engleski

Assessment of general condition of fish inhabiting moderately contaminated aquatic environment

In September 2009, the upper flow of the Sutla River (Croatia) was characterized by low dissolved oxygen level and increased number of heterotrophic bacteria in the water, as a probable sign of diffuse organic enrichment of the river water, with additional faecal and inorganic water contamination at one restricted river section. However, total dissolved concentrations of each trace element individually still have not exceeded the limits considered as hazardous for the aquatic life, and both faecal and organic pollution at the majority of the sampling sites could be considered as moderate. The aim of this study was to examine if multiple disturbances in the aquatic ecosystem, although only moderate, could cause increased stress in fish when they occur concurrently, and if they consequently could result in some changes in fish condition and health. Selected fish species was European chub (Squalius cephalus L.), caught at two sites within the contaminated upper river flow (30 specimens) and at three sites at downstream river section (45 specimens). The condition indices of chub from upper river section were lower compared to downstream sites, whereas gonadosomatic indices exhibited opposite trend with the highest values obtained at the most upstream site. Additionally, hepatosomatic indices were increased at metal-contaminated site 2. Metallothioneins, inducible metal-binding proteins, were measured in the chub liver and gills, as biomarkers of metal exposure. However, their slight increase was recorded at both upstream sites and not only at metal-contaminated site 2, rather as a sign of general stress than as the consequence of increased metal accumulation. The incidence of the bacterial and parasitic infections in the chub tissues also had characteristic spatial pattern. Therefore, fish health should be regularly monitored even in moderately contaminated aquatic environment to prevent more serious deterioration of fish condition in the case of long lasting unfavourable living conditions.

bacterial and parasitic infections ; condition index ; European chub ; gonadosomatic index ; hepatosomatic index ; metallothionein ; Sutla River

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