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|Title:||The ontogeny and mechanisms of branchial and cutaneous ammonia excretion in freshwater rainbow trout, Oncorhynchus mykiss|
|Abstract:||The mechanism by which freshwater fish excrete ammonia, the primary nitrogenous waste, has been a focus of comparative physiologists for nearly a century. The majority of ammonia in typical adult fish is excreted across the gill and is loosely coupled Na+/NH4+ exchange. However, few studies have addressed the mechanisms by which larval fish, lacking a functional gill, excrete ammonia. In the work presented in this thesis, cutaneous surfaces of post-hatch larval rainbow trout accounted for the majority of ammonia excretion (Jamm) and Na+ uptake (JNain), and both processes shifted to the gills at the exact same time over development (15 days post-hatch; dph), prior to the skin-to-gill shift in oxygen uptake (26 dph). Moreover, branchial Jamm and JNain¬ were tightly correlated over development (R2=0.95), while no such relationship existed at the skin. Moreover, experimental manipulation of Jamm and JNain demonstrated a lack of coupling of these processes by the yolk sac and body skin while branchial Jamm and JNain were functionally coupled to one another. Thus, Jamm by the gill of trout is a Na+-coupled process, while Jamm by the skin of larval trout is Na+-independent. Perhaps the most important finding of this thesis was that ammonia may play a role in driving the ontogeny of branchial ionoregulation. A new “ammonia hypothesis” was proposed, which is a refinement upon the current theory of gill development (the “ionoregulatory hypothesis”) and posits that Jamm, coordinated by Na+/NH4+ exchange, is the earliest function of the developing gill. Moreover, the demand for ammonia excretion may represent the primary driving force for the transition from cutaneous to branchial ionoregulation. Overall, this thesis extends the current knowledge of several aspects of ammonia excretion by freshwater fish, some of which had previously never been explored, and presents a number of new and exciting avenues for future research.|
|Appears in Collections:||Open Access Dissertations and Theses|
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|A.Zimmer-Biology PhD Thesis 2014.Defence Corrections.Final Version.pdf||Thesis||1.55 MB||Adobe PDF||View/Open|
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