Order : Perciformes
Family : ELEOTRIDAE
Species : Butis koilomatodon
Maximum Length : 10.7 cm

Butis koilomatodon (Crested Gudgeon, or Mud Sleeper) inhabits estuarine waters of varied salinity and varied substrate, including rocky substrate with crevices in which these fish can shelter. Its diet comprises crustaceans and small fishes (Fishbase).

This small gudgeon can be identified by its short, flattened head with a broad, dark bark at the rear of the skull. It is mottled brown, with pale specks, and vague oblique bands. The pectoral and anal fins may be pale-edged.

This species is wide-ranging; it naturally occurs from East Africa, through the Indian Ocean and Southeast Asia to China, the western Pacific Ocean and northern Australia. It has been accidentally introduced to other parts of the world including West Africa and South America.

It has been found in tide pools in Brazil (Bonfim et al, 2017). The ecological consequences of such introductions may result in native fish being outcompeted by the invader. Introduction has probably occurred due to international shipping activity; this hardy, adaptable fish may easily be transported in ballast tanks. 

Fig 1 : Example from Singapore, on a man-made, rocky bund at the edge of mangrove habitat on Pulau Semakau.

Fig 2 : Man-made granite bund and rocky foreshore, and newly planted mangrove on Pulau Semakau, Singapore, which support a population of Butis koilomatodon. The island is the site of Singapore's landfill facility, where incinerated refuse is buried.


References :

Larson, H.K. and Lim, K.P. 1997. A Guide to Gobies of Singapore. Singapore Science Centre.

Mariana Bonfim, Ana Paula Barbosa Martins, Glinia Kelle Fernandes Coelho de Carvalho, Nivaldo Magalhães Piorski & Jorge Luiz Silva Nunes (2017). Non-native mud sleeper Butis koilomatodon in Eastern Amazon Coastal region: an additional occurrence for the Brazilian coast and urgency for ecological assessment. BioInvasions Record, 6(2): 111-117.


Links :

Fishbase - Butis koilomatodon