The biomass of the California redworm hybridis abiologically valuable feed additive for farm animals, poultryand fish. Worms contain a large amount of protein, lipids,vitamins and trace elements. The chemical composition ofworm biomass depends on the nutrient medium on whichit was grown. Worms are able to accumulate trace elementsfrom the nutrient medium in their body. Using this property,we conducted research on the biomass of worms enrichedwith Cobalt with the prospect of its furthe rusein fishfeeding. It was found that increasing the number and weightof worms depends on the content of Cobalt in the nutrientmedium. The in troduction of 20 mg/kg of Cobalt in to thenutrient medium increased the number and weight of wormsweighing 0.4-0.8 g, respectively, by 38.0% and 40.4%. Anincrease in the number of immature worms by 32.2% wasdetected. By adding 40 mg/kg of Cobalt to the nutrientmedium, the umber and weight of worms increase by 45.9and 51.1%, respectively. The introduction of Cobalt in theamount of 160 mg/kg resulted in a decrease in the numberof worms weighing 0.4-0.8 g compared to the experimentalgroups by 6.5-27.7%. It was found that at a dose of Cobalt160 mg/kg, the number of small worms decreased relativeto the experimental groups by 24.0-50.7%. There was adecrease and weight of young worms relative to control by22.4%.It is established that with increasing cobalt content in thenutrient medium increases its concentration in the biomassof worms. The highest content of Cobalt was found in thedrymatter of the biomass of worms grown on a nutrientmedium to which was added the test metalin the amount of160 mg/kg.The biomass of worms grown on a nutrient medium towhich was added 40 mg/kg of the investigated metal canbeuse das a protein supplement with high cobalt content infish feeding.

Key words: vermiculture, wormbiomass, metalaccumulation, nutrient medium, Cobalt, atomicabs orptionspectros copy.