title: Avoidance tests with small fish: determination of the median avoidance concentration and of the lowest-observed-effect gradient.
abstract: The purpose of the present study was to develop sensitive, rapid, and easily quantified avoidance tests for small fish (Danio rerio) in order to provide important ecological information during toxicity assessments. Fish were exposed in three replicate linear flow-through chambers consisting of five compartments. The test system was found to provide a linear contamination gradient, with mean dilutions in each compartment of 90, 70, 50, 30, and 10%. Also, in the absence of a toxic gradient, the fish were uniformly distributed along the five-compartment chambers. Then the apparatus was evaluated by exposing fish to a concentration gradient of copper and a dilution gradient of a field sample contaminated with acid mine drainage (AMD). Avoidance was monitored at 24-h intervals up to 96 h of exposure. The avoidance of copper and AMD by D. rerio was confirmed. The apparatus enabled quantification of median avoidance effect concentrations or dilutions (EC50 or EDil50) and also lowest-observed-effect gradients, which express the minimum toxicant gradient eliciting avoidance, a parameter increasing the ecological relevance of the laboratory avoidance responses. For quantifying avoidance, a 24-h exposure was sufficient, as the 24- to 96-h EC50 and EDil50 values were similar. The avoidance response was easy and rapid to quantify, leading this test to routine use in environmental risk assessment.
authors.affiliation: IMAR-Instituto do Mar, Department of Zoology, University of Coimbra, Largo Marquês de Pombal, 3004-517 Coimbra, Portugal. matilde.santos@zoo.uc.pt
authors.forename: Matilde
authors.initials: M
authors.lastname: Moreira-Santos
authors.forename: Cristina
authors.initials: C
authors.lastname: Donato
authors.forename: Isabel
authors.initials: I
authors.lastname: Lopes
authors.forename: Rui
authors.initials: R
authors.lastname: Ribeiro
mesh_terms: D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D003300:Copper / Q000032:analysis / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D017753:Ecosystem; D005247:Feeding Behavior / Q000187:drug effects; D007220:Industrial Waste / Q000032:analysis; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000633:toxicity*; D015027:Zebrafish
chemical_list: D007220:Industrial Waste; D014874:Water Pollutants, Chemical; D003300:Copper