Bully (Redfin bully) Gobiomorphus huttoni
Species: G. huttoni
Binomial name: Gobiomorphus huttoni
Common name: Redfin bully
Gobiomorphus huttoni is a species of freshwater sleeper goby endemic to New Zealand and is found throughout New Zealand’s North and South islands, Stewart Island and the Chatham Islands.
Males have bright red markings on the dorsal, anal, and tail fins, as well as the body and cheeks. Additionally, males have a bluish-green stripe on the outer edge of the first dorsal fin. Only the males have the red colouring; the females have the same patterns, but with brown in place of red. G. huttoni of both sexes have distinctive diagonal stripes on their cheeks. These stripes are very useful for positive identification, as they are visible in small (about 30 mm long) and very pale fish. G. huttoni reaches a length of 80 -120 mm. Males are larger than females.
G. huttoni are diadromous and are in the anadromous category, which is when a fish is born in fresh water, spends some of its life in the sea and returns to fresh water to spawn. This diadromous habit means that they are widespread throughout the country in coastal areas. They do not establish land-locked populations.
Over winter and spring, the male establishes and defends a ‘nest’ – usually a hollow beneath a rock. The male turns very dark, from brown to completely black, while defending the nest. When a female is ready to lay eggs, she enters the nest and turns upside-down to lay 1,000–20,000 oval eggs in a close-packed, single layer attached to the nest’s ‘ceiling’. The male then fertilises the eggs. The female leaves the eggs in the care of the male, which guards them until they hatch two to four weeks later. Females may lay more than once over the spawning season, and one male may defend the eggs of more than one female. Upon hatching, the 3 mm fry are carried downstream to the sea; several months later, they return as 15–20 mm juveniles, and live the rest of their lives in fresh water. They reach sexual maturity in their second year and have an average lifespan around 3–4 years.
G. huttoni juveniles are very good climbers, able to traverse waterfalls with populations recorded above 5-m-high waterfalls.
G. huttoni mainly live in the runs and pools of small, boulder-filled streams, and prefer a habitat with a moderate flow of water with pools and riffles (a shallow section of a stream or river with rapid current), in quite large gravely streams with cobble substrates. They do not need a dense overhead canopy, but prefer a high proportion of native trees. They are opportunistic feeders, eating the larvae of chironomid midges, mayflies, and caddisflies, small crustaceans, and aquatic snails.
The main threats to G. huttoni are competition and predation from introduced salmonid fishes, mainly brown trout (Salmo trutta), and habitat loss. Over the last 10 years, redfin bully numbers have declined by 20%, and they are now classified as a near-threatened species.
An adult redfin bully
Two juvenile G. huttoni