RESUMO
The effects of ammonia and urea on branchial carbonic anhydrase (CA) enzyme which plays a key role in ionoregulation, osmoregulation and acid-base balance of rainbow trout (Oncorhynchus mykiss) were investigated. CA activity of the control group for ammonia and urea was determined as 1285.7 ± 67.9 and 1261.7 ± 60.8EU/mg protein, respectively. The CA enzyme activities of the other groups were measured at 1, 2 and 3h after ammonia and urea applications. The corresponding activities of ammonia were 774.9 ± 68.8, 732.1 ± 48.6 and 768.1 ± 59.5EU/mg protein, respectively and that of urea were 769.3 ± 58.9, 638.2 ± 47.7 and 1108.1 ± 61.1EU/mg protein, respectively. The differences between the initial CA activities for the controls was not significantly (P > 0.01). The CA activities were significantly (P < 0.01) inhibited both in ammonia and urea group. However, the ammonia inhibited more than urea since there was significant differences between final values of gill CA activities.
