soybean oil (LLSO) at a 10:90 ratio of MFO:LLSO. The final diet was a commercial diet which served as a reference. The results showed no statistically significant differences in final mean weight, growth, survival or FCR values of shrimp fed the various diets. Fatty acid (FA) profiles of tail muscle form shrimp fed the various lipid sources in general conformed to the lipids of the feed. Shrimp fed Diet 11, with 19.81 mg of linolenic acid per gram of diet had the highest amount of this FA in shrimp tail muscle (5.61 mg g −1 wet tissue) and a relatively high n-3/n-6 ratio of 1.15, but at the same time, practically the lowest content of eicosapentaenoic (4.07 mg g −1 wet tissue) and docosahexaenoic (2.04 mg g −1 wet tissue) acid among the dietary treatments. This response is typical for animals that cannot elongate and desaturate poly-unsaturated into highly-unsaturated FA (HUFA). As shrimp production was not influenced by lipid source or n-3/n-6 ratio, clearly a range of lipids could be used to support growth. However, as the optimal dietary approach for humans is to consume preformed n-3 HUFA by eating seafood, it would be best for farmed shrimp to retain high levels of n-3 HUFA and high n-3/n-6 ratios as found in wild caught shrimp.