Abstract
BackgroundA prerequisite for long-term survival of populations under multi-stress conditions is their capacity to set up efficient adaptive strategies. However, changes in the activity of molecular biomarkers have been for decades considered as early signals of the deterioration of the fish health and evidence of stress-related adverse biological effects. The aim of this study was to show that such changes actually represent adaptive response of fish to chemical stress. Gene expression and enzyme activity level in liver and brain of specimens from two populations of Abramis brama from contrasted habitats (nature reserve and urban) were examined. Selected parameters included biomarkers of general stress, antioxidative defence, xenobiotic metabolism, endocrine disruption, glucose homeostasis, iron homeostasis, and neurotoxicity.ResultsExposure of A. brama population from urban area to chemical stress was confirmed by assessment of chronic toxic pressure at fish habitats using Toxic Unit approach. The most pronounced response to chemical stress is observed through the activation of antioxidative defence mechanisms in brain and liver at gene and enzyme activity level, high biotransformation capacity of liver, and activation of mechanisms that will meet energy demands and compensate for the metabolic costs of the response to toxicants (higher expression of genes related to glucose homeostasis in the exposed population). Higher hepatosomatic index in the exposed population implies liver hypertrophy due to increased functional load caused by pollution. Body condition factors indicate good overall condition of both fish populations and confirm high efficacy of mobilized adaptation mechanisms in the exposed population.ConclusionsThe study provided the first data on basal expression of a number of genes in A. brama, potentially valuable for biomonitoring studies in absence of clear pollution gradient and/or reference sites (conditions). The study highlights importance of newly identified roles of various genes and proteins, typically considered as biomarkers of effects, and shows that changes in these parameters do not necessarily indicate the deterioration of the fish health. Such changes should be considered as adaptive response to chemical stress, rather than direct proof of ecological impact of pollution in situ.
Highlights
A prerequisite for long-term survival of populations under multi-stress conditions is their capacity to set up efficient adaptive strategies
Chronic toxic pressure at A. brama habitats According to the results of the official monthly monitoring of priority substances, priority hazardous substances, river basin specific pollutants and selected pesticides in water ([19, 20], data given in Additional file 1: Tables S1 and S2) during 2017 and 2018 the chronic toxic pressure was higher in protected than in urban area, but the contribution of organic chemicals to the overall toxic pressure is almost negligible (Max SUM TUch org 0.03) along the whole river section of interest for this study (Table 2)
According to the more detailed chemical analyses (Additional file 1: Tables S1–S4) of water samples taken at protected area (Bogojevo) and in the urban area of city of Novi Sad in the frame of Joint Danube Survey 3 (JDS3) [21], chronic toxic pressure is up to 2.5 higher in urban area (SUM TUch 0.82 and 1.36 vs. 0.54), while chronic toxic pressure deriving from organic compounds is up to 3 times higher in urban area (SUM TUch org 0.65 and 1.21 vs. 0.41)
Summary
A prerequisite for long-term survival of populations under multi-stress conditions is their capacity to set up efficient adaptive strategies. In case of absorption through gills and skin, chemicals go directly into the bloodstream and to the most of the organs, while ingested chemicals first undergo initial intestinal metabolism, absorption and hepatic biotransformation [2] Once they enter the organism, chemicals or their biotransformation products induce plethora of responses on various levels of organization in almost all organ systems, often resulting in mild to severe adverse effects. Depending on the ability of species to cope with the chronic chemical stress, the overall responses might range from gradual population decline (sometimes resulting in species extinction) to the development of biochemical and physiological adaptations as mechanisms for successful maintenance of homeostasis in the polluted environment [3,4,5,6]
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