| Summary: | This study aimed to assess the health and welfare of turbot juveniles fed with experimental diets containing graded levels of a mixture of plant protein, by means of blood chemistry analyses including stress and metabolic indicators. Four extruded isonitrogenous (51%) and isolipidic diets (16%) were manufactured by Skretting ARC, Stavanger, Norway: a reference diet (diet D) contained 50% fish meal and three other diets in which fish meal was progressively reduced to 35% (diet C), 20% (diet B) and 5% (diet A) by proportionally increasing the level of wheat gluten meal, soybean meal and soy protein concentrate. Turbot juveniles (Initial weight 9.68 g ± 0.98 g) were reared in 500 l square recirculating tanks at 18°C (n= 55 fish per tank). The trial was performed in triplicate and lasted 9 weeks. Blood was withdrawn from the caudal vein, serum was collected after centrifugation and stored at -80°C for analyses of cortisol (COR), glucose (GLU), osmolality (OSM), non-esterefied fatty acids (NEFA), triglycerides (TAG), cholesterol (CHO), total protein (TP), urea (BUN), aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phophatase (ALP). Biometric measurements and autoptical analysis were also performed. One-way ANOVA and discriminant analysis were applied to data set to test the effects of dietary treatment. Experimental diets significantly affected growth and metabolic status of turbot juveniles (ANOVA p<0.05 for PT, LT, COR, TAG, CHO, NEFA, TP, BUN, ALP). At the end of experiment, a progressive reduction of size and serum concentration of TAG, CHO, NEFA, TP, BUN levels were observed in fish fed C, B and A diets, whereas a significant cortisol increase was found only in fish fed diets containing equal or less than 20% of fish meal. Although not significantly, the levels of GLU and ALT were higher in A and B diets compared to C and D. Only CHO, NEFA and BUN were different between C and D diets. Osmolality as well as hepatosomatic and splenosomatic indices did not change among diets. ...
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