Effect of dietary fluoride derived from Antarctic krill (Euphausia superba) meal on growth of yellowtail (Seriola quinqueradiata). 
Yellowtail (Seriola quinqueradiata) is the most important cultured marine fish in Japan.  Dietary fish meal for yellowtail in aquaculture was replaced with 0.0%, 15.4% and 100.0% Antarctic krill meal (KM0, KM15, and KM100) and with 0.0%, 15.4%, and 100.0% low-fluoride krill meal (LFK0, LFK15 and LFK100).  The fish was fed to duplicate fish groups for 92d (KM trial) or 75d (LFK trial), and fish growth was monitored.  Dietary fluoride (F(-)) concentrations (mgkg(-1)) were 110, 160, and 580 (KM0, KM15, and KM100, respectively) and 98, 120, and 190 (LFK0, LFK15, and LFK100, respectively).  The growth during the experimental period, weight gain, feed intake, specific growth rate, and feed efficiency in fish fed the KM100 diet were markedly lower than the other experimental groups, which showed no marked differences in growth performance.  After the experiment, dorsal muscle fluoride concentrations in each group were below the detectable limit (1 mg kg(-1)), but vertebral bone fluoride concentrations increased with increasing proportion of KM to 655 (KM0), 870 (KM15), and 2150 (KM100) mgkg(-1).  With increasing LFK in the feed, vertebral bone fluoride concentrations (mgkg(-1)) increased slightly from 500 (LFK0) to 655 (LFK15), and 695 (LFK100).  No histopathological changes were detected in the liver tissue in any experimental group.  It has been reported that the fluoride bioavailability was reduced with increasing water hardness, however, the dietary fluoride derived from KM exoskeleton accumulates in vertebral bones of marine fish with growth inhibition, as has already been shown for freshwater fish.  Vertebral bone fluoride concentrations in two krill-eating Antarctic marine fish in the wild were 33000mgkg(-1) (Champsocephalus gunnari) and 15000mgkg(-1) (Notothenia rossii), but they did not show any adverse effect of growth.  Therefore, fish bone fluoride accumulation apparently depends on fish species rather than the salinity of the habitat.  Consequently, krill exoskeleton must be removed during the processing of Antarctic krill if indeed these krill are to be used as fish feed.  However, LFK can completely replace dietary fish meal without apparent adverse effects.