Thesis Info

Thesis Title
Francisco Ucan-Marin
2nd Author
3rd Author
Master in Science
Number of Pages
Dalhousie University
Thesis Supervisor
Ron O' Dor
Supervisor e-mail
odor AT
Other Supervisor(s)
Language(s) of Thesis
Department / Discipline
Biology / Ecotoxicology
Languages Familiar to Author
English, Spanish & Mayan
URL where full thesis can be found
Ivermectin, Endocrine disrupters, Salmo salar, Vitellogenin, Cholinesterase
Abstract: 200-500 words
Ivermectin (Eqvalan) has been used as an oral treatment against sea lice (Lepeophtheirus salmonis) infestations on farmed salmon (Salmo salar L.) in Chile, Ireland, Canada, United Kingdom and recently it has been considered for control of parasite copepods on cultured sea bass (Dicentrarchus labrax) in the mediterranean region. The application of Ivermectin can damage the nervous system of invertebrates, and has been shown to inhinibit the respirationof rainbow trout (Toveey, et al 1999). Ivermectin has been also founded in the central nervous system, showing than ivermectin is able to pass the blood-brain barrier (Hoy et al.,1990; Katharios et al., 2003). One hundred and twenty fish were randomly distributed in two different treatments of ivermectin, in the diet: 0.05 and 0.25 mg kg-1. Over 30 days fish were dosed every third day, for a total of ten doses. Fish feeding behavior and swimming rates were observed and recorded. After 30 days treatmnent period 10 fish form each tank were sacrified and samples of plasma blood, head, liver and gonads were taken. After 30 days treatment period, the reamining fish were held an additional 30 days, during which time they were fed a clean diet and their behavoiur was observed. At the end of that period there were sampled in the same way as after the initial exposure period. Analysis of brain acetylcholinesterase activity were performed at the laboratories of Veterinary College, of Prince Edward Island. The author of this thesis performed enzyme-linked immunoabsorbent assay (ELISA) to determine Vg concentrations at the laboratories of the National Research Water Institute in Burlington ON. Ivermectin treatment increased brain acetylcholinesterase activity and decreased movement and feeding activity of fish. Ivermectin in this study appears to be a neuroexcitatory pesticide that is responsible for disrupting the normal BAChE activity of Atlantic salmon. The lethal concentrations of ivermectin in food were calculated to be 0.174 mg kg-1. Although there were significant [ANOVA, (p<0.05)] decreases in vitellogenin levels of treated fish compared with controls, ivermectin was not judged to be and endocrine disrupters as those changes were not large. Liver somatic index (LSI) was the most notable and significant effect [ANOVA, (p<0.05)] comparing fish treated with ivermectin with control group. Fish dosed 0.05 mg kg-1 for 30 days and fed with commercial diet for 30 days had 49% lower LSI than control fish. Ivermectin exposure affected fish through paralysis, lethargy and possible ataxia. Also, fish treated present less weight-length values compared with fish control group. With the data obtained in this study I conclude that ivermectin induces significant differences in vitellogenin activity, liver somatic index and weight-length between fish treated and fish control group [ANOVA (p<0.05)]. Studies evaluating the recovery of brain acetylcholinesterase and vitellogenin activity in long-term studies are necessary to approach a better understanding of ivermectin in its role as neurotoxic compound and as possible endocrine disrupter.