Effect of buffers on the gill structure of common carp, Cyprinus carpio L., and rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract. The effects of phosphate and tris buffers on the gill structure of common carp, Cyprinus carpio L, and rainbow trout, Oncorhynchus mykiss (Walbaum), were investigated. Common carp maintained in phosphate-buffered (a combination of sodium di-hydrogen phosphate and di-sodium hydrogen phosphate at a final concentration of 0.01 m ) standard dilution water for a period of 8 days developed severe pathological changes in the gill tissues, while carp maintained in tris-buffered (0.01 m ) dilution water and trout subjected to either of these buffers showed no such changes. Histological changes in the gills of carp exposed to phosphate buffered dilution water included an extensive mucous cell proliferation on the lamellar and filarnental epithelium, and an increased infiltration of eosinophilic granular cells into the gill tissues. A moderate epithelial hyperplasia and an increase in the chloride cell densities on the gill epithelia were also noted. The implications of these findings on the widely accepted practice of the use of phosphate salts and various other buffers in pH control of experimental water are highlighted.