Clarias batu is a species of clariid catfish

Catfish

Catfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...

. It is only known from Tioman Island

Tioman Island

Tioman Island is a small island located 32 km off the east coast of Peninsular Malaysia in the state of Pahang, and is some 39 km long and 12 km wide. It has eight main villages, the largest and most populous being Kampung Tekek in the north...

 off the eastern coast of Peninsular Malaysia

Peninsular Malaysia

Peninsular Malaysia , also known as West Malaysia , is the part of Malaysia which lies on the Malay Peninsula. Its area is . It shares a land border with Thailand in the north. To the south is the island of Singapore. Across the Strait of Malacca to the west lies the island of Sumatra...

. The eel

Eel

Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...

-like catfish found on this island were originally identified as the widespread species Clarias nieuhofii

Clarias nieuhofii

Clarias nieuhofii is a species of clariid catfish. It has a wide distribution in Southeast Asia including peninsular Malaysia, Java, Sumatra, Borneo and the Philippines....

but comparison of a large series of specimens from Tioman with a series of C. nieuhofii from the mainland revealed consistent and distinctive differences indicating a separate species.

This is an elongated catfish up to 30 cm standard length

Fish measurement

Fish measurement refers to the measuring of the length of individual fish and of various parts of their anatomy. These data are used in many areas of ichthyology, including taxonomy and fisheries biology.-Overall length:...

. It can most readily be distinguished from C. nieuhofii by the fact that the dorsal

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

 and anal fins are clearly separated from the caudal fin whereas C. nieuhofii has all these fins confluent. Care should be taken however as specimens of C. batu have been recorded which have apparently confluent fins as a result of healing after suffering damage.