Microbial biomass in tilapia feed

Microbial biomass produced with industrial residues can be used as sources of proteins and antioxidants in fish feeds. The practice results in reduced amounts of waste to treat and discard and so brings benefits to the industry and to the environment. The aim of this experiment was to evaluate the growth and the oxidative status of tilapia fed microbial biomass and the quality of its flesh. Nile tilapia (26.84 ± 1.03 g) were fed one of experimental diets for 76 days. Treatments included a negative control diet (without microbial biomass), a control diet supplemented with 0.01% vitamin E (VE), and diets containing three types of microbial biomass in two concentrations (0.25 and 0.5%): R. gelatinosus (RG25 and RG50), S. cerevisiae (SC25 and SC50), and S. platensis (SP25 and SP50). The growth and the oxidative status of the animals and the physical, chemical and bromatological parameters of the flesh quality were evaluated. Adding microbial biomass to diets decreased plasma total oxidant status, malonaldehyde and leukocyte respiratory burst, increased the total antioxidant status and did not affect the blood biochemical parameters. All treatments had similar growth parameters, except feed conversion ratio that was lower for RG50 than for negative control group. In the flesh, the use of the microbial biomass lowered the thiobarbituric acid reactive substances and increased redness (except for S. cerevisiae), carotenoid deposition (except SC25) and protein content and improved the n-6/n-3 ratio of the fillets without interfering with the texture. RG25, SC25 and SP50 increased eicosapentaenoic acid on the fillets and RG50 had a positive effect on the animals’ growth. So, it was concluded that the use of the microbial biomass provided an antioxidant effect in blood plasma and improved the feed conversion ratio of the animals, decreased the lipid oxidation and increased protein content, pigmentation and carotenoid deposition in the fish flesh, without imparting a negative impact on the animals` health. (AU)