Bullies (Fish)

Bullies are fish found in the tropical waters of the Pacific and South-East Asia belonging to the family Eleotridae, also known as 'sleeper gobies'. The name most commonly refers to the genus Gobiomorphus, particularly the seven species endemic to New Zealand: bluegill, common, Cran's, giant, redfin, Tarndale and upland. Bullies make up the second-largest family of native freshwater fish in New Zealand.

Bullies live in streams, rivers and lakes throughout New Zealand. Some species are diadromous, migrating between fresh and salt waters, while others live only in freshwater. Bullies are generally small fish, ranging from 5 centimetres to over 15 centimetres. Many species look very similar but can be distinguished by their scale patterns and fin ray counts. Some bullies are rare, threatened or endangered, while others are common and widespread.

Overview

Bullies all have two dorsal fins, a rounded tail, scales and a blunt head. They swim with a darting motion, staying close to or even touching the substrate. When at rest, they often appear to be 'standing' on their front fins. Some species are adept climbers and can scale waterfalls or the walls of tanks or aquariums. They mainly eat insects, though larger species may feed on fish eggs, snails, crustaceans, whitebait and other smaller native fish.

Like other native New Zealand freshwater fish, bullies are often found in smaller rivers, streams and lakes, where they mostly remain hidden. Bullies can be found throughout New Zealand, with many species' distributions overlapping. However, in general they are most commonly found in areas of lower elevation. This is especially true for the diadromous species (bluegill, giant, redfin and some common bullies), which mostly exhibit the migratory behaviour known as 'amphidromy'. In this process, the young spawn in fresh water but soon wash out to sea, where they develop before migrating inland to fresh water.

The breeding behaviour is similar between most species. Spawning takes place once annually, except for the bluegill bully and common bully, which are thought to spawn twice a year. The female lays up to several thousand eggs under wood, rocks or other hard material in fresh water. The male fertilises them and then guards the nest until they hatch. Neither parent cares for the young after they hatch. Among amphidromous species, juveniles stay at sea for three to four months and return to fresh water when they are about 15 to 20 millimetres long. Non-diadromous species (Cran's, Tarndale and upland) remain in fresh water for their entire lives. The juveniles of all species mature at one or two years.

While bullies share many features, the different species do have distinguishing characteristics. The bluegill bully (G. hubbsi) is the smallest, with a narrow arrow-shaped body. It can be distinguished from other bullies by its bright blue gill cover behind its head and dark spots on its cheeks. It lives in swiftly moving water in rivers and streams, feeding on mayfly larvae and small aquatic insects. It is found throughout New Zealand except for Fiordland, Steward Island and Chatham Island.

The common bully (G. cotidianus) looks like several other species of bullies. Often exceeding 120 millimetres in length, it is among the largest species. It is very common throughout New Zealand and found on both the North and South Island as well as Stewart Island and Great Barrier Island. Typically diadromous, populations in land-locked lakes have become non-diadromous.

The Cran's bully (G. basalis) looks much like common, upland and giant bullies. Male Cran's bullies have a distinctive bright pink-orange dorsal fin. Found in rivers and streams throughout North Island, Cran's bullies often live in the same habitats as common and upland bullies.

The giant bully (G. gobioides) is the largest, with examples recorded at over 250 millimetres, though it is more commonly seen in the same size range as the common bully, which it closely resembles. The two species can be distinguished reliably by their number of dorsal fin spines, with seven in the giant bully compared to six in the common bully. The giant bully lives in slow-moving water, such as tidal and estuarine areas near the coast throughout most of New Zealand. Its life cycle is poorly understood.

The redfin bully (G. huttoni) is the most distinct, as adult males have bright red marks on the fins, cheeks and body. Females have similar markings in brown. Redfins can grow to 120 millimetres. They live in moderate-flowing runs and pools of rocky streams throughout North and South Island, Stewart Island and the Chatham Islands, particularly in coastal areas.

