Modifications of acute physiological stress response in whitefish after prolonged exposures to water of anthropogenically impaired quality

Abstract

Hatchery-reared, 1⁺- and 2⁺-year-old juvenile European whitefish, Coregonus lavaretus, were exposed to two kinds of anthropogenic waste waters, bleached kraft mill effluents (BKME) and iron supplemented peat water in altogether five laboratory and field experiments. Besides the traditional "expose and execute" - method that addresses merely momentary effects of impaired water qualities on aquatic animals, the main target of the study was set to reveal possible functional alterations in the acute physiological stress response of exposed fish. Therefore, some of the fish were after each exposure period (21 - 42 days) subjected to a short stressful handling disturbance and, after precisely defined recovery periods (5 min - 5 h), sampled similarly to the fish sacrificed before the additional handling procedure. A complementary experiment was carried out to merge some of the effects of previous waterborne exposures with those originating from the oral administrations of iron overdose and dehydroabietic acid, obviously the most hazardous agents involved in the previous studies. Moreover, to ascertain the reliability of the field results and to compare the impacts of a natural factor to those derived from the anthropogenic water quality impairment, the effects of four different acclimation temperatures were studied within two experiments. In accordance with the integrated nature of the general stress response, a wide variety of end points, both at the primary and the secondary levels of physiological responses were applied. The results indicate the following points: 1) Due to the time-dependency and sensitivity of the physiological stress response, the evaluation of recovery periods is overwhelming for the reliability of the method. 2) Both the primary and the secondary level of the integrated stress response may be modified by the applied impaired water quality regimes. 3) Deviations in the characteristics of the secondary stress response between different experiments are generally smaller in unexposed than in exposed fish. Thus, the nature of responses, and the reliability of the results therein, may be more precisely predicted in fish maintained in uncontaminated water quality. 4) In whitefish maintained in dechlorinated tap water, the physiological stress response is influenced by acclimation temperature, whereas after a subchronic exposure to impaired water quality, the effects of ambient conditions in whitefish disappear to a great extent. 5) The interpretation of data may be easily confused due to a capture of freely swimming fish. To obtain reliable and comparable results in field studies, the sampling method should be either fast or time-dependently standardised. 6) The paucity of the reports considering methodological aspects of this kind together with the widely accepted employment of stressful catching methods involving a delayed sampling of wild fish, suggests ignorance associated with ecotoxicological studies.