REGULATION OF THE OMEGA-3 FATTY ACID BIOSYNTHETIC PATHWAY AND FATTY ACIDS BIOCONVERSION CAPACITY IN SELECTED RAINBOW TROUT

Currently, vegetable oils (VO) have become the primary alternative for fish oil (FO), as they are readily available, cost effective ingredients that contain high levels of essential C18 fatty acids (FA). Through a selective breeding program we have developed rainbow trout (Oncorhynchus mykiss) families which are improved in their ability to desaturate and elongate α-linolenic acid (18:3n-3; ALA) to produce the n−3 long-chain polyunsaturated fatty acids [LC-PUFA, eicosapentaenoic acid (20:5n-3; EPA), docosahexaenoic acid (22:6n-3; DHA)]. Therefore, we investigated the influence of fish oil (FO) and alternative oil sources [linseed (LO), soy (SO), canola (CO), coriander (CNO) and algae (AO) are rich in ALA, linoleic acid, oleic acid, petroselinic acid and DHA FAs respectively] on growth, muscle tissue FA composition, and lipid-related hepatic gene expression in trout. Six experimental diets (D1: 12%FO, D2: 12%LO, D3: 6% LO+2%SO+2%CO+2%CNO, D4:3%SO+3%CO+6%CNO = 3:3:6), D5: 6%LO+6%AO and D6: 12%AO) were fed in triplicate to trout (initial average weight 474 g) for 9 weeks.

Dietary source of vegetable oils significantly influenced the growth performance and muscle fatty acids profile (Fig. 1) in trout.

Highest weight gain % was observed in AO fed group (D6) whereas lowest value was found in D4.  Total saturated FA in muscle was affected by oil sources, diets with LO, SO, CO and CNO exhibited lower deposition than other oil sources. Among VO sources, highest EPA deposition was found in D5 (AO+LO; 1.74%) was similar to D2 (LO; 1.61%), whereas lowest value in D4 (1.26%) which was similar to D3 (1.45%).  EPA was absent in diet D4 but still fish muscle contained EPA which suggests that C18:1n-12 (petroselinic acid source CNO) might have converted to EPA. Highest and lowest PUFAs was observed in D2 and D4 respectively. Total EPA and DHA content were highest in D5 which is almost three times higher than D2 fed group. Expression analysis of genes related to the desaturases, dehydrogenase, elongase, carboxylase and de-carboxylase are being analyzed in hepatic and muscle tissue. Conclusively, algae oil can be used as an alternative source of oil to enhance the growth and increased the deposition of EPA and DHA in salmonid fillet for healthy food.