Swim bladder tumors in the wavy medaka (<i>Oryzias latipes</i>)

Abstract

Swim bladder tumors were detected in three out of 28 wavy medakas aged about 2 years old, all of which displayed abnormal swimming patterns caused by their spinal curvature. The tumors were located in the dorsal abdominal cavity. The swim bladder lumen was not detected in the region where it was originally assumed to be located, and that region was replaced with adipose tissue. The tumors were non-invasive, expansile, and encapsulated solid masses composed of a homogenous population of well-differentiated, densely packed, gas glandular epithelium-like cells. The tumor masses were connected to the rete mirabile, but the tumor cells did not infiltrate into them. Histopathologically, these tumors were diagnosed as adenomas originating from the gas glandular epithelium of the swim bladder. Spontaneous swim bladder tumors are rare in medaka, with an incidence of 0.02%; however, in the present study of wavy medaka, the incidence was much higher (10.7%). The long-term physical effects on the gas gland caused by swim bladder deformation considered to be a secondary effect of the spinal curvature may be an important factor in the proliferation of the gas glandular epithelium in the wavy medaka, resulting in the higher incidence of swim bladder tumors.

Swim bladder tumor in the young adult scoliotic medaka (<i>Oryzias latipes</i>)

“…The morphology of swim bladder tumor in the present case was similar to that in the wavy medakas, described in our previous report 11 ; however, the rete mirabile was enlarged by the hyperplastic capillary plexus in this case. The proliferated rete mirabile in the swim bladder tumors was also detected in Sparus aurata 13 .…”

“…. In contrast, the incidence of swim bladder tumors is markedly higher at 10.7% (3/28) in wavy medakas11 . Additionally, it is reported that the juvenile fishes with skeletal deformations exhibit a high prevalence of spontaneous proliferative changes in the swim bladder, including the swim bladder tumors.…”

“…Spontaneous swim bladder tumors are rare, with an incidence of 0.02% (2/10,000) in medakas older than 24 weeks of age and 0.14% (7/5,000) in guppies older than 13 weeks of age that have been used in the control groups for various carcinogenicity tests 5 . In contrast, the incidence of swim bladder tumors is markedly higher at 10.7% (3/28) in wavy medakas 11 . Additionally, it is reported that the juvenile fishes with skeletal deformations exhibit a high prevalence of spontaneous proliferative changes in the swim bladder, including the swim bladder tumors.…”

“…Most swim bladder tumors are of the latter type and are diagnosed as adenomas, papillary adenomas, and/or adenocarcinomas. In our previous study, we reported swim bladder tumors in three wavy medakas 11 , which were characterized by kypholordosis 12 . In the present study, we encountered a swim bladder tumor in a young adult scoliotic medaka, which was characterized by sideways curved vertebrae, and described the detailed histopathological features of this tumor.…”

Spontaneous seminoma in medaka (<i>Oryzias latipes</i>)

“…In Case I, the medaka showed dorso-ventral curvature of its vertebral column, the so-called wavy medaka. In previous reports, the occurrence of a spontaneous swim bladder tumor in fish is considered to be closely associated with various types of skeletal deformation, and wavy medaka in particular 20,21 .…”