Drunken Parasites: Morphological Distortions Associated with Chemical Fixatives in Two Monogenetic Flatworms
Abstract
Fixation is the first step in the identification of animal parasites: its primary purpose is to kill the parasite and prevent or delay decomposition via autolytic enzymes. In the lab, parasitologists typically use ethanol (primarily 70%), formalin, or combinations of the two (e.g. AFA: glacial acetic acid, formalin, and ethanol), but there is little consensus on which best preserves the morphological characters used for parasite identification. Furthermore, parasitologists working in the field and/or internationally are often constrained in their choice of fixative: for example, ethanol can be difficult to obtain in countries that prohibit the sale of alcohol. Instead, various ad hoc fixatives are substituted, including rubbing alcohol, vinegar, hand sanitizer, or commercially available spirits such as rum. Despite this widespread practice, the distortions of parasite anatomy associated with these unconventional fixatives have never been examined. Therefore, we assessed morphometric distortions associated with different fixatives in two monogenetic trematodes, Protomicrocotyle mirabilis and Cemocotyle noveboracensis. Parasites were recovered live from the gills of freshly-caught Crevalle Jacks (Caranx hippos) and fixed in 70% or 95% ethanol, AFA, glacial acetic acid, rum, hand sanitizer, or rubbing alcohol. Fixed parasites were mounted on slides and key morphometric measurements taken. The degree of distortion observed differed among fixatives. Parasites fixed in 95% ethanol were particularly distorted, and included morphometric changes in sclerotized structures (i.e. haptoral clamps) generally assumed to be resistant to distortion by fixation. These results suggest that the choice of fixative can have profound effects on the ability to correctly identify parasites.
Faculty Sponsors
Dr. Christopher Blanar
Project Type
Event
Location
Alvin Sherman Library
Start Date
4-6-2021 12:00 PM
End Date
4-9-2021 12:00 PM
Drunken Parasites: Morphological Distortions Associated with Chemical Fixatives in Two Monogenetic Flatworms
Alvin Sherman Library
Fixation is the first step in the identification of animal parasites: its primary purpose is to kill the parasite and prevent or delay decomposition via autolytic enzymes. In the lab, parasitologists typically use ethanol (primarily 70%), formalin, or combinations of the two (e.g. AFA: glacial acetic acid, formalin, and ethanol), but there is little consensus on which best preserves the morphological characters used for parasite identification. Furthermore, parasitologists working in the field and/or internationally are often constrained in their choice of fixative: for example, ethanol can be difficult to obtain in countries that prohibit the sale of alcohol. Instead, various ad hoc fixatives are substituted, including rubbing alcohol, vinegar, hand sanitizer, or commercially available spirits such as rum. Despite this widespread practice, the distortions of parasite anatomy associated with these unconventional fixatives have never been examined. Therefore, we assessed morphometric distortions associated with different fixatives in two monogenetic trematodes, Protomicrocotyle mirabilis and Cemocotyle noveboracensis. Parasites were recovered live from the gills of freshly-caught Crevalle Jacks (Caranx hippos) and fixed in 70% or 95% ethanol, AFA, glacial acetic acid, rum, hand sanitizer, or rubbing alcohol. Fixed parasites were mounted on slides and key morphometric measurements taken. The degree of distortion observed differed among fixatives. Parasites fixed in 95% ethanol were particularly distorted, and included morphometric changes in sclerotized structures (i.e. haptoral clamps) generally assumed to be resistant to distortion by fixation. These results suggest that the choice of fixative can have profound effects on the ability to correctly identify parasites.
