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We present empirical support for a conceptual framework in which chemical contaminants are considered as sources of physiological stress to fish. Physiological stress was quantified in terms of energy by measuring routine metabolism, food consumption, activity, and growth rates of largemouth bass (Micropterus salmoides) exposed to the organochlorine pesticide dieldrin. Regression analysis was used to estimate models that describe the response of each endpoint as a function of dieldrin concentration and duration of exposure. Metabolic rate, consumption, and growth were influenced by chemical exposure. At short durations of exposure (1-4 days), metabolic rate of exposed fish was depressed compared with controls, but at a longer duration (16 days), metabolic rate increased as a function of concentration. Food consumption and growth rates of fish exposed for 16 days declined as dieldrin concentration increased. The response of each endpoint was consistent with predictions of the general adaptation syndrome. Energetic costs of contaminant-induced changes in metabolism and food consumption can be integrated with a bioenergetics model to demonstrate biological significance of chemical exposure in a natural environment. Résumé : Les auteurs présentent des données empiriques sous-tendant un cadre conceptuel selon lequel les contaminants chimiques constituent une source de stress physiologique pour les poissons. Pour quantifier la valeur énergétique du stress physiologique engendré par ces substances, ils ont mesuré le métabolisme normal, la consommation de nourriture, l'activité et les taux de croissance chez des achigans à grande bouche (Micropterus salmoides) exposés à la dieldrine, un insecticide organochloré. Au moyen d'analyses de régression, ils ont estimé des modèles décrivant les fluctuations de chaque paramètre en fonction de la concentration de dieldrine et de la durée d'exposition. La vitesse de métabolisme, la consommation de nourriture et la croissance variaient en fonction de la durée d'exposition. Le métabolisme des poissons exposés durant de courtes périodes (1-4 jours) était plus lent que celui des poissons témoins. En revanche, en cas d'exposition prolongée (16 jours), le métabolisme s'accélérait en fonction de la concentration de dieldrine, mais la consommation de nourriture et les taux de croissance diminuaient. L'évolution de chaque paramètre était compatible avec les caractéristiques d'un syndrome général d'adaptation. Le coût énergétique des changements intéressant le métabolisme et la consommation de nourriture induits par l'exposition au contaminant peuvent être intégrés dans un modèle bioénergétique pour démontrer le retentissement biologique de l'exposition à un contaminant chimique en milieu naturel.

Predation experiments, field studies, and individual-based-model (IBM) simulations revealed factors that affected the survival and recruitment of early life stages of endangered Colorado pikeminnow Ptychocheilus lucius in the Green River basin, Utah and Colorado. Small-bodied, nonnative red shiners Cyprinella lutrensis attacked Colorado pikeminnow larvae an average of once per minute, and predation success approached 30% in laboratory aquaria. Attack rate was also high in mesocosm experiments; turbidity and alternative prey reduced predation success. Distributions of hatching dates derived from otolith daily increment analysis showed that large cohorts of Colorado pikeminnow larvae that hatched in the Green River in early summer had low survival to autumn and that the few survivors were fast growing. Larvae hatched in midsummer or later had higher survival. Autumn juveniles grew 12-73% faster than summer juveniles, which suggested differential mortality of slow-growing fish. The IBM simulations integrated size-dependent predator-prey relationships, Colorado pikeminnow life history information, temperature-dependent pikeminnow growth, Green River predator size-structure dynamics, seasonally variable Green River water temperatures, and turbidity and alternative prey availability effects; the simulations showed that red shiner predation interacting with environmental variables may significantly reduce age-0 pikeminnow recruitment in autumn. Recruitment and growth patterns from simulations and field observations were consistent and suggested that the IBM is useful in evaluating management scenarios. Experiments, field studies, and predictive modeling provided consistent evidence that interacting effects of predation and environmental variables, including flow fluctuations, may structure intra-annual growth and recruitment patterns of age-0 Colorado pikeminnow. Flow management to benefit growth and survival of young pikeminnow, particularly early hatching ones, and reduced nonnative predator abundance in Green River backwaters may enhance the Colorado pikeminnow populations.

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 microg/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.

We present empirical support for a conceptual framework in which chemical contaminants are considered as sources of physiological stress to fish. Physiological stress was quantified in terms of energy by measuring routine metabolism, food consumption, activity, and growth rates of largemouth bass (Micropterus salmoides) exposed to the organochlorine pesticide dieldrin. Regression analysis was used to estimate models that describe the response of each endpoint as a function of dieldrin concentration and duration of exposure. Metabolic rate, consumption, and growth were influenced by chemical exposure. At short durations of exposure (1-4 days), metabolic rate of exposed fish was depressed compared with controls, but at a longer duration (16 days), metabolic rate increased as a function of concentration. Food consumption and growth rates of fish exposed for 16 days declined as dieldrin concentration increased. The response of each endpoint was consistent with predictions of the general adaptation syndrome. Energetic costs of contaminant-induced changes in metabolism and food consumption can be integrated with a bioenergetics model to demonstrate biological significance of chemical exposure in a natural environment.