Effect of dietary carbohydrate-to-lipid ratios on growth, lipid deposition and metabolic hepatic enzymes in juvenile Senegalese sole (Solea senegalensis, Kaup)

Abstract

A study was undertaken to determine the e¡ect of various dietary carbohydrate-to-lipid ratios on growth performance, whole-body composition and tissue lipid content in Senegalese sole (Solea senegalensis) juveniles. Data on the dietary regulation of key hepatic enzymes of the lipogenic and glycolytic pathways (glucose-6-phosphate dehydrogenase, G6PD; malic enzyme, ME; fatty acid synthetase, FAS; pyruvate kinase, PK and glucokinase, GK) were also generated. Four isonitrogenous (crude protein: 52% dry matter (DM)) diets were formulated to contain one of two lipid levels (11% and 21% DM). Within each dietary lipid level, the nature of the carbohydrate fraction (raw or extruded peas) was varied. Triplicate groups of 54 sole (initial body weight: 23.6 AE 1.2 g) were grown in recirculated seawater over 67 days. Fish were fed using automated feeders. At the end of the study, whole-body, liver, viscera and muscle samples were withdrawn for analyses. During the experimental period, the mean ¢sh weight about doubled in all treatments. No signi¢cant di¡erences were found in growth performance (ranging from 1.1% to 1.4% body weight day À1 ) among dietary treatments. High-fat diets increased whole-body fat content. Similarly, daily fat gain ranged from 0.54 to 0.78 g kg À1 day À1 and highest values were found in ¢sh fed high-lipid diets. Dietary treatments also affected tissue lipid content (liver, viscera and muscle), with highest values in ¢sh fed high-fat diets. The nat-ure of dietary carbohydrates had little in£uence on performance criteria, but a¡ected tissue lipid deposition. The activities of G6PD, ME and FAS were depressed by elevated levels of dietary lipid, con¢rming the inhibitory e¡ect of dietary fats on lipid biosynthesis. At both dietary lipid levels, ME and FAS activities were little a¡ected by dietary carbohydrate. Activities of PK and GK were not a¡ected by the starch level of the diets. In Senegalese sole juveniles, the lipogenic pathway is more susceptible to modulation by dietary means (particularly through lipid intake) than the glycolytic pathway.wAquatex 8074 from Sotexpro (Bermericourt, France): 22.5% CP, 1% lipid, 49% raw starch. zAquatex 8071 from Sotexpro: 23.7% CP, 1% lipid, 50% gelatinised starch. ‰Vitamin mixture (IU or mg kg À1 diet): DL-a tocopherol acetate, 60 IU; sodium menadione bisulphate, 5 mg; retinyl acetate, 15000 IU; 3000 IU; thiamin, 15 mg; ribo£avin, 30 mg; pyridoxine, 15 mg; B12, 0.05 mg; nicotinic acid, 175 mg; folic acid, 5 mg; ascorbic acid, 500 mg; inositol, 1000 mg; biotin, 2.5 mg; calcium panthotenate, 50 mg; choline chloride, 2000 mg. zMineral mixture (g or mg kg À1 diet): calcium carbonate (40% Ca), 2.15 g; magnesium oxide (60% Mg), 1.24 g; ferric citrate, 0.2 g; potassium iodide (75% I), 0.4 mg; zinc sulphate (36% Zn), 0.4 g; copper sulphate (25% Cu), 0.3 g; manganese sulphate (33% Min), 0.3 g; dibasic calcium phosphate (20% Ca, 18% P), 5 g; cobalt sulphate, 2 mg; sodium selenite (30% Se), 3 mg; KCl, 0.9 g; NaCl, 0.4 g.Aquaculture Research, 2004 Dietary carbohydrate/lipid...

Dietary lipid level affects growth performance and nutrient utilisation of Senegalese sole (Solea senegalensis) juveniles

“…In the present study, significant differences were found for hepatosomatic index among dietary treatments, but there was no clear association with dietary lipid level since L4 and L20 were similar. Hepatosomatic index values reported are in accordance with those found by Dias et al (4) in Senegalese sole but lower than other flatfish species such as turbot (18) and Atlantic halibut (12,16,24) and other marine teleosts such as European seabass (25) and gilthead seabream (29) .…”

“…Overall, liver lipids contribute to 0·1 % of final body weight and 1·7 % of total lipid content. Higher liver lipid contents were reported by Dias et al (4) in this species and in species such as turbot (18) and Atlantic halibut (16) . Moreover, Dias et al (4) observed that elevated levels of dietary lipids in Senegalese sole increased liver lipid content and depressed the lipogenic enzymic activity.…”

“…Higher liver lipid contents were reported by Dias et al (4) in this species and in species such as turbot (18) and Atlantic halibut (16) . Moreover, Dias et al (4) observed that elevated levels of dietary lipids in Senegalese sole increased liver lipid content and depressed the lipogenic enzymic activity. Different results were reported in turbot, where the absence of any change in hepatic lipogenic enzymes was associated with a low lipid deposition and relative absence of response to high dietary lipid levels.…”

“…Five isonitrogenous (56 % DM) experimental diets were formulated to contain increasing lipid levels (4,8,12,16 and 20 % DM; L4, L8, L12, L16 and L20, respectively). The dietary protein fraction was achieved by means of a variable blend of practical ingredients such as fishmeal, soyabean meal, maize gluten and wheat gluten, whereas increasing lipid levels were obtained by increasing fish oil inclusion.…”

“…Hence, five isonitrogenous diets (56 % dietary protein) with increasing dietary lipid levels (4,8,12, 16 and 20 % DM) were fed to satiation to triplicate groups of twenty fish (mean initial weight 10 g). Fifteen tanks were randomly assigned one of the five diets.…”