06. Histological Characterization of the Freshwater Crustacean, Daphnia magnus

Abstract

With the growing concerns of pharmaceutical pollution entering our water systems, the freshwater crustacean Daphnia magnahas become a widely used animal model for studying the adverse effects of these contaminants. The crustacean’s high sensitivity to environmental changes make it an effective model organism in toxicological studies. While most invertebrates possess a neurogenic heart, D. magna is unique in having a myogenic heart which is also characteristic of vertebrates. As a result, these organisms exhibit similar cardiac muscle responses that can be compared to the vertebrate heart. Other notable features contributing to this organism’s usefulness in the field of ecotoxicology include a transparent exoskeleton, high fecundity, and a short generation time. Previous research on D. magna structure has focused on whole-mount histological proceduresthus potentially missing detailed microscopic anatomical features of the organism that might be impacted by these pharmaceuticals. The purpose of this study was to characterize the histological structure of D. magna. We accomplished this characterization using basic histological techniques: organisms were fixed using Bouin’s fixative, dehydrated in a series of graded alcohols, embedded in paraffin wax, sectioned at 10µm on a rotary microtome, gelatin-mounted on microscope slides, and stained with hematoxylin and eosin. Slides were then analyzed using photomicroscopy with a Moticam microscope and ImageJ software. This analysis of the microscopic anatomy of D. magna could lead to a better understanding of the ecological, physiological, and toxicological impacts of pharmaceutical contaminants on biological systems.