Dietary sodium heptanoate helps to improve feed efficiency, growth hormone status and swimming performance in gilthead sea bream (Sparus aurata)

The potential benefits of a commercial preparation of heptanoate (NOREL, HEPTON (R)) were evaluated in an 11-week gilthead sea bream feeding trial (May-August), using a factorial design with four isoproteic and isoenergetic diets. Fish meal (FM) was added at 200 g/kg in D1-D2 diets and at 50 g/kg in D3-D4 diets, which also contained fish peptones and plant proteins as source of proteins. Heptanoate was added at 3 g/kg in D2 and D4 diets. All fish grew from 13-14 g to 81-84 g with an overall feed efficiency (FE) of 0.91-0.94. An early impairment of FE (weeks 1-4) was found with the standard FM-based diet (D1), but this detrimental condition was reversed by heptanoate, increasing FE from 0.88 in D1 fish to 0.99 in D2 fish. Further improvements were progressively diluted over time, remaining D2 and D3-D4 fed fish almost undistinguishable through all the trial. Heptanoate supplementation produced higher hepatic glycogen depots, but no signs of histopathological damage were found in liver or intestine. Other lasting heptanoate effects included changes in plasma antioxidant capacity, plasma cortisol and growth hormone levels, and measures of respirometry in swimming performance tests. Altogether, it supports the potential use of heptanoate to speed up adaptive and healthy metabolic states of farmed fish to cope with challenging culture conditions.