Effect of dietary
carbohydrate-to-lipid ratios on growth, lipid deposition and metabolic
hepatic enzymes in juvenile Senegalese sole (Solea senegalensis,
Kaup)
J. Dias, R. Rueda-Jasso, S. Panserat, L.E.C. da
Conceição, E.F. Gomes, M.T.
Dinis-2004
Aquaculture
Research, 35(12): 1122-1130
Abstract:
A study was undertaken to determine the effect 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±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samples were withdrawn for analyses.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 fish weight about doubled in all treatments. No significant differences
were found in growth performance (ranging from 1.1% to 1.4% body weight day-1)
among dietary treatments. High-fat diets increased whole-body fat content.
Similarly, daily fat gain ranged from 0.54 to 0.78 g kg
-1 day
-1
and highest values were found in fish fed high-lipid diets. Dietary
treatments also affected tissue lipid content (liver, viscera and muscle),
with highest values in fish fed high-fat diets. The nature of dietary
carbohydrates had little influence on performance criteria, but affected
tissue lipid deposition. The activities of G6PD, ME and FAS were depressed
by elevated levels of dietary lipid, confirming the inhibitory effect of
dietary fats on lipid biosynthesis. At both dietary lipid levels, ME and FAS
activities were little affected by dietary carbohydrate. Activities of PK
and GK were not affected 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.
(CCMAR, University of Algarve, Campus de Gambelas,
8000-117, Faro, Portugal. E-mail of L.E.C. da Conceição: lconcei@ualg.pt)