Lasting effects of butyrate and low FM/FO diets on growth performance, blood haematology/biochemistry and molecular growth-related markers in gilthead sea bream (Sparus aurata)

Four isoproteic/isolipidic plant protein-based diets were formulated to assess the lasting effects of feed additives and low fish meal (FM) and fish oil (FO) diet formulations on gilthead sea bream growth performance. FM was included at 23% in the control diet (D1) and at 3% in the other three diets (D2, D3, D4). Added oil was either FO (D1) or a blend of vegetable oils replacing 58% (D2) and 84% (D3, D4 diets) of FO. A commercial sodium butyrate preparation (NOREL, 70-BP) was added to the D4 diet at 0.4%. Each diet was allocated to triplicate groups of juvenile fish fed to satiety over an 8-month feeding trial (May-December). All fish grew efficiently from 15 g of initial body weight to 296-320 g with an overall feed efficiency (FE) of 0.95-1.01, although fish fed D3 and D4 diets showed transient growth impairments over the course of the first four weeks of the trial. Data on biometric indexes, whole body composition, haematology and blood biochemistry revealed a strong effect of sampling time in fish sampled atmid-summer (August) and late autumn (December). In contrast, the diet effect was mostly reduced to a few blood parameters. Low inclusion levels of FM reduced plasma haemoglobin levels (D2, D3), but these effects were reversed by butyrate supplementation (D4). The same phenomena occurred for total cholesterol with the highest circulating concentration of choline and IGF-I in fish fed the D4 diet during their summer growth spurt. At the transcriptional level, gene expression profiling of liver and skeletal muscle with a PCR-array of 87 growth markers provided additional evidence for an overall well-growth condition in all of the experimental groups. Up to 73 genes were found at detectable levels in the liver tissue, but only 13 were differentially expressed. Likewise, 84 genes were actively transcribed in the skeletal muscle, but only nine were differentially expressed in at least one experimental group. Butyrate supplementation reversed the up-regulated expression of inflammatory cytokines (TNF alpha) and muscle markers of cellular morphogenesis and protein breakdown (CDH15, CAPN3, PSMA5, PSMB1, UBE2N) in the muscle of fish fed the extreme D3 diet. These results support the use of low FM/FO diets alone or supplemented with feed additives, which have the potential to improve or reverse metabolic steady-states. Statement of relevance: Butyrate effect on low fish meal/fish oil diets. (C) 2015 Elsevier B.V. All rights reserved.