Susceptibility of Brook Trout (Salvelinus fontinalis) Fry to a Liquid Formulation of Bacillus thuringiensis serovar. israelensis (Teknar®) Used for Blackfly Control

Exposure of brook trout (Salvelinus fontinalis) fry to 4500 and 6000 mg Teknar®∙L−1 for 45 min resulted in 20 and 86.4% mortality, respectively. At concentrations of 3000 mg∙L−1 and higher, fish became motionless and exhibited variable recovery within 2 h following contact, depending on concentration. Fish exposed to 6000 mg freeze-dried Teknar∙L−1, were not affected. Forty-eight hours of static exposure resulted in 1.33% mortality at 60 mg∙L−1, no mortality at 300 mg∙L−1, and 8% mortality for the controls; degradation of water quality may explain this response. Gas chromatographic analysis revealed the presence of 2% xylene in the formulation. Fish fed with chow contaminated with 30% (w/w) Teknar did not show any response. Considering the recovery and the absence of effects in 48-h static tests, the feeding test, and exposure to the freeze-dried formulation, we attribute the observed response to the effect of xylene a preservative agent of the formulation tested.