Evaluation of krill (Euphausia superba) meal as a partial replacement for fish meal in rainbow trout (Oncorhynchus mykiss) diets

We studied partial replacement of fish meal (FM) by krill meal (KM) and how fluoride from KM enriched-muscles and bones of rainbow trout reared in freshwater affected these fish. Diets that replaced FM with KM at proportions of 0, 7, 15 and 30% (control, KM7, KM15, and KM30) were fed to groups of rainbow trout for 92 days and growth was observed. In fish fed KM7 and KM15, weight gain (WG), feed intake (FI) and specific growth rate (SGR) were unchanged compared with fish fed the control diet, but in fish fed KM30, WG, FI and SGR significantly decreased. After the experiment, fluoride concentration in dorsal muscles of each experimental group was below the detected limit (1 mg/kg), but in vertebral bones, the fluoride concentration increased with each increase in KM inclusion in the diets: 490 mg/kg (control), 755 mg/kg (KM7), 1100 mg/kg (KM15), and 2400 mg/kg (KM30). Tissue specimens of liver of each experimental group had no histopathological changes. Therefore, accumulation of fluoride in vertebral bones apparently adversely affected growth of the vertebral bones thus affecting the growth performance as shown by the decrease in WG, FI and SGR.