[Influence of some nutritional factors on the canthaxanthine pigmentation of the rainbow trout]

The present investigation was made to approve nutritionnal factors which affect the utilisation of food canthaxanthin by hatchery trout. Rainbow trout were obtained from a commercial trout farm, kept in running water and feeding in experimental pellets for 4 to 8 weeks. Five diets were tested (1-standard [7.5 u.i/g], 2-low protein content, 3-High lipid content, 4-non supplemented with vitamin A, 5-High vitamin A content [23 U.I./g]). All diets containing 250 mg of canthaxanthin per kilo of food, the fish were fed at the rate of approximately 2.5 p. 100 of their body weight per day. The estimation of canthaxanthin from fish tissues was accomplished as follows: the tissues were gomogeneized and extracted with several volumes of solvents. The solution containing all the pigment was evaporated. The purification of the canthaxanthin was obtained by column silica gel chromatography. The pigment was eluated with ethyl-ether as solvent. Quantitative assay of total carotenoïd was effected by spectre photometric estimation of optical density at 480 nm of this fraction dissolved in benzene. The carotenoïd composition of this fraction was studied by silica-gel thin layer chromatography. In these conditions:--it was shown by spectral studies that the canthaxanthins present in the diet are essentially those deposed in the flesh of the trout fed;--a series of experiment were made to examine the effect of composition of artificially composed feeds for pigmentation of the rainbow trout. The pigment deposition was found to correlate with the amount of lipids present in these diet. In this condition, the pigment is more dispersed with lipids present and the pigment absorption may be facilitated and later be deposed. 8 weeks alimentation are needed to observe the effect of these nutritionnal factor;--when the diet is non supplemented with vitamin A, the same quantity of canthaxanthin mixed with this food gives trout redder flesh than the standard diet. On an other hand, an antagonist effect of diet with high vitamin A content is demonstrated on the amount of the pigment deposed in the flesh of trout;--no effect of protein content of the diet was found in these experiments;--no effect of ratio calorie/protein of the diets with the intensity of deposed pigment in the flesh rainbow trout;--a correlation between neutral lipids of the tissue and the pigment deposed in the flesh of the trout fed with canthaxanthin was confirmed.