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acement of fish meal by other protein sources. In turbot, protein sparing by fats or carbohydrates does not seem to hold much promise. Turbot do not appear toutilise carbohydrates efficiently ŽAdron et al., 1976 .and high levels of lipid in the dietappear to have adverse effects on growth and body composition ŽBromley, 1980; Cacerez-Martinez et al., 1984; Andersen and Alsted, 1993; Danielssen and Hjertnes, 1993 . .
To our knowledge, so far, very few studies have dealt with the use of plant protein
Ž
sources as www.51lunwen.orgalternatives to fish meal in the diets for turbot or plaice Cowey et al., 1971;
.
Burel et al., 1998b . Corn gluten meal has a high protein level, is low in fiber, rich in vitamins B and E and is known to contain no antinutritional factors. CGM is however deficient of the amino acid lysine. In salmonids, a supplementation with lysine is required for diets containing CGM ŽKetola, 1982 .or wheat gluten ŽDavies et al., 1997 . .
The objectives of the present study conducted with turbot were Ž.1 to measure digestibility and amino acid availability of experimental diets containing graded levels of CGM, Ž.to evaluate growth performance of turbot fed diets in which fish meal was
2 gradually replaced by CGM, Ž.to evaluate the effects of CGM incorporation on plasma
3 cholesterol, triglyceride and thyroid hormone concentrations and plasma and dorsal muscle free amino acid concentrations.
2. Material and methods
2.1. Experimental diets
Five experimental diets were formulated. They contained a gradient of CGM in replacement of original fish meal. Diet 1 contained no CGM and served as control. Diets 2 to 5 contained 20, 40 and 57% of CGM replacing equal amounts of protein from fishmeal. Diets 4 and 5 had no fish meal and were supplemented with differing amountsof two amino acids, L-arginine and L-lysine ŽEurolysine, Amiens, France . . Inosine, a specific feeding stimulant for turbot ŽMackie and Adron, 1978; Mitchell and Mackie, 1983 , .was added in each diet at a level of 150 ppm. The ingredient and chemical compositions of diets are presented in Table 1 with the corresponding amino acid compositions in Table 2.
( )C. Regost et al.rAquaculture 180 1999 99–117    101
Table 1    
Ingredients and proximate composition of the experimental diets    
Experimental diets    
 1  2  3  4  5  
()Ingredients % ŽFish meal Norseamink.  52.00  31.00  14.00  –  –  
CGM  –  20.00  40.00  57.00  57.00  
Soluble fish protein concentrate  8.00  8.00  8.00  8.00  8.00  
Fish oil  3.00  4.50  5.50  6.50  6.50  
L-glutamate  –  2.50  2.10  1.30  –  
L-lysine  –  –  0.40  1.00  1.80  
L-arginine  –  –  –  0.20  0.70  
Middling wheat  5.00  5.00  5.00  5.00  5.00  
Extruded peas  29.99  26.99  21.99  15.99  15.99  
Mineral mixa  1.00  1.00  1.00  1.00  1.00  
Vitamin mixb  1.00  1.00  1.00  1.00  1.00  
Dicalcium phosphate  –  –  1.00  1.00  1.00  
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