Effects of the protein/carbohydrate ratio of extruded diets on protein synthesis, protein growth and body composition in juvenile brown trout (Salmo trutta)

• Published in: Aquaculture international 2006-08, Vol.14 (4), p.337-353
• Main Authors: Viaplana-Marin, I, Fernandez-Borras, J, Blasco, J
• Format: Article
• Language: English
• Subjects: Accretion; Alternative energy; Alternative energy sources; amino acids; animal growth; Biodegradation; blood glucose; blood plasma; body composition; body fat; body protein; body weight; Diet; dietary carbohydrate; dietary protein; digestible energy; digestible protein; feed composition; fish culture; fish feeding; Fish feeds; Freshwater; glycogen; Insulin; muscle tissues; nutrient retention; Nutrition; Protein synthesis; Proteins; Salmo trutta; trout
• ISSN: 0967-6120; 1573-143X
• DOI: 10.1007/s10499-005-9036-8

High levels of protein in fish feeds result in higher costs and nitrogen waste. Therefore, studies focused on protein substitution by alternative energy sources are necessary. Here we examine whether the protein:carbohydrate ratio in extruded diets affects protein-turnover parameters and the main tissue components in brown trout. Juvenile fish were adapted to two extruded diets: one higher in protein and lower in carbohydrate, C: 45/28 and the other higher in carbohydrate and lower in protein, HC: 37/40. Gross energy was 19 MJ kg-¹ DM in both diets. Protein and lipid digestibility were high and similar in both groups ([almost equal to]90%), whereas total and carbohydrate digestibility and digestible energy were lower in the HC-fed group than in the C-fed group. Consequently, when fish were adapted to the diets, plasma levels of glucose and insulin differed between diets. HC-group presented higher plasma glucose levels and lower plasma insulin levels than C-group. Protein synthesis rates in white muscle, liver and whole body did not differ significantly between diets. In contrast, protein accretion rate of white muscle and whole body were significantly lower in the HC group, indicating an increase of protein degradation in these tissues and a decrease of synthesis retention efficiency. In spite of the daily protein intake of HC group was lower than C-group, the anabolic stimulation efficiency was increased by 34% in HC group. Protein and lipid contents in white muscle and liver were stable throughout the experiment. No hepatomegalia or increased fat deposition was observed in fish fed HC. Differences in specific growth rates (C: 0.88%; HC: 0.77%) were associated more with the lower protein consumption rate and the lower level of digestible energy in fish fed HC than with the higher dietary carbohydrate content of the diet.