The use of chemical fish toxicants for coarse fish control is an accepted fisheries management practice in North America. In British Columbia the use of rotenone based fish toxicants is complicated by at least three factors: uncertainty of supply, cost escalations and increased concern about the effects and fate of chemicals used in lake rehabilitation programs. The need for chemical fish toxicants is valid in specific circumstances, and a literature review of approximately thirty chemicals used as fish toxicants suggests chlorine may be useful as a limited purpose fish toxicant. Chlorine hydrolyzes to form hypochlorous acid (HOCI) when added to ammonia free water, which then dissociate~1and maintains an equilibrium with hypochlorite ion (OCI ). The relative concentration of each form is determined by the pH and temperature of the water. Chlorine combines with ammonia to form chloramines, and being a strong oxidizing agent chlorine will react with reducing compounds present in lentic environments (eg. H2S). Laboratory bioassays indicate chlorine is quite toxic to flsh with 96 hr LC values ranging from 0.172 mg/L for rainbow trout (Salmo gairdneri) to 1.41 mg/L for black bullhead (Ictalurus melas). The primary toxizological mechanism of chlorine is oxi2ation of reduced iron (Fe ) in hemoglobin to methemoglobin (Fe ), resulting in an inability of the blood to carry sufficient oxygen and subsequent death by anoxia. At least three field tests have been conducted with results ranging from partial to complete kills, depending on the chlorine demand and concentration of residual chlorine in the water column. Chlorine may be a useful fish toxicant in limited situations where conventional fish toxicants should not be used (eg. drinking water sources) and the water body is quite small.
Ashley, Kenneth I.. 1989. The Use of Chlorine as a Possible Fish Toxicant. BC Ministry of Environment. Fisheries Project Report. RD20
Topic: Fish and Fish Habitats
Keywords: British Columbia, BC, Cl, Chlorinate, rainbow, bullhead, coarse fish control, pesticide, toxicology, water quality, chemical, fisheries management, Bioassay,