Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Biology

Program Name/Specialization

Integrative Biology

Faculty/School

Faculty of Science

First Advisor

Mike Wilkie

Advisor Role

Supervisor

Abstract

The pesticides, 3-trifluoromethyl-4-nitrophenol (TFM) and niclosamide are used to control populations of invasive sea lamprey (Petromyzon marinus) in the Laurentian Great Lakes of North America. Added to streams infested with larval sea lamprey, the effectiveness of these pesticides, commonly called lampricides, are strongly influenced by water pH, with greater toxicity for both TFM and niclosamide in lower pH than higher pH water. However, the TFM and niclosamide sensitivity of sea lamprey are also greater in poorly buffered, low alkalinity water than in high alkalinity water but it is unclear why. One goal of my thesis was to propose a model that explained why TFM and niclosamide toxicity to larval sea lamprey was greater in lower versus higher alkalinity water. Based on toxicity tests , the model proposed contends that at low alkalinity there is greater acidification of the gill boundary layer water due to CO2 and H+ excretion by the larval sea lamprey as they breathe. The acidification increases the bioavailability of TFM and niclosamide at the gill surface, increasing their sensitivity to the lampricides. Another goal of my thesis was to determine if changes in gill function also contributed to the sea lamprey’s greater sensitivity to lampricides in low versus high alkalinity water. To examine this possibility, total ATPase and Na+/K+-ATPase activity in the gills, and plasma ion concentrations (Na+, Cl- ) were measured in larval sea lamprey exposed to TFM (3.5 mg L-1) alone, a TFM/1 % niclosamide mixture (2.9 mg L-1/ 29 µg L-1) or niclosamide alone (78 µg L-1) in waters of low (~50 mg L-1 as CaCO3), moderate (~150 mg L-1 as CaCO3) and high alkalinity (~250 mg L-1 as CaCO3), at a common water pH of ~ 8.3. At low and moderate alkalinity, total ATPase activity decreased with exposure to TFM and TFM/1 % niclosamide, but Na+/K+-ATPase activity was unimpaired. Blood plasma Na+ and Cl- concentration were not compromised following exposure to TFM, TFM/1 % niclosamide or niclosamide alone at low, moderate or high alkalinity. I conclude that any disturbances to gill function caused by exposure to lampricides, regardless of alkalinity, are insufficient to cause severe reductions in plasma Na+ or Cl- balance in larval sea lamprey. Instead, I propose that the greater sensitivity of sea lamprey to lampricides in waters of lower alkalinity is primarily a function of greater lampricide bioavailability in the gill boundary layers due to increased acidification of the water crossing the gills compared to higher alkalinities.

Convocation Year

2023

Convocation Season

Spring

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