Toxicity of Chlorine-Produced Oxidants to Arabian Killifish Embryos for Acute Developmental Stages Exposures

Abstract

Background: Fish embryos are excellent models for studies aimed at the understanding of toxic mechanisms and the indication of possible acute and chronic effects. Therefore, we present the use of Arabian killifish (Aphanius dispar) embryos, an indigenous species to the Arabian Gulf, to study the effect of chlorine-produced oxidants to marine organisms in the Qatari coastal area. Objective: The objective of this study is to develop chlorine toxicity data for the marine Fish Embryo Toxicity (mFET) test. The test is designed as a means to replace or refine the use of marine juvenile and/or adult fish in standard approaches evaluating toxicity of chemicals and effluents. Methods: Embryos were collected from a breeding stock of sexually mature Arabian killifish. Testing was initiated as soon as possible after fertilization of the eggs with exposure to aqueous concentrations of calcium hypochlorite (0.10 – 12.3 mg/l) for up to 240 hours. The investigated endpoints included; coagulated eggs, somite development, heartbeat, tail detachment, hatchability and post hatch mortality. Results: The results showed a developmental stage-dependent response to chlorine. During earlier developmental stages, chlorine had reduced effects on the embryos and the survival rate and hatchability were high, even at relatively high concentrations. In later developmental stages (pre to post hatch, eleutheroembryo), the embryos were significantly more sensitive to chlorine than in the early stages of development. The chorion, (membrane surrounding the egg), is believed to provide a barrier against chlorine in early stages of embryo development. Conclusions: Taking into account the findings presented here, Killifish embryos exhibit the ability to be an indicator organism for environmental risk assessments of the Qatari coastal area. Benefits include, animal alternative, ease of fish breeding, clarity of the embryos, reduced sample size, reduced waste generation and shorter study duration.