Digestibility, postprandial ammonia excretion and selected plasma metabolites in European sea bass (Dicentrarchus labrax) fed pelleted or extruded diets with or without wheat gluten

The effects of diet processing technology on digestibility, postprandial am monia excretion rates and plasma concentration of ammonia, glucose and chol esterol (CHOL) were determined in European sea bass. Four dietary treatment s were compared: diet EO (extruded basal fish meal diet); diet PO (pelleted basal fish meal diet); diet E30 (extruded, 70% basal diet plus 30% wheat g luten) and diet P30 (pelleted, 70% basal diet plus 30% wheat gluten). Each dietary treatment was assigned to triplicate groups of fish (body weight: 2 00 g). Levels of ammonia-N excretion from fish fed the different diets were measured in water samples taken from culture tanks every 2 h. At the end o f the experiment, plasma samples from 3 fish per diet, taken in alternative tanks every 2 h during 24 h, were assayed for ammonia, glucose and cholest erol determination. Nutrient digestibility was not affected by the diet pro cessing methods used. Wheat gluten showed high apparent digestibility coeff icient (ADC) values for protein, energy and organic matter. Postprandial am monia excretion values showed maximum values between 4 and 10 h after the m eal depending on treatment. Daily cumulative total ammonia excretion rates were lower in fish fed fish meal based diets than in those fed diets contai ning 30% wheat gluten. Irrespective of dietary formulation, fish fed extrud ed diets showed lower ammonia excretion than those fed the dry pelleted die ts. Postprandial values for plasma ammonia ranged between 3 and 8 mg ml(-1) and the pre-feeding values were reached 24 h after feeding in all treatmen t groups. Maximal levels of plasma glucose (120-180 mg ml(-1)) appeared wit hin 6 to 10 h after feeding. Plasma cholesterol levels were lower in sea ba ss fed diets containing 30% wheat gluten than in those fed diets containing fish meal alone as the: dietary protein source. (C) 1999 Elsevier Science B.V. All rights reserved.