Safety evaluation of chloramine –T on ornamental zebra fish (Danio rerio) using LC۵۰ calculation and organ pathology

The need of aquarists for proper and safe disinfection of fish with Chloramine-T (CL-T) necessitates toxico/pathologic examinations.   This study assays toxicity level of CL-T and histopathologic changes of gills, liver, kidney and brain of treated zebrafish (Danio rerio). Groups of ۱۰ Zebrafish were treated with ۰ (control), ۵, ۱۰, ۱۵, ۳۰, ۵۰,۱۰۰ and ۲۰۰ mg/L of CL– T. Mortality was recorded at every ۶ hours until ۹۶h after the beginning of the treatment and lethal concentration for ۵۰% of population (LC۵۰ at ۲۴h and ۹۶h) was calculated. The histopathologic samples were taken from dying fish during the exposure period. Histopathological changes were not evident in organs of the control group. In the gills of treatment groups, congestion, edema, separation of epithelium of secondary lamella from basal membrane, fusion and hypertrophy of secondary lamella, telangiectasis and necrosis of lamella epithelium were observed. In the liver of treatment groups degenerative changes and necrosis of hepatocytes were visible.  The kidney samples represented hydropic degeneration, necrosis, dilation of periglomerular urinary space and hyaline droplets in renal tubules in high concentration. The brain of treatment groups showed spongiosis and increase in glial cells. Severity of these lesions was related to the concentration of CL-T. LC۵۰ ۲۴h for CL-T was ۴۲۸.۶۴۹ mg/L and LC۵۰ ۹۶h was ۱۱.۰۴۴ mg/L which reveals the low level of toxicity for few hours of treatment. The concentrations below ۱۵mg/L are reasonably safe and recommended for usage in D. rerio treatment during ۲۴h of bath.

Keywords:

Zebrafish , Chloramine - T , Histopathology , LC۵۰