Ultraviolet radiation is an ecological factor that directly affects terrestrial organisms through suppression
of immunity or damage to internal organs. The present study assessed the effects of ultraviolet A (UVA)
radiation on the kidneys of both wild-type (WT) and p53-deficient medaka (Oryzias latipes) and evaluated
which strain was more resistant to the effects of UVA. Fish were divided into four groups: control group 1
(Cwt and Cp53), kept for 3 days without UVA exposure; group 2 (1wt and 1p53), fish exposed daily to UVA
for 1 h day−1 for 3 days; group 3 (2wt and 2p53), fish exposed daily to UVA for 2 h day−1 for 3 days; and
group 4 (3wt and 3p53), fish exposed daily to UVA for 3 h day−1 for 3 days. Samples of tissues were
obtained 24 h after UVA exposure. The most obvious histopathological changes induced by UVA radiation
in kidney tissues of both strains of medaka (WT and p53-deficient) were high levels of vacuolation of
tubular cells followed by necrosis. The tubular segments lost their normal shape which appeared like a
network structure and their cells with clear cytoplasm. Necrosis of lymphoid tissues and spots of brown
pigmentation (possibly melanomacrophages) were sporadically seen in interstitial lymphoid tissues, while
shrinkage of glomeruli, diminution of periodic acid–Schiff staining, and increased amount of collagenous
fibers were observed. Our results confirmed the harmful effects of UVA radiation on kidney tissues of both
WT and p53-deficient medaka. However, WT medaka was affected more than p53-deficient medaka.