<p> The origin of terrestrial vertebrates from water-dependent fish involved numerous
morphological and physiological modifications (Benton, 1990). Interest in the adaptive mechanisms involved in the transition from aquatic to terrestrial environments has led to
research involving lungfish. African lungfish are obligatory air breathers and have a primitive lung and characteristically underdeveloped gills compared to freshwater teleosts. The gills are thought to play an important role in CO2 excretion and possibly in water and ionic exchange while in aquatic conditions. At present, little is known about the basic ionoregulatory physiology of lungfishes; the aim of this thesis was to describe the basic principles of ion and water balance in two species of African lungfish, Protopterus dolloi and Protopterus annectens. Patterns and rates are very similar in the two species, apart from differences in water handling at the kidney. In aquatic conditions, plasma ion (Na+, Cl-, Ca2+) levels are lower than in teleost fish. The major site of diffusive water exchange appears to be the gills. The skin is well vascularized and also serves as site of water exchange, and likely Cl- and Ca2+ uptake as well. However, water and ion exchange rates are lower than in freshwater teleosts, probably due to the reduced gill area, though glomerular filtration, urine flow rates (an index of osmotic permeability), and urinary ion excretion rates are comparable to those of teleosts. Water exchange rates increase immediately after feeding, likely associated with specific
dynamic action, and decrease with prolonged terrestrialization, likely due to disturbances in gill function. A budget analysis of ion balance indicates that both unidirectional uptake from the water and net uptake from the food (especially for Cl-) are important, whereas unidirectional efflux across the gills and/or skin is a larger route of ion loss than are feces or urine. Despite many physiological differences between freshwater teleosts and the African lungfish, water and ion balance are maintained in a broadly similar fashion and are achieved by compensating for the reduced gill area by ion acquisition via the skin and by greater ion reabsorption by the kidneys.</p> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22388 |
| Date | 12 1900 |
| Creators | Patel, Monika |
| Contributors | Wood, C.M., Biology |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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