Dietary Saccharina japonica is a natural and effective tool to fortify marine teleost black sea bream fillets with iodine: effects on growth, flesh quality, and serum thyroid hormones

Abstract

In the present study the effects of dietary Saccharina japonica on growth performance, flesh quality traits, and serum thyroid hormones (tetraiodothyronine (T4) and triiodothyronine (T3)) of juvenile black sea bream, Acanthopagrus schlegelii, were investigated. Seven diets containing graded levels of S. japonica (0, 0.1, 0.2, 1.2, 2.5, 5, and 10%) were formulated. Each diet was randomly assigned to sex replicate groups of 40 fish. After a 90-day feeding trial, the best growth performance was achieved in fish fed with the 2.5% S. japonica diet, with significantly higher weight gain rate (WGR) and lower feed coefficient (FC) than those fed with the other diets (P 0.05) on proximate composition of the whole body and the muscle. However, the content of n-6PUFA, n-3PUFA, and LC-PUFA in the muscle was significantly increased with the increasing level of dietary S. japonica. No differences in the flesh texture, cooked meat rate and water holding capacity were found among fish fed with different diets. It was further demonstrated that dietary S. japonica significantly fortify fillets with iodine (from 0.11 to 1.05 mg kg−1DM) and increased serum T4 and T3 levels. These results showed that the inclusion of up to 2.5% of S. japonica meal in diets could be beneficial to aquaculture of juvenile black sea bream, while higher inclusion levels resulted in significantly smaller fish. Moreover, the content of flesh iodine content quintupled in fish fed 2.5% up to 2.5%, confirming S. japonica as a natural and effective tool to increase the nutritional value of juvenile black sea bream.