Master of Science (MSc)
Faculty of Science
Michael P. Wilkie
Sea lampreys (Petromyzon marinus) are a phylogenetically ancient jawless fish, with a multi-staged life cycle characterized by a prolonged suspension-feeding larval stage, which is followed by metamorphosis into parasitic lampreys that feed on the protein-rich blood of fishes. The switch from a nutrient poor to protein-rich diet in the sea lamprey is associated with an increased capacity to deaminate excess amino acids and to excrete ammonia and urea following metamorphosis. The focus of this thesis was to determine if changes in nitrogenous waste transporter protein abundance facilitate ammonia and urea excretion during different stages of the sea lamprey life cycle.
To investigate the mechanisms by which nitrogenous waste excretion (JN-waste) occurs in sea lampreys, individuals of various lifestages (larval/adults) were exposed to environmental stressors (highly alkaline water and high external ammonia) that have been previously shown to affect JN-waste in other fishes. Both ammocoete and adult sea lamprey were unable to tolerate highly alkaline (HA: pH= 9.5) water for more than 24 h. However, exposure of ammocoetes and adult lamprey to high external ammonia (HEA; 0.5 mmol*L-1 ammonia) resulted in the reversal of ammonia excretion (JAmm) and a net uptake of ammonia over 2 days. In adults, urea excretion (JUrea) increased significantly but remained unchanged in ammocoetes.
To determine whether there was a correlation between JN-waste patterns and the transport proteins associated with ammonia and urea excretion in sea lamprey, western blot analysis of Rh glycoproteins (Rhcg2) and urea transporters (UT) was performed on the main lifestages of sea lampreys (ammocoete, unfed parasitic, fed parasitic, adults) within gill and skin tissues. The abundances of Rhcg2 in the gill were significantly higher in fed parasites when compared to unfed juveniles and adult lamprey. Corresponding JAmm and plasma ammonia concentrations in these individuals were also greater. Larval sea lamprey UT protein abundances were significantly greater in gill tissues than in fed parasites and adult animals. This was postulated to be a function of the burrowing nature of the larval sea lampreys, and their relatively high rates of urea excretion compared to other life stages.
The period of metamorphosis was also accompanied by marked changes in body condition factor (CF), along with JAmm and JUrea, which were initially depressed during the mid-stages of metamorphosis before increasing several-fold near the completion of metamorphosis. Both Rhcg2 and UT expression in the gills peaked at stage 4 of metamorphosis and declined to young adulthood, whereas Rhcg2 and UT expression in the skin of metamorphosing animals was below detectable levels.
It is concluded that the changes in diet, along with habitat and activity level lead to the observed changes in the nitrogenous waste excretion patterns of the sea lamprey, which is reflected by corresponding changes in the abundance of the Rh and UT proteins. Further research into the regulation and localization of these proteins will prove useful in completing the picture of N-waste excretion in these phylogenetically ancient vertebrates.
Neal, James M. Mr., "Mechanisms of Nitrogenous Waste Excretion During the Complex Life Cycle of the Sea Lamprey (Petromyzon marinus)" (2013). Theses and Dissertations (Comprehensive). 1621.