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Chemically Resistant Fish (Fundulus heteroclitus)

Our study aims to elucidate how emamectin benzoate (EMB), known in the aquaculture industry as SLICE TM , affects Fundulus heteroclitus in the presence of P-glycoprotein (P-gp) inhibitors.

Fundulus heteroclitus is a small bodied fish commonly known as the mummichog or killifish. This fish species is extremely resilient, being able to endure very low oxygen levels, very high carbon dioxide levels, extreme changes in salinity and temperature, as well as tolerance to chemical pollutants. F. heteroclitus is commonly found in Nova Scotia estuaries. The Killifish are a non-migratory species that is found along our coast all year long, where it mostly spends it's time burrowing in the mud for food and warmth. Studies have shown that contaminants accumulate in the sediment at much higher quantities than in the free flowing water. Therefore, if a measure of contaminant is present in a region where the mummichog is commonly found we can be sure that the fish have had exposure to that contaminant due to the nature of their behaviour. Hence, the killifish are reflective of an area and provide a good environmental and toxological model for research.

Emamectin benzoate (EMB) is the chemical name for SLICE TM . SLICE TM is an in feed additive that is used throughout Canada to control the fish parasites known as sea lice in aquaculture farms. SLICE TM is relatively new to the market and has been used in Canada for the past three years. Emamectin benzoate is a product that was developed to replace the chemically related veterinary anti-parasitic drug ivermectin which took 100 days or longer to withdraw from the fish making the fish less marketable. SLICE TM only takes 25 days to withdraw. The ability that the cells have to expel SLICE TM at a faster rate is a possible indication that it is a better P-gp substrate than ivermectin and hence, in the presence of P-gp inhibitors it will accumulate even faster.

Emamectin benzoate is transported out of the cells by proteins known as P-glycoproteins. P-glycoproteins (P-gp) are more commonly known as multi drug resistance (MDR's) proteins that are highly conserved among all species. These proteins sit in the membrane of cells and serve as an efflux pump to export deleterious chemicals out of cells. P-glycoproteins are expressed in two types of organs. Organs that serve a secretion and absorption purpose and organs that serve a barrier function. Hence, they are prevalent in the liver, gut and the blood-brain barrier where they prevent the penetration of substrates into the brain. They play a key role in helping organisms cope with highly toxic environments, they prevent accumulation of the toxin within the organism (Bard, 2002a). P-glycoprotein inhibitors are chemicals that inhibit P-gp activity and prevent it from transporting its normal chemical substrates out of the cell. These inhibitors occur naturally in the environment by toxic algal blooms and are also added to the surroundings by human activity such as sewage, industrial pollution and agriculture.

In broad terms, we aim to understand how this chemical, will affect our waters and the marine populations that inhabit them. Specifically we are studying the behaviour of these fish before and after exposure to the pesticide and in the presence and absence of P-gp inhibitors. The first treatment involves SLICE TM independently. The second involves SLICE TM with a P-glycoprotein inhibitor and a control is used to study the expected or normal behaviour in the absence of chemicals. The behaviour is studied using a behavioural assay involving a tap test and a choice test will be used to quantitatively evaluate the experimental and control fish.

Keren Menashe
Undergraduate Researcher