9357 - Laserfiche WebLink

Home Browse Search

'I . 1 1- "),, () () I r> e V 0'5' C,lf1 d ;- (Ii,! YY/ 2,( ISETA~/PRESS I (( ? Environmental Toxicology and Chemistry, Vol. 20, No.4, pp. 907-912, 2001 @ 2001 SETAC Printed in the USA 0730-7268/01 $9.00 + .00 . l EFFECTS OF COPPER ON OLFACTION OF COLORADO PIKEMINNOW I ~ DANIEL W. BEYERS* and MICHAEL S. FARMER Larval Fish Laboratory, Department of Fishery and Wildlife Biology, Colorado State University, Fort Collins, Colorado 80523, USA (Received 16 May 2000; Accepted 29 August 2000) Abstract~Effects of copper on olfaction of Colorado pikeminnow (Ptychocheilus lucius) were investigated by exposing fish for 24 or 96 h, then evaluating olfactory ability using a behavioral assay and observing olfactory structures using scanning electron microscopy (SEM). The behavioral assay measured a response known as fright reaction. Failure of exposed fish to demonstrate a fright reaction in the presence of skin homogenate assumed to contain fright pheromone was considered evidence of copper-induced loss of olfactory ability. Regression analysis was used to describe the response of fish as a function of copper concentration at each exposure duration. Olfactory ability declined with increasing copper concentration. For copper concentrations less than 66 fLg/L, olfaction was more sensitive to exposure at 24 h than at 96 h. This result suggests that physiological adaptation and recovery of sensory ability occurred despite continuous exposure in the 96-h treatment. Protective mechanisms induced by exposure may have reduced sensitivity to copper by 96 h. Systematic surveys using SEM to detect presence or absence of olfactory receptors confirmed results of behavioral assays. Copper concentrations in one river inhabited by Colorado pikeminnow were compared with effective concentrations estimated by regression. Comparisons suggest that ambient copper concentrations may occasionally inhibit olfaction of wild fish. Keywords~Copper Colorado pikeminnow Olfaction ,l, INTRODUCTION The Colorado pikeminnow (Ptychocheilus lucius) is a large cyprinid endemic to the Colorado River Basin, USA [1]. His- torically, the Colorado pikeminnow was widespread in warm- water streams and rivers, but the species was listed as federally endangered in 1967 in response to declining populations [2]. The decline of Colorado pikeminnow is commonly attributed to interactions with introduced fishes, construction of dams, and habitat modification [3,4], but effects of chemical contam- inants are increasingly becoming a concern. An important el- ement of Colorado pikeminnow life history is that natural reproduction is preceded by spawning migrations that may exceed 100 km in length. The means of navigation used by Colorado pikeminnow during migration are unknown, but it has been proposed that olfaction is a critical component of the homing process [1]. Many contaminants are known to disrupt olfaction in fish. Short-term sublethal exposure to copper, lead, mercury, nickel, silver, zinc, extremes of pH, and naphthalene inhibit olfactory ability [5-9]. Olfactory receptors are not pro- tected from contaminant exposure by external membranes but come into direct contact with water-borne solutes. Toxic sub- stances may alter detection of olfactory cues through several modes of action, including damaging organelles and enzyme systems, direct interaction with membrane receptor sites, or masking biologically important chemical signals. The purpose of this investigation was to describe the effect of contaminant exposure on olfactory ability of Colorado pikeminnow. This objective was achieved by exposing Col- orado pikeminnow to sublethal concentrations of copper for 24 or 96 h and evaluating olfactory ability using a behavioral assay coupled with observations of olfactory structures using * To whom correspondence may be addressed (danb@lamar.colostate.edu). Contribution 117, Larval Fish Laboratory, Colorado State Uni- versity, Fort Collins, Colorado, USA. Behavioral assay Scanning electron microscopy scanning electron microscopy (SEM). Advantages of combin- ing the two techniques were that the behavioral assay required study fish to detect, process, and respond to stimuli in an ecologically relevant fashion, and SEM observations provided evidence of related structural changes of olfactory receptors. The behavioral assay used in this investigation measured a response known as fright reaction in Colorado pikeminnow. The fright reaction is a well-known response of Ostariophysan fishes to fright pheromone, which is released from specialized cells in the epidermis when mechanical damage occurs [10,11]. Fright pheromone is detected by olfaction [10,11]. Conse- quently, failure of metal-exposed fish to demonstrate a fright reaction in the presence of the pheromone was considered evidence of a copper-induced loss of olfactory ability. Re- sulting exposure-response relationships were compared with copper concentrations near a Colorado pikeminnow spawning site to evaluate potential for effects on wild fish. MATERIALS AND METHODS Experimental animals Colorado pikeminnow were obtained from Dexter National Fish Hatchery and Technology Center (Dexter, NM, USA). Fish were fed a mixture of live <24-h-old brine shrimp nauplii (Aquarium Products, Glen Burnie, MD, USA) and a com- mercially prepared flake diet (TetraMin@; TetraWerke, Melle, Germany) twice daily. Colorado pikeminnow were 185 d old (after hatching) when studies were started. Total length and wet weight ranged from 25 to 44 mm and 0.14 to 0.68 g, respecti vel y. Exposure conditions The 24- and 96-h exposures were conducted following pre- scribed methods for renewal-acute toxicity tests [12]. Six con- centrations were studied for the 24-h exposure (< 10, 16.6, 33.3,66.5, 133, and 266 ILg/L copper) and five concentrations 907