The Tarndale bully (G. alpinus) is slender, bullet-shaped and olive brown. Found only in a remote area of Marlborough, it lives in the sub-alpine tarns of the Clarence and Wairau Rivers' headwaters.

The upland bully (G. breviceps) grows to about 80 millimetres long. Females and juveniles look similar to other bullies, and their territorial overlap with Cran's bullies means experts rely on microscopic examination for identification. However, the adult male has distinctive orange coloration on the dorsal fin, head and cheeks. Upland bullies live in the southern North Island, the East Coast of South Island, a few West Coast rivers on South Island and Stewart Island.

Bullies Today

Most bully species have widespread and stable populations. In 2013 the New Zealand Department of Conservation assessed the conservation status of all the freshwater fish in New Zealand. It determined that four of the seven species of bullies were not threatened under the New Zealand Threat Classification System. The bluegill and the redfin bullies were deemed at risk and declining, though with large existing populations of over one hundred thousand individuals. The Tarndale bully, meanwhile, was listed as at risk due to its naturally uncommon status. It is restricted to a small geographical area, and the population size is unknown.

In 2014 the International Union for Conservation of Nature and Natural Resources listed the bluegill bully as vulnerable and the redfin bully as near threatened. Both had declining populations. It listed the other five species as of least concern, with all but the common bully having stable populations. The population trend of the common bully was unknown.

Threats to bullies include loss and degradation of habitat due to changes in land use, forestry and agricultural development, and predation by introduced species. As of the late 2010s no conservation methods were being undertaken specifically for any bully species.

Bibliography

Balance, Alison. "Shy Fish, Bold Fish—Insights into the Lives of Native Fish." Radio New Zealand, 21 Apr. 2016, www.radionz.co.nz/national/programmes/ourchangingworld/audio/201797646/shy-fish,-bold-fish-insights-into-the-lives-of-native-fish. Accessed 8 Jan. 2018.

"Bluegill Bully." Rare Species, New Zealand Forest Owners Association, 2018, rarespecies.nzfoa.org.nz/species/bluegill-bully. Accessed 8 Jan. 2018.

"Bullies." New Zealand Department of Conservation, New Zealand Government, www.doc.govt.nz/nature/native-animals/freshwater-fish/bullies. Accessed 8 Jan. 2018.

"Bullies." NIWA Taihoro Nukurangi, 2016, www.niwa.co.nz/freshwater-and-estuaries/nzffd/NIWA-fish-atlas/fish-species/eleotridae. Accessed 8 Jan. 2018.

Field, Rick. "Native Fish." The Brook Waimarama Sanctuary, 7 Feb. 2012. www.brooksanctuary.org/news/native-fish. Accessed 8 Jan. 2018.

"Fish (New Zealand Freshwater)." Taranaki Educational Resource: Research. Analysis and Information Network, 2 Jan. 2017, www.terrain.net.nz/friends-of-te-henui-group/fish-freshwater-new-zealand.html. Accessed 8 Jan. 2018.

Parminter, Alice. "Rare Redfin Bully Fish Found in Auckland Stream." Stuff, 23 Mar. 2016. www.stuff.co.nz/auckland/78136675/rare-redfin-bully-fish-found-in-auckland-stream. Accessed 8 Jan. 2018.

"Redfin Bully." Rare Species, New Zealand Forest Owners Association, 2018, rarespecies.nzfoa.org.nz/species/redfin-bully. Accessed 8 Jan. 2018.

"Scientists Hunting for New Fish Species." The Country, nzherald.co.nz, 8 Nov. 2017. www.nzherald.co.nz/the-country/news/article.cfm?c‗id=16&objectid=11941798. Accessed 8 Jan. 2018.

"Tarndale Bully." Rare Species, New Zealand Forest Owners Association, 2018, rarespecies.nzfoa.org.nz/species/tarndale-bully. Accessed 8 Jan. 2018.