Milda Zita Vosylienė

Studies of the acute and long-term toxicity of a heavy metal model mixture (HMMM) (based on real metal concentrations and proportion in soil near the Vilnius–Kaunas–Klaipėda highway on rainbow trout were performed using a set of biological parameters. The concentration of HMMM solution considered to be equal to 100% was for Cu 0.874; Zn 0.93; Pb 4.7; Ni 0.66; Cr 0.33; Mn 18 mg/l. The calculated 48-hour LC50 value for rainbow trout juveniles comprised 129.7%, and the 96-hour LC50 value 108.97% of HMMM solution. No significant changes were found in the weight of HMMM-exposed fish, while the liver weight of fish exposed to 21.79% of HMMM solution and the hepato-somatic index of fish exposed to 21.79 and 10.89% of HMMM solution differed significantly from control. Changes in blood parameters (erythrocyte count, haematocrit level, leukocyte count) revealed a specific HMMM toxicity to fish. Erythrocyte count decreased in the blood of fish exposed to all HMMM concentrations studied. Our data suggest that even low amounts of traffic emission pollutants can negatively affect the fish organism, causing various disturbances in its health and wellbeing.

This article is a survey of our works and works carried out by other authors dealing with the haematological indices of fish and their changes caused by heavy metals and their mixtures. The changes in these indices and their peculiarities depending on the concentrations of heavy metals and duration of exposure of fish to them as well as their physiological and ecological significance are discussed.

The aim of the study was to evaluate the toxicity and genotoxicity of heavy metals (HM) (Cu and Zn) and their mixture to rainbow trout (Oncorhynchus mykiss). No significant alterations in the erythrocyte count and haemoglobin concentration were found after exposure to Cu, Zn and their mixture at all three concentrations studied. The most significant decrease (P < 0.001) in leukocyte count was determined in the blood of fish exposed to 0.25 LC50 of HM and their mixture, 0.125 and 0.0625 LC50 of HM mixtures. A slight, but significant increase (P < 0.05) in hematocrit level was found in the blood of fish exposed to a 0.125 LC50 concentration of Cu and HM mixture. The frequency of micronucleated erythrocytes (MNE) increased after exposure to HM and their mixture at all three concentrations studied (0.25, 0.125 and 0.06 LC 50) (P < 0.0001), but there were no significant differences in MNE levels among the concentrations studied (P = 0.136). After a 96-hour recovery (in clean water) of the fish exposed to a HM mixture, the levels of MNE significantly decreased at the highest and lowest concentrations studied (P = 0.0001 and P = 0.004, respectively).

The effect of short-term (10-day) exposure of rainbow trout (Oncorhynchus mykiss) to stimuli of different origin (natural — starvation and anthropogenic — chemicals, i. e. heavy metal mixture) as well as to their combined action on their behavioural reactions, morphological parameters and physiological indices was studied and evaluated. Both stimuli induced changes of different degrees in the studied parameters. Starvation induced more expressed changes in morphological indices (decrease in fish condition factor, tissue weight); chemicals induced changes in physiological parameters (decrease in the fish ventilation frequency, increase in “coughing” rate, erythrocyte count, and haemoglobin). Combined effects of two stimuli evoked more significant alterations in the majority of studied parameters (tissue-somatic indices, cardio-respiratory and haematological parameters). Our data suggest that joint action of the two stimuli even of low intensity (concentrations of heavy metals in mixture were similar to concentrations found in unpolluted waters of Lithuania) can disturb the homeostasis of the fish organism.