Abstract
The remarkable and progressive “hepatic monolocular cystoadenoma” found in a four year old rainbow trout (Ω) was observed and described in this paper. The fish was reared in the fish-pond, the Agano River Fish Hatchery attached to the Fishery Experiment Station of Niigata Prefecture.
The coloration of the greater part of liver is milk white owing to the tumor. The liver of fish is transformed into a large empty ball, and its cystic space is filled with clear liquid. The wall of cyst consists of four layers: the fibro connective tissue, remaining liver cells, fibro connective tissue, and colloid layers, in order beginning at the outermost layer. In the interiormost layer there were some papilloma or knobs. Consequently, the present hepatic tumor has no layer of endothelium, while the marked hyperplasia of the connective tissue layer was found.
The columnar epithelium of gall-bladder was absent, however the abnormality was not recognized in the oesophagus, stomach, and spleen.
