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

Abstract

A swim bladder tumor was detected in one scoliotic medaka aged 22 weeks. The tumor was located in the dorsal abdominal cavity, with maximum dimension of 1850 × 1500 µm. No swim bladder lumen was identified, and the region where the swim bladder lumen would have been located, was replaced with adipose tissues. The tumor was a non-invasive, expansile, and encapsulated solid mass with a few cysts, and comprised a homogenous population of well-differentiated, densely packed, gas glandular epithelium-like cells. The tumor mass was connected to a rete mirabile that showed a hyperplastic capillary plexus; however, the tumor cells did not invade the rete mirabile, thereby revealing that the tumor was an adenoma originating from the gas glandular epithelium of the swim bladder. Since proliferative lesions have been reported in some teleosts with skeletal deformations, including medaka, the occurrence of a spontaneous swim bladder tumor in teleosts is considered to be closely associated with various types of skeletal deformation, and spinal curvature in particular.

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 .…”

Failure to gulp surface air induces swim bladder adenomas in Japanese medaka (<i>Oryzias latipes</i>)

“…The incidence of spontaneous swim bladder tumors in medaka is known to be very low, at 0.02% (2/10,000) 7 . However, these tumors are more frequent in wavy or scoliotic medakas, according to our previous case reports 5 , 14 . The common histopathological change accompanied by the tumors in these spinal deformity medakas was swim bladder inflation failure.…”

“…In physoclistous fish and some types of physostomous fish, the filling and emptying of the gas bladder are respectively performed by a secretory and resorbing section 14 , 37 . In physoclistous fish, the secretory section is anatomically composed of the rete mirabile and the gas gland: the rete mirabile is a dense bundle of parallel arterial and venous capillaries arranged side by side, whereas the gas gland is composed of folded cuboidal or columnar epithelium.…”