Dietary calcium supplementation reduces the bioavailability of fluoride from krill shell and NaF in rainbow trout (Oncorhynchus mykiss) reared in fresh water

The use of Antarctic krill (Euphausia superba) in fish feeds may be limited by a high fluoride level. The aim of this experiment was to investigate the bioavailability of dietary fluoride from either krill shell or sodium fluoride (NaF) to rainbow trout (Oncorhynchus mykiss). The second aim was to investigate if the fluoride bioavailability was affected by adding calcium to the feed. Five experimental diets were produced; one control diet and four test diets containing 700 mg fluoride kg− 1 either from NaF or from krill shell, with or without added calcium chloride (15 g Ca kg− 1). Triplicate groups of fish were given one meal in excess of appetite prior to sampling. Five fish from each replicate tank were terminally sampled for blood; 0, 1, 3, 6, 9, 12, 15, 18, 24, and 36 h postprandial. Fluoride in blood plasma was used as an indicator of fluoride absorption. Fish fed NaF showed a clear peak in plasma fluoride of 1.17 mg l− 1 3 h postprandial, followed by a rapid decline. The fish fed krill shell did not obtain a clear peak but had a maximum fluoride plasma concentration (Cmax) of 0.32 mg l− 1 3 h postprandial. The addition of dietary calcium reduced the fluoride uptake in fish fed the NaF diet by nearly 100%, while adding calcium to the diets with krill shell reduced the uptake of fluoride to nearly the half. To conclude, fluoride from krill shell had a lower bioavailability than fluoride from NaF. Dietary calcium was an efficient way to reduce the fluoride uptake of rainbow trout reared in fresh water.