Effect of total replacement of dietary fish meal by low fluoride krill (Euphausia superba) meal on growth performance of rainbow trout (Oncorhynchus mykiss) in fresh water

This study aimed to totally replace fish meal (FM) in diets by low fluoride krill (Euphausia superba) meal (LFK). LFK was prepared by removing exoskeletons from dried whole krill to give a fluoride content of approximately one-fourth of krill meal (KM) at 230 ppm for LFK and 870 ppm for KM. Experimental diets replaced FM with LFK at the replacement proportions of 0.0%, 7.7%, 15.4%, 30.8%, 46.2% and 100.0% (control, LFK7, LFK15, LFK30, LFK46 and LFK100) and were fed to groups of rainbow trout (Oncorhynchus mykiss) in duplicate for 95 days in fresh water and growth was observed. In all experimental groups, feed intake, feed efficiency, specific growth rate and hepatosomatic index were unchanged compared with fish fed the control diet (P < 0.05). After 95 days, the fluoride concentration in dorsal muscles of the fish of each experimental group, except LFK100, was below the detectable limit (1 mg/kg), and in vertebral bones it was between 220 mg/kg and 420 mg/kg. However, the dorsal muscle and the vertebral bone of LFK100 contained 1 mg/kg and 1800 mg/kg of fluoride, respectively. Tissue specimens of the liver of each experimental group at 95 days had no histopathological changes. The total replacement of FM from LFK in diets was successful with no defects of growth performances. This study showed that krill protein had a nutritional value equivalent to FM.