The aim of this study was to evaluate the potential benefits of a commercial preparation of the medium-chain fatty acid (MCFA) heptanoate sodium salt (NOREL, HEPTON®) in a factorial design (2 x 2) with standard (20%, D1 and D2) or low (5%, D3 and D4) inclusion levels of fish meal (FM) as dietary protein source in an 11-weeks gilthead sea bream feeding trial. Heptanoate was added at 0.3% in D2 and D4 diets. Results of growth performance from 13-14 g to 81-84 g indicated a fast (SGR=2.2-2.3%) and efficient (FE=0.91-0.94) growth, with no changes in plasma IGF-I levels among fish fed the four experimental diets. Even so, an early impairment of FE, reversed by heptanoate supplementation, was observed in D1 FM-based diet. No signs of histopathological damage were found in any group, although higher hepatic glycogen depots were observed in fish fed both heptanoate-supplemented diets at the end of the trial. Other lasting heptanoate effects included changes on plasma antioxidant capacity, circulating cortisol and growth hormone (GH) levels, as well as in metabolic capabilities assessed by measures of oxygen consumption (MO2, mgO2/kg/h) and critical swimming speed (Ucrit) in swim performance tests. The pattern of respirometry metabolism closely resembled that of early FE, and the predictive value of plasma GH for different critical swimming speeds at fish exhaustion is suggested. Altogether, these results support the potential use of heptanoate to improve the healthy metabolic condition of farmed fish under sub-optimal rearing conditions.

This work has been carried out with financial support from NOREL S.A. and BioMAR. Additional funding has been received by Spanish MINECO project no. AGL2013-48560-R and Generalitat Valenciana (PROMETEO-FASE II/2014/085). M.C.P. was supported by MINECO through grant FPDI-2013-15741 and by CSIC PIE project no. 201740E013. J.A.M.-S. is supported by a Postdoctoral Research Fellowship (Juan de la CiervaFormación, Reference FJCI-2014-20161) from MINECO.

Trabajo presentado en el 11º Congreso de la Asociación Ibérica de Endocrinología Comparada (AIEC), celebrado en Vigo (España), del 13 al 15 de julio de 2017

Peer reviewed