UBC Theses and Dissertations
Functional aspects of the osmorespiratory compromise in fishes Mussoi Giacomin, Marina
The fish gill is a multipurpose organ that plays a central role in gas exchange, ion regulation, acid-base balance and nitrogenous waste excretion. Effective gas transfer requires a large surface area and thin water-to-blood diffusion distance, but such structures also promote diffusive ion and water movements between blood and water that challenge the maintenance of hydromineral balance. Therefore, a functional conflict exists between gas exchange and ionic and osmotic regulation at the gill. The overarching goal of my thesis was to examine the trade-offs associated with the optimization of these different functions (i.e. the osmorespiratory compromise) in species with diverse osmoregulatory strategies, when exposed to environmental stressors such as hypoxia, changes in temperature and salinity. To address this I have used three species of fish that are phylogenetically, ecologically and physiologically diverse, the Atlantic killifish (teleost), the Pacific hagfish (myxine) and the Pacific spiny dogfish (elasmobranch). My results show that salinity influences the capacity to regulate oxygen consumption at low oxygen and hypoxia tolerance in the killifish. Acclimation to fresh water resulted in a lowering of the lamellar respiratory surface area and a higher percentage of the gill lamellae covered by an interlamellar cell mass. These responses could be adaptations to aid survival in hypo-osmotic waters as freshwater-acclimated fish showed a greater ability to downregulate transcellular gill permeability to both ions and water when exposed to hypoxia in comparison to their seawater-acclimated counterparts. However, at salinities ranging from fresh water to 100% sea water, plasma ion concentration and osmolality were unaffected by hypoxia. I also found that there is a strong interaction between gill permeability to gases and to ions and water in hagfish, an osmoconforming marine species in which the osmorespiratory compromise had never been investigated. An increase in gill permeability to urea, ammonia, and water was also seen in the dogfish exposed to elevated temperature, indicating a disruption in the nitrogen conservation mechanisms at the gill. In summary, this thesis has expanded the range of species in which the osmorespiratory compromise has been investigated, and has provided new insights into the mechanisms involved.
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