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Tolerance of Nile tilapia to nitrites
BROŽ, Pavel
The aim of this thesis was to evaluate the effect of increased concentrations of nitrite to Nile tilapia (Oreochromis niloticus) at different concentrations of chloride. Tilapias adults were exposed for 14 days to nitrite at the concentration of 3 mg.l?1 NO2? (i.e. concentration commonly found in recirculation systems). After 14 days the experimental fishes were divided into 4 group, which differed in concentrations of nitrite and chloride. These groups of fish were held in different conditions for the next seven days. Using standard clinical procedures the following haematologic biochemical parameters were determined: RBC, WBC, Hb, PCV, MetHb, MCV, MCH, MCHC, NO2-, GLU, Ca, Mg, TP, NH3. The tested nitrite concentration was not high enough to cause strong differences of pursued parameters. Only some of them (Hb, MetHb, MCHC) were statistically significant.
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Changes of biochemical parameters in fish after nitrite exposure
PODLESNÝ, Martin
The aim of this thesis was to assess the effects of long-term nitrite exposure on mortality, growth rate and blood biochemistry in rainbow trout (Oncorhynchus mykiss). Furthermore, acute toxicity tests with nitrite were performed on rainbow trout (Oncorhynchus mykiss) and sheatfish (Silurus glanis). The theoretical part focuses on aquatic toxicology including toxicity evaluation of substances and preparations for water organisms. Detailed information on nitrite are summarized there, namely information on nitrite occurrence and sources in aquatic environment and the mechanism of their uptake and toxic influence on fish including factors influencing their toxicity. The practical part consists of methodology and results of acute toxicity tests on rainbow trout and sheatfish and sub-chronic test on rainbow trout. According to the acute toxicity tests results, 96hLC50 values were estimated at 11.2 mg.l-1 NO2- for rainbow trout and 15.3 mg.l-1 NO2- for sheatfish. Sub-chronic exposure of rainbow trout to nitrite concentrations ranging from 0.01 to 3.0 mg.l-1 lasting 28 days caused an increase of glucose concentration and a decrease of potassium concentration in the blood plasma among all experimental fish compared to control. Elevated nitrite levels were found in the plasma of the fish exposed to concentrations of 0.6 mg.l-1 NO2- and greater. The plasma nitrite levels did not reach those applied in any experimental group in the present study. At highest nitrite concentration (3.0 mg.l-1 NO2-), 42 % growth inhibition and 65 % mortality among fish was noticed. On the basis of growth rate inhibition data, the values of NOEC and LOEC were estimated at 0.01 mg.l-1 and 0.2 mg.l-1 NO2-, respectively.
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