The Brown Fish Owl, Bubo zeylonensis or Ketupa zeylonensis, is an owl. This species is a part of the family known as typical owls, Strigidae, which contains most species of owl. The Brown Fish Owl and three related species were previously placed in the genus Ketupa; mtDNA cytochrome b sequence data is equivocal on which genus name is applied for this species (Olsen et al. 2002).

Foot showing adaptations to catch fish.

This is a large (55cm) owl. The upperparts are reddish brown, heavily streaked with black or dark brown. The underparts are buff with brown streaking. The throat is white. The eyes are yellow, and there are prominent "ears". Sexes are similar.

This species is a resident breeder in most of tropical south Asia from Pakistan, through India to south China; west of its main range, it is patchily distributed to the northern Levant. Its habitat is open wooded country, lowland forest and plantations, always near water.

In prehistoric times, this species was apparently present all over the central and eastern Mediterranean basin. These birds differed in size and have been separated as paleosubspecies B. z. lamarmorae (Dejaut, 1911). They are known from (probably) the Early Pliocene onwards (c.5 mya); at the onset of the last ice age, this population disappeared from the western part of its range, while the easternmost populations were probably subsumed in the gene pool of semenowi (Mlíkovský, 2003). The Late Miocene - Early Pliocene taxon "Strix" perpasta and the Late Pleistocene Bubo insularis are considered to be junior synonyms of the paleosubspecies by some (Mlíkovský, 2002).

It lays one or two eggs, often in the old stick nest of other birds, or in a rock crevice. Incubation is up to 38 days, and the young fledge after about 7 weeks.

This species is very nocturnal but it can often be located by the small birds that mob it while it is roosting in a tree. It feeds mainly on fish and frogs. Its calls are described as a deep "tu-hoo-hoo" or a soft huphuphuphuphuphup or a loud huhuhuhuhuhuhu.