10 Ultrastructural and Morphometric Studies on Ion and Acid-Base Transport Processes in Freshwater Fish

Publisher This chapter presents ultrastructural and morphometric studies on ion and acid–base transport processes in freshwater fish. The freshwater fish gill shares a number of common functional and morphological features with some well-characterized epithelial surfaces, including the frog skin, the toad and turtle urinary bladder, and the cortical collecting duct of the mammalian kidney. The response of the trout gill to intravascular infusion of acid is inconsistent with the morphological model for acid-–base regulation. Continuous infusion of HCl produces an unexpected 135% rise in the chloride cell fractional area in the rainbow trout. The importance of variations in gill morphology in response to an exposure to variation in environmental pH has received a great deal of attention. An exposure to low or high pH results in changes in the driving gradients for acidic and basic equivalents. During an exposure to low environmental pH, there is an increase in the electrochemical gradients favoring net retention/gain of acidic equivalents and a net loss of basic equivalents from the fish. It has been found that there are discrete inter- and intraspecific differences in the appearance of the chloride cell (CC) among species and their responsiveness to variation in acid–base status.