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The Common bully (Gobiomorphus cotidianus) is a small, benthic, freshwater fish endemic to New Zealand. It is characterized by its robust, elongated body, typically mottled brown to olive-green coloration, and two distinct dorsal fins. It is a member of the Eleotridae family, commonly known as sleeper gobies, although it is often colloquially referred to as a 'bully' due to its somewhat aggressive territorial behavior, particularly during breeding.
Physical Characteristics
- Body shape
- elongated
- Coloration
- Highly variable, typically mottled brown, olive-green, or grey, often with darker blotches or bands. Coloration can change rapidly to match the substrate. Underside is usually paler.
- Scale type
- ctenoid
- Mouth position
- superior
- Distinctive features
- Two distinct dorsal fins (the first spiny, the second soft-rayed)., Large, upward-pointing mouth., Robust, somewhat flattened head., Pectoral fins are large and fan-like., Pelvic fins are separate (not fused into a disc like true gobies)., Lateral line is absent or inconspicuous.
- Dorsal fin
- Two dorsal fins; D1: VI-VIII spines, D2: 1 spine, 9-12 soft rays
- Tail fin
- Rounded to slightly emarginate caudal fin
- Pectoral fin
- Large, fan-like, 15-18 rays
- Distinctive fins
- Pelvic fins separate, I spine, 5 soft rays
Identification Tips
Two separate dorsal fins
Distinguishes it from true gobies which have fused pelvic fins and often a single dorsal fin.
Mottled coloration
Helps it blend into its varied freshwater habitats.
Separate pelvic fins
A key characteristic differentiating it from true gobies (Gobiidae).
Habitat
- Water type
- freshwater
- Depth
- Typically found in shallow waters, but can inhabit depths up to a few meters.
- Environment
- Lakes, slow-flowing rivers, streams, ponds, and estuaries. Prefers areas with good cover such as rocks, logs, aquatic vegetation, and undercut banks. Can tolerate a wide range of water conditions, including some brackish water.
- Geographic range
- Endemic to New Zealand, found throughout the North and South Islands, as well as Stewart Island and some smaller offshore islands. It is the most widespread and common bully species in New Zealand.
Aquarium Information
- Care level: intermediate
- Temperament: semi-aggressive
- Diet: carnivore
- Minimum tank size: 75 liters (20 gallons)
- Temperature: 10-22°C (50-72°F)
- pH level: 6.5-7.5
- Hardness: soft to moderately hard
- Compatibility: Best kept with other robust, similarly sized native New Zealand fish or in a species-specific tank. Can be territorial, especially males during breeding.
- Special requirements: Requires a well-oxygenated tank with plenty of hiding places (rocks, driftwood, plants) and a substrate of sand or fine gravel. Good filtration is essential. Can be sensitive to poor water quality.
Wild Information
- Conservation status: least concern
- Seasonality: Breeds primarily in spring and summer, but can be found year-round in suitable habitats. Activity may decrease in colder months.
- Market price: Not commercially fished for human consumption. Occasionally collected for the aquarium trade or scientific research.
- Commercial importance: low
- Taste: Not typically consumed.
- Texture: Not typically consumed.
- Nutritional value: Not typically consumed.
Key Facts
Sizebehavior
Typically 8-12 cm, maximum 15 cm.
Dietbehavior
Opportunistic carnivore, feeding on aquatic invertebrates (insect larvae, crustaceans), small fish, and fish eggs.
Reproductionbehavior
Males establish territories and guard nests of eggs laid by females on the underside of rocks or logs. Eggs hatch in 10-20 days, and larvae are pelagic for a period before settling to the bottom.
Lifespanbehavior
Typically 2-4 years in the wild.
Ecological Rolebehavior
Important prey item for larger fish (e.g., trout, eels) and birds. Also plays a role in controlling invertebrate populations.
Taxonomic Notesbehavior
Previously considered a subspecies of Gobiomorphus basalis (Upland bully), but now recognized as a distinct species, Gobiomorphus cotidianus, due to genetic and morphological differences. The name 'Upland bully' is sometimes still used interchangeably, but 'Common bully' is more appropriate for G. cotidianus.
Safety Information
Safe- Safety level: safe
- Venomous: No
- Edibility: not recommended
- Handling notes: No specific handling precautions are required beyond standard fish handling practices to minimize stress to the fish. They are not venomous and do not possess sharp spines that pose a significant threat.
Similar Species
Redfin bully (Gobiomorphus huttoni)
Gobiomorphus huttoni
Redfin bullies typically have distinct red or orange coloration on their fins, especially the pectoral and caudal fins, and often have a more streamlined body. They also have a more pronounced dark spot at the base of the pectoral fin. Common bullies lack this prominent red/orange fin coloration.
Giant bully (Gobiomorphus gobioides)
Gobiomorphus gobioides
Giant bullies are significantly larger, reaching up to 25 cm, and have a more robust, deeper body. They also tend to have a more pronounced 'hump' behind the head. Common bullies are much smaller, rarely exceeding 15 cm.
Bluegill bully (Gobiomorphus hubbsi)
Gobiomorphus hubbsi
Bluegill bullies are generally smaller and have a more slender body. Males often display iridescent blue or green patches on their opercula (gill covers) during breeding, which is absent in Common bullies.
Scientific Classification
- Kingdom
- Animalia
- Phylum
- Chordata
- Class
- Actinopterygii
- Order
- Gobiiformes
- Family
- Eleotridae
- Genus
- Gobiomorphus
- Species
- Gobiomorphus cotidianus
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