Combined replacement of fish meal and oil in practical diets for fast growing juveniles of gilthead sea bream (Sparus aurata L.): Networking of systemic and local components of GH/IGF axis

Abstract

Growth performance and growth regulatory pathways were examined in juvenile gilthead sea bream fed diets containing largely plant-based ingredients. Four isonitrogenous and isolipidic extruded diets with a low level (20%) of fish meal inclusion were formulated with graded levels of a vegetable oil mixture (17:58:25 of rapeseed: linseed: palm oils) replacing fish oil at 33, 66 and 100% (33VO, 66VO and VO diets). All diets were supplemented with lysine (0.55%) and contained soy lecithin (1%). Daily growth coefficients and feed efficiency over the course of an 11-week trial were almost identical in fish fed the FO, 33VO and 66VO diets. The VO diet reduced feed intake and growth without significant effects in proximate whole body composition, nitrogen or energy retentions. The highest concentration of plasma levels of insulin-like growth factor-I (IGF-I) was found in fish fed the 33VO diet. The lowest concentration was attained in fish fed the VO diet, whereas intermediate values were found in fish fed FO and 66VO diets. An opposite trend was found for circulating levels of growth hormone (GH), probably as a result of a reduced negative feedback inhibition from circulating IGF-I. Hepatic expression of IGF-I and GH receptor type I (GHR-I) was regulated in concert and mRNA levels paralleled plasma levels of IGF-I. Hepatic IGF-II and GHR-II were expressed in a more constitutive manner and no changes at the mRNA level were detected. In the skeletal muscle, IGF-I and GHR-I mRNAs did not vary significantly among groups. By contrast, IGF-II mRNA was up-regulated in fish fed the control diet, whereas the highest amount of GHR-II mRNA was attained in fish fed the 66VO diet. All together, these results suggest different growth compensatory mechanisms mediated by IGF-II and GHR-II at the local tissue level. These new insights prompted us to propose that practical diets low in marine ingredients can be used over the productive cycle of gilthead sea bream when essential fatty acids are supplied above the requirement levels.

Effects of dietary fish oil substitution by Echium oil on enterocyte and hepatocyte lipid metabolism of gilthead seabream (Sparus aurata L.)

“…Therefore, HUFA are essential fatty acids (EFA) for marine fish, and are important as structural components of cell membranes Marsh, 2008), eicosanoids precursors (Tocher, 2003;Bell et al, 2006;Villalta et al, 2007) and regulators of gene expression (Zheng et al, 2005;Miller et al, 2008;Leaver et al, 2008). The fatty acid profile of VO, together with this poor ability of marine fish to convert C 18 polyunsaturated fatty acids (PUFA) to HUFA, lead to important changes in the fatty acid composition of flesh of fish fed VOs, which include decreased n-3 HUFA and increased fat and LA contents Menoyo et al, 2004;Bell et al, 2006;Benedito-Palos et al, 2007;Díaz-López et al, 2009;Fountoulaki et al, 2009). Excessive consumption of VO and,has been related to some detrimental effects on health of fish (McKenzie, 2001;Sargent et al, 2002;Montero et al, 2003Montero et al, , 2008.…”

“…In this sense, up to 50-70% substitution of FO by VO has been reported to maintain the correct growth and health of some marine fish species including seabream and seabass Montero et al, 2003;Menoyo et al, 2004;Mourente et al, 2005;Benedito-Palos et al, 2007;Díaz-López et al, 2009;Fountoulaki et al, 2009). However, research is now focused at identifying VOs or blends that avoid excessive deposition of fat and LA, provide a good n-3/n-6 HUFA ratio, and maximize potential for conversion of C 18 n-3PUFA to EPA and DHA.…”

“…Gilthead seabream, Sparus aurata L., is the most important marine fish species in Mediterranean and Canarian aquaculture, and several studies have shown that it can generally be grown well on diets with FO partially replaced by VO Caballero et al, 2003Caballero et al, , 2004Menoyo et al, 2004;Benedito-Palos et al, 2007;Díaz-López et al, 2009;Fountoulaki et al, 2009). However knowledge of seabream lipid metabolism is still incomplete compared to other fish species, such as salmonids, turbot, and seabass Rodríguez et al, 2002;Mourente et al, 2005;Bell et al, 2001Bell et al, , 2002Bell et al, , 2006Tocher et al, , 2004Fonseca-Madrigal et al, 2006).…”

Molecular characterization and expression analysis of six peroxiredoxin paralogous genes in gilthead sea bream (Sparus aurata): Insights from fish exposed to dietary, pathogen and confinement stressors

“…To analyze the effect of three types of challenging experimental conditions on PRDX gene expression, samples were obtained from earlier studies already published [36,39,40]. The infection trial was performed by exposure of juvenile fish (134 g initial body weight) to E. leei-contaminated effluent [40].…”

“…The chronic exposure to Enteromyxum leei, a commonly occurring intestinal parasite in gilthead sea bream [35], was chosen as infection model. The total replacement of fish oil with a blend of vegetable oils in plant protein-based diets was chosen as a model of nutrient deficiencies in essential fatty acids (EFA) with detrimental effects on growth [36,37] and antioxidant capacity [38]. High rearing density was also selected as a common aquaculture stressor to assess the stressmediated response in a pair-fed model [39].…”