Use of Chlorella vulgaris in Rainbow Trout, Oncorhynchus mykiss, Diets to Enhance Muscle Pigmentation

ABSTRACT

The microalga, Chlorella vulgaris, which contains 0.2% carotenoids (ash-free dry-weight basis) (consisting of canthax-anthin and astaxanthin) was used as an ingredient in rainbow trout, Oncorhyncus mykiss, diets. A feeding trial was conducted to compare the quantitative effect of dietary algal biomass (ALG) incorporation on rainbow trout muscle pigmentation, with that obtained by feeding diets supplemented with a synthetic mixture of canthaxanthin and astaxanthin (MIX) equivalent to the quantities of these carotenoids found in the dry alga. After nine weeks of feeding, muscle of trout fed the algal diet contained slightly less total carotenoids (11.9 mg/kg dry muscle) than trout fed the diet containing synthetic carotenoids (13.3 mg/kg dry muscle). Comparison of total feed intake and weight gain were not significantly different (P > 0.05) among treatments. After the feeding trial, fish maintained on a diet containing no carotenoid supplements for eight more weeks (seventeen in total) had carotenoid concentrations of 9.1 mg/kg for fish fed the algal diet and 7.1 mg/kg for fish fed the diet containing synthetic pigments. Dry microalgal biomass was found to be a slightly less efficient muscle coloring ingredient for farmed trout than the commercially available pigments, yet proved adequate to achieve commercially acceptable color grades.