High dietary levels of MSB, 2,400 mg per kg, had no adverse affects on growth, survival, blood coagulation or the number of erythrocytes of young brook trout (Salvelinus fontinalis) (Poston, 1971b). Neither did high dietary concentrations, 2,000 mg per kg, of MNB have adverse affects on the growth, survival and blood coagulation of rainbow trout (Oncorhynchus mykiss) (Marchetti et al., 1995).
However, extended feeding trials with small, 0.18 g, Atlantic salmon (Salmo salar) fed a ration supplemented with 30 mg per kg of MSB or the molar equivalent of K1 over 28 weeks indicated the possibility of vitamin K3 toxicity. Fish fed this ration displayed reduced growth and increased mortality compared with animals fed an equivalent quantity of vitamin K1 (Grisdale-Helland et al., 1991). Unfortunately, the vitamin premix was top-dressed onto commercial pellets for this study. The poor performance of fish fed MSB could have been due to the fact that the MSB was oxidized or leached from the pellets. It is also possible that MSB is used less efficiently than vitamin K1. Further research is required to ascertain any toxicity of elevated dosages of these compounds over long periods. In a study with amago salmon (Oncorhynchus rhodurus), 1.5 g, fed 40 mg of menadione per kg of diet, no toxicity symptoms were seen after the 16-week feeding period (Taveekijakarn et al., 1996b).
