The occurrence, chemical and crystallographic nature of the calculi, and their effects on the survivorship of larvae of Japanese flounder were investigated.
Two types of calculi were distinguishied as to their colors and localities; most of calculi were a milk-white one found exclusively in the urinary bladder. Orange calculi, while comparatively few in number, were in both the kidney and the urinary bladder. Both types of calculi were mainly composed of calcium phosphate in amorphous forms, but the elements of each calculus was different. Calcium and phosphorus were detected in the milk-white calculi, while sulphur in addition to calciumand phosphorus were in orange calculi. The bladders containing milk-white calculi showed no histological changes in the kidney, but when orange calculi was observed in a proximal segment or a collecting tubule of the kidney, the lumen was abnormally expanded and the epithelium cells were flattened. But calculi-holding larvae did not show a specifically higher mortality compared to normal larvae.
