Butis koilomatodon, commonly known as the mudsleeper, is a species of fish in the family Butidae native to fresh, brackish and salt water of the Indo-Pacific region, ranging from Madagascar and Mozambique to the Philippines, China and Australia. It has been introduced to the Atlantic region where considered invasive and known from Panama, Venezuela and Brazil as well as Nigeria. This predatory species mainly lives in rivers, estuaries and mangroves, and reaches up to 10.7 cm (4.2 in) in total length.