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Considering that the excessive usage of vitamin E causes hypervitaminosis and thus reduces blood erythrocyte concentrations, therefore it is worth studying how its pharmacological dosage affects the activity of carbonic anhydrase (CA) enzyme found in erythrocytes of rainbow trout (Oncorhynchus mykiss) in vitro and in vivo. Vitamin E inhibited CA enzyme and the IC 50 value of the vitamin was 0.039 mM in vitro. Similarly, it was seen that vitamin E inhibited CA enzyme activity after the first hour following vitamin E injections in vivo. The activities of CA in groups of trout given vitamin E injection were measured at 1, 3 and 5 h and the corresponding activities were found to be 772.7 ± 290.5 (P < 0.05), 1286.4 ± 378.2 and 1005.7 ± 436.1 enzyme units (EU) g Hb -1 . The difference over the control was significant (P < 0.05) in the first hour and insignificant at 3 and 5 h (P > 0.05). The activity of CA in the control, which did not contain vitamin E, was determined as 1597.7 ± 429.0 EU g Hb -1 .

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The changes of copper, zinc, iron, magnesium, manganese, and triiodothyronine as a result of short- and long-term isothermal exposure to light were determined in the plasma of mirror carp (Cyprinus carpio). Two groups of fish were subject to a 3-mo treatment that consisted of (1) 8 h of light followed by 16 h of darkness and (2) 16 h of light followed by 8 h of darkness at 25 degrees C. No significant changes were recorded between the two groups at the beginning of the study. After 3 mo, the triiodothyronine and elements levels as well as the growth rates of fish in the long-time exposure period were significantly higher than those in the short-time exposure (p<0.05).