Fixation Artifacts in Rainbow Trout (Salmo gairdneri) Gills: A Morphometric Evaluation

Epithelial capillary separation (E.C.S.) and epithelial cell hypertrophy (E.H.) of the gill lamellae of fish are two histopathological changes frequently described in association with toxic insults. Both of these gill changes increased in a significant linear manner over delay periods of 20–900 s from death to first entering either Bouin's or 10% formalin fixative. E.C.S. also occurred rapidly when gills were examined as whole mount preparations. The presence of occasional necrotic epithelial and chloride cells resembled apoptosis and is not in itself abnormal, nor did the type of fixative used or fixation delay have an effect on their extent. Gills from fish killed by either MS-222 or cervical spinal severance were similar, except that the latter also had multifocal lamellar telangiectasis. We conclude that E.C.S. and E.H. are readily mimicked by preparation and postmortem artifacts that occur rapidly after death when this is caused by either MS-222 or spinal severance. Bouin's fixative should be used to minimize these changes.