ENHANCING THE ABILITY OF SALMONIDS TO CONVERT PLANT OILS TO EPA AND DHA

Aquaculture uses over 60% of the fishmeal and more than 80% of the available fish oil produced. Although this presents a serious problem for all of aquaculture, these dietary components are especially crucial for piscivorous and carnivorous species feeds. Commercial producers marketing aquaculture products for health benefits value fish oil because its use elevates levels of healthy omega-3 fatty acids in the product. Several different products including animal byproducts and plant proteins have been evaluated for their ability to replace fishmeal and fishoil and diet formulations using sustainable plant products to replace fishmeal and fishoil have shown substantial improvements compared to earlier formulated feeds. However, the utilization of sustainable products is still a problem in some fish, especially when trying to maintain omega-3 fatty acids levels of docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n-3) similar to that found in wild caught or farm raised fish reared with feeds containing levels of fish oil found in earlier generation of feeds.

Earlier research from our laboratory demonstrated that genetic variation exists, and is heritable for rainbow trout for the ability to actively convert plant oils (namely α-linolenic acid) and biosynthesize EPA and DHA and deposit it in muscle tissues. After one generation of genetic selection for this trait significant variation for the trait was noted within and between families. To better understand the biological mechanisms behind this trait, liver and muscle samples were taken from 36 second generation selected fish correlating with high, average, and low response as measured by EPA and DHA levels in muscle after being reared from 5 to 250 g on a complete plant-based diet. RNA and protein were isolated from the samples for RNA-seq transcriptomic and proteomic analysis. Some genes and a few proteins were found to vary significantly between compared groups but nothing currently has been determined to play a role in preferential deposition of specific fatty acids in the muscle. However, in the liver a greater number of genes and proteins were identified with some being linked to fatty acid processing.