The redfin bully (Gobiomorphus huttoni) is a species of freshwater fish in the family Eleotridae endemic to New Zealand.

Male redfin bullies are the most colourful freshwater fish in New Zealand, with bright red markings on the dorsal, anal, and tail fins, as well as the body and cheeks.

[5] During breeding the male fish turns a solid black colour with a bright green edge to the first dorsal fin.

[6] G. huttoni are considered to be cryptic fish, as their colouration enables them to camouflage and blend with their surroundings, which is an important defence mechanism.

[9] A research study by Vanderpham undertook a series of body and fin measurements, and cephalic dorsal head pores of the mechanosensory lateral-line system were counted on the G. huttoni.

G. huttoni are quite rare along the east coast of the South Island north of Oamaru, with the exception of the Banks Peninsula area.

[12] G. huttoni are typically found in habitats with cobbled bottoms, swift water flows and riffles from large rivers.

[13] The male changes colour, darkening from brown to completely black, to increasingly camouflage with its habitat while defending the nest.

[18] G. huttoni demonstrate a preference for habitat patches with both abundant food resources and a lower risk of predation.

[19] Male and female G. huttoni show differences in preferred habitat selection, specifically preceding or during breeding periods.

G. huttoni is an opportunistic feeder, eating the larvae of chironomid midges, mayflies, and caddisflies; small crustaceans; and aquatic snails.

[13] Female G. huttoni show a preference for Diptera (flies), Ephemeroptera (mayflies) and Amphipoda, with the variation in diet predominantly due to habitat difference, which mainly occurs during the breeding season.

The importance of Diptera as a food source remains high irrespective of the size of G. huttoni individuals, but their diet becomes more varied as they grow.

However, when G. huttoni reach adulthood at around two years they are able to reside upstream in freshwater habitats, then gaining access to different food sources.

[1] The following species have overlapping habitat ranges with G. huttoni; however, there has been limited research undertaken to date to fully understand the scale of the predator-prey relationship.

[21] The table below summarises some of the recent changes to the G. huttoni habitat that are threatening the species, and potential mitigants and management to reduce the ongoing environmental impact: If possible, expand width of riparian zones during later rotation planting.