Effects of alternate feeding between fish oil‐ and terrestrially sourced oil‐based diets on fatty acid composition of different tissues of turbot

Abstract

Use of terrestrially sourced oils (TSO) in the diet easily causes reduction in long-chain polyunsaturated fatty acids (LC-PUFA) in farmed fish. Alternate feeding between fish oil (FO)- and TSO-based diets is a potential strategy for mitigating this LC-PUFA reduction. The present study, with turbot, was aimed at comparing the fatty acid-regulating effects of the alternate-feeding strategy in different tissue types, namely, muscle, liver and subcutaneous tissue around the fin (STF). The control group were fed the FO-based diet continuously for 13 weeks. Meanwhile, other groups were subjected to weekly alternation between the FO-based diet and diets based on TSO, namely, linseed oil, soybean oil, rapeseed oil, palm oil and beef tallow, respectively. Each dietary group had triplicate tanks, and each tank was stocked with 35 fish. Tissue samples were collected at the end of Week 9 and 13. At Week 9, significant differences among dietary groups were observed in LC-PUFA contents of all tissue types; at Week 13, the significant difference in muscle disappeared, but those in liver and STF remained. STF seemed more like a lipid storage site, with high contents of 18:1n-9 and 18:3n-3, but low LC-PUFA contents. Among all the treatments, alternate feeding between FO- and beef tallow-based diets resulted in the most similar fatty acid profile to the treatment with continuous FO feeding. This study added knowledge to the fatty acid composition of fish subcutaneous tissue, as well as to promising application of beef tallow in fish feed.