Northern studfish
Fundulus catenatus
The Northern studfish features a streamlined body with striking greenish-blue scales and distinct vertical black stripes along its flanks.
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About the Northern studfish
A big North American killifish, males glow turquoise-blue with orange-edged tails and fine red lines in breeding dress. It rockets along the surface in clear, cool creeks and can be feisty and jumpy, so a tight lid and roomy quarters are a must.
Also known as
Quick Facts
Size
20 cm (about 8 inches)
Temperament
Aggressive
Difficulty
Advanced
Min Tank Size
30 gallons
Lifespan
about 5 years
Origin
North America
Diet
Carnivore - aquatic insect larvae and small snails; accepts frozen foods and quality pellets
Water Parameters
15-25°C
6.5-7.5
5-12 dGH
Need a heater for this species?
This species needs 15-25°C in a 30 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Give them space: 30 gallons minimum, and bigger is better for adults that reach about 8 inches.
- Use a tight-fitting lid with every gap covered; this species is fast, surface-oriented, and very jumpy.
- Aim for cool, clean water with some flow, mirroring clear creeks; keep 15-25 C, pH 6.5-7.5, and 5-12 dGH.
- Run good filtration and keep the water well oxygenated; they handle clear, cool water best and can stress in heat spikes.
- Feed a meaty carnivore diet: aquatic insect larvae and small snails, plus frozen foods and quality pellets offered at the surface.
- Expect aggression and chasing; choose only robust, similarly sized tankmates and skip small or slow fish, or run a species-only setup.
- Aquascape for open surface runs and strong swimming, with some rock or wood to break line-of-sight so subdominant fish can get out of view.
Compatibility
Good Tankmates
- Robust, fast North American shiners/dace around 10-15 cm (e.g., larger Luxilus/Notropis) in a cool, high-flow tank - big enough not to be prey and quick enough to dodge surface sparring
- Larger darters (Etheostoma/Percina) that stay on the bottom with rock cover and strong current - little surface competition and similar cool, clear-water needs
- Madtoms/stonecats (Noturus spp.) of appropriate size - armored, nocturnal bottom catfish that ignore the surface and handle firm flow
- Rubberlip/Chaetostoma plecos - cool, high-oxygen bottom grazers the studfish typically ignores; avoid warm-water pleco species
- Weather loach (Misgurnus anguillicaudatus) in bigger-than-minimum setups - peaceful, cool-water bottom fish; choose adults too large to be chased or swallowed
Avoid
- Small fish or invertebrates that fit in its mouth (white clouds, small tetras, livebearer fry, shrimp, small snails) - will be hunted
- Slow or long-finned fish (bettas, fancy goldfish, veil angelfish) - likely to be harassed/nipped and outcompeted at the surface; many also prefer warmer water
- Other surface topminnows/killifish and multiple adult male studfish - intense surface rivalry and fighting
- Crayfish and large, territorial sunfish (Lepomis spp.) - claws or heavy aggression can injure or maim studfish
Northern studfish (Fundulus catenatus) is a large North American killifish built for speed. Males glow turquoise-blue with orange-edged tails and fine red lines in breeding dress. It is a powerful, surface-oriented fish that bolts in clear, cool creeks and can be both feisty and jumpy. This is an advanced species that needs space, tight covers, and careful stocking.
Origin and natural habitat
Native to North America, Northern studfish inhabit clear, cool creeks and small rivers. They spend much of their time near the surface, using quick bursts of speed in open water. High oxygen and clean, well-oxygenated flow characterize the places they do best.
Aquarium setup and water conditions
Think long, covered, and well-oxygenated. They are active surface cruisers that appreciate room to sprint and clean, moving water.
- Minimum tank size: 30 US gallons (larger is better for adults and activity level)
- Temperature: 15-25 C
- pH: 6.5-7.5
- Hardness: 5-12 dGH
- Water: freshwater, clear and well-filtered with noticeable current
Use a tight-fitting lid with sealed gaps; this species is a strong jumper. A long tank with open swimming lanes and good surface agitation is ideal. Provide line-of-sight breaks (rockwork, wood, hardy plants) to diffuse aggression. Substrates that suit creek setups, like sand or rounded gravel, work well.
Leave no escape routes. Northern studfish are powerful jumpers that will find the smallest opening.
Diet and feeding
Carnivorous. In nature they take aquatic insect larvae and small snails. In aquaria they accept frozen foods and quality pellets.
- Staples: frozen bloodworms, blackworms, mosquito larvae, and similar insect-based items
- Pellets: high-quality carnivore pellets; introduce alongside frozen foods if they are new to prepared diets
- Feeding style: offer small portions 1-2 times daily; they feed eagerly near the surface
If a new fish hesitates on pellets, pair them with frozen insect larvae at first, then gradually increase the pellet share.
Behaviour and tankmates
Listed as aggressive and known to be feisty, especially in confined quarters. They are fast, surface-focused fish that patrol open water and can hassle slower tankmates.
- Best kept in a roomy species tank or with other robust, fast, cool-water fishes that can handle assertive behavior
- Avoid slow, long-finned, or very small tankmates
- Provide multiple cover spots and broken sight lines to reduce chasing
Activity level is high. Extra space often lowers tension and helps channel their energy into cruising rather than constant sparring.
Common problems and how to avoid them
- Jumping losses: use a tight lid and cover all gaps around equipment
- Overheating or low oxygen: keep within 15-25 C and maintain strong filtration and surface agitation
- Bullying and fin damage: provide more space, add sight breaks, and avoid incompatible tankmates
- Water quality dips: this species comes from clean, clear water; keep up with filtration and frequent maintenance
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