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A Study of Selenium Uptake in Parasite- Infected Rainbow Trout (Oncorhynchus Mykiss)

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A Study of Selenium Uptake in Parasite- Infected Rainbow Trout (Oncorhynchus Mykiss) View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of Saskatchewan's Research Archive PARASITES AND POLLUTION: A STUDY OF SELENIUM UPTAKE IN PARASITE- INFECTED RAINBOW TROUT (ONCORHYNCHUS MYKISS) A Thesis Submitted to the College of Graduate Studies and Research in Partial Fulfillment of the Requirements for the Degree of Masters of Science in the Toxicology Graduate Program University of Saskatchewan Saskatoon, SK, Canada Olesya Hursky ©Copyright Olesya Hursky, June, 2012. All rights reserved. PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a Postgraduate degree from the University of Saskatchewan, I agree that the Libraries of this University may make it freely available for inspection. I further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor or professors who supervise my thesis work or, in their absence, by the Head of the Department or the Dean of the College in which my thesis work was done. It is understood that any copying or publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Saskatchewan in any scholarly use which may be made of any material in my thesis. Requests for permission to copy or to make other use of material in this thesis in whole or part should be addressed to: Chair of the Toxicology Program Toxicology Centre University of Saskatchewan Saskatoon, Saskatchewan, S7N 5B3 i ABSTRACT Given that parasites demonstrate different sensitivity to contaminants and environmental stressors, there is an increasing interest in the use of parasites as biological or ecological indicators of their fish host life conditions as well as bioindicators of heavy metal pollution of aquatic ecosystems. In order to obtain insight into host-parasite relationships in selenium (Se) polluted environments, a study on nematode parasitism of rainbow trout exposed to subchronic dietary selenomethionine (Se-Met) was initiated. Se-Met is the major dietary form of selenium, and exposure to elevated dietary Se has been associated with detrimental effects on fish health and survival. In the current study, rainbow trout (Oncorhynchus mykiss) were experimentally infected with larval stages (L3) of the intestinal nematode Raphidascaris acus and subsequently exposed to an environmentally relevant concentraton of dietary Se-Met (4.54 mg/kg wet weight (WW)) for 70 days. The specific research objectives were to determine to what extent R. acus and its host accumulate Se from Se-Met fortified diet. In addition, non-specific biomarkers such as condition factor (K), hepatosomatic index (HSI), and gross energy (GE) were calculated to demonstrate the general effects of Se-Met exposure and parasitic infection on trout health. To further investigate joint effects of parasitism and Se-Met exposure on oxidative stress in rainbow trout, levels of superoxide dismutase (SOD) and gluthathione s-transferase (GST) were assessed in the liver and in the head kidney, as these enzymes are involved in the antioxidant response. Fish health variables, muscle Se concentration, and enzyme activity levels were compared between infected trout and uninfected fish exposed to same dietary Se-Met concentration for 56 days, as well as control fish. ii Subchronic exposure of uninfected rainbow trout to dietary Se-Met lead to an initial increase in muscle Se concentration reaching a plateau concentration at 5.27 mg Se/kg dry weight (DW), while a continuous increase in muscle Se was observed in infected trout exposed to Se-Met, reaching 7.52 mg Se/kg DW on day 70. Results suggest that continuous Se accumulation by parasitized fish could be due to increased susceptibility of rainbow trout to metal exposure as a result of infection with parasites. Furthermore, depletion in GE stores in infected rainbow trout exposed to Se-Met was observed (p<0.05), while no changes in K and HSI were detected between treatments, suggesting that challenging parasitic infection can significantly deplete energy reserves of the fish. In addition, in fish exposed to Se-Met an increase (p<0.05) in GST activity was recorded for the initial 7 days of Se exposure, whereas SOD activity was elevated (p<0.05) for the duration of the study. In contrast, fish exposed to both parasites and Se-Met showed a decrease (p<0.05) in antioxidant enzyme levels when compared to trout exposed to Se- Met alone, suggesting an important role of parasitic infection in suppressing oxidative stress response of the host. In summary, parasites such as R. acus can upregulate absorption of Se in the final host, leading to increased deposition of Se into the muscle tissue. In contrast to its host, R. acus did not accumulate large concentrations of Se (1.91 mg Se/ kg DW), and therefore may not be very useful as a biomarker of Se pollution. In addition, parasites negatively influenced expression of general oxidative stress biomarkers (SOD, GST) and therefore should be considered in ecotoxicological studies. To our knowledge, this is the first study to demonstrate effects of combined Se-Met exposure and parasitic infection on rainbow trout health and the oxidative stress response. iii ACKNOWLEDGEMENTS I would like to thank my supervisor Dr. Michael Pietrock for his patience, continual guidance and support, and for always being available when I needed help. Thank you to my advisory committee, Dr. Barry Blakley and Dr. Dave Janz along with my external examiner Dr. Emily Jenkins, for the time they contributed to my degree and thesis. A special thank you to Dr. Xiaofeng Wang, Dr. Lynn Weber, Dr. Som Niyogi, and Dr. Jason Raine for their assistance in the completion of my lab work and with the technical aspects of my research. I would also like to thank Michael Kautzman, Bryan Sarauer, Jith Thomas, Raymond Kwong, Larisa Matwee, JJ Kim, and Gary Sun for their help in the laboratory, and the Toxicology Centre’s staff and students for the support they have given as a student in the Toxicology Program. I would also like to acknowledge Noland Henderson and Montreal Lake Cree Nation for proving whitefish from the Montreal Lake, SK. I would not have been able to complete this journey through my degree in a balanced way without the support and patience from my family and friends. To my husband, Rostyk Hursky, thank you for listening and helping with all the little things that add up to a lot - without your love, patience, and support this would have been a very difficult journey. To my Mom, step-Dad, and sister, Ulyana and parents-in-law- thank you for your kind words and guidance and for always being there when I needed you- I hope I have made you proud. Last but definitely not least, thanks to all my wonderful friends from Saskatoon and Toronto for continual support and comical relief. iv TABLE OF CONTENTS PERMISSION TO USE ................................................................................................................. i ABSTRACT ................................................................................................................................... ii ACKNOWLEDGEMENTS ........................................................................................................ iv TABLE OF CONTENTS ............................................................................................................. v LIST OF TABLES ..................................................................................................................... viii LIST OF FIGURES ..................................................................................................................... ix LIST OF ABBREVIATIONS ...................................................................................................... x PREFACE .................................................................................................................................... xii 1.0 GENERAL INTRODUCTION ..................................................................................... 1 1.1 Selenium .......................................................................................................................... 1 1.1.1 Properties and sources ............................................................................................. 1 1.1.2 Toxicokinetics ........................................................................................................... 2 1.1.3 Deficiency ................................................................................................................. 4 1.1.4 Toxicity ...................................................................................................................... 5 1.1.5 Interactions with other metals .................................................................................. 9 1.1.6 Mechanisms of action and resistance ....................................................................... 9 1.2 Fish health parameters ................................................................................................ 13 1.2.1 Fulton’s condition factor ........................................................................................ 13 1.2.2 Hepatosomatic index ............................................................................................... 14 1.2.3 Gross energy ..........................................................................................................
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