Banded Killifish (Fundulus Diaphanus): Ultimate Care Guide

Banded Killifish is a temperate freshwater species native to North America. Its range includes the east coast, Great Lakes region and down to Minnesota. Named for the vertical banding patterns along its sides, coloration on males is more distinct along with other differences. Similar to the brackish water dwelling Mummichog, the Banded Killifish is the only freshwater killifish in North America.

Seldom seen in aquariums due to its high maintenance requirements, Banded Killifish can be a challenging fish to properly care for.

A shoaling fish, Fundulus Diaphanus appreciates being part of a school of three to six. Often found in shallow ponds, rivers and lakes with sandy gravel or mud bottoms. A natural habit for these fish will also include driftwood and lots of vegetation.

Certain U.S. states have classified the Banded Killifish as threatened or endangered. This is only a regional classification as populations are large in some parts of the U.S.

When kept in a native fish tank with other North American specimens, the Banded Killifish can be eye-catching and a good conversation starter. Up to the challenge of keeping this unusual native fish? Read on for more information to help increase your chances of success.

Banded Killifish Care

Banded Killifish are carnivorous and native to temperate waters so ensure proper water temperature and select appropriate tank mates. Include up to 6 individuals as this is a shoaling species. They often swim in the upper regions of a tank, so ensure your plants and other Aquascaping reaches high enough to provide cover and hiding spaces.

Males of the species will fight each other so plan for only one to two males in a group of six. Note that because they are carnivores they are more than willing to eat smaller fish. This species is mostly good-natured though high-strung. They are likely to annoy tank mates rather than attack. Safe tank mate selection would include larger fish and species that are fast and active.

Banded Killifish (Fundulus Diaphanus)
Banded Killifish (Fundulus Diaphanus). Smithsonian Environmental Research Center, CC BY 2.0

Banded Killifish Temperature

Banded Killifish are a temperate species so ensure their water temperature doesn’t rise above 70° F (21° C) except during breeding. Depending on external environment, a refrigerated chiller may be required to keep water temperature within the ideal range.

Banded Killifish Water pH

Banded Killifish prefer water with a pH between 7.0 and 8.0. They also prefer hard water of 10-20 dH.

Banded Killifish Size

Banded Killifish usually mature to approximately 3 to 4 inches in length. Specimens as large as 5.5 inches have been found in the wild; though they are unlikely to grow to that size in most aquariums.

Banded Killifish Food & Diet

Banded Killifish are carnivores so plan to feed with a mix of live and frozen food. If you decide to try feeding carnivore pellets, make sure you use the floating type. These top-dwelling fish may not go after sinking pellets.

Eager eaters, your Banded Killifish should devour most foods intended for carnivorous fish. You may find that they require enough live food to justify investing in live food culture supplies.

Banded Killifish Lifespan

A short-lived species, Banded Killifish only live for just over 2 years. A lifespan of 3 years is the maximum and unusual.

Banded Killifish Tank Size

Banded Killifish are energetic swimmers. Combine that with the need to maintain a school of 6 or more individuals and you should start with a minimum tank size of 30 gallons or preferably, 55 gallons. Since this species swim in upper tank areas you have room in the mid to lower regions for appropriate tank mates.

Banded Killifish Tank Setup

When preparing a tank for Banded Killifish ensure that it is covered and has lots of plant material to give them hiding spaces. Secure tank covering is critical as this species will jump. If planning a community nature aquarium your Aquascaping should include sufficient plant material. Driftwood, rocks and other hardscaping material should be utilized. This species likely won’t make use of lower tank areas, but other species in a community tank will..

Mimicking this species’s natural environment of slow moving streams and lakes would require a silty soil, or even mud bottom. In a display aquarium, using these types of substrates is less than ideal. In most cases a planted aquarium substrate works. Banded Killifish will feel most at home in a planted tank so you’ll likely want a substrate that will support moderate to heavily plant load.

You will want filtration, but not too much. Banded Killifish prefer slow moving waters. A powerful filter may generate too much water current for this fish’s comfort. It’s best to use a filter that turns over four times the volume of your tank in an hour. For instance, a 55 gallon tank would need a filter that runs a bit over 200 GPH (gallons per hour).

Because these fish are native to temperate environments you may have issues keeping your tank water cool enough. To keep the water from exceeding 70° F (21° C) you might need to invest in a chiller. The most popular of these require some plumbing to integrate into your tank. Talk to your aquarium supplier to find out how large of a chiller you’ll need based on your tank size and setup.

Banded Killifish Breeding

Banded Killifish breed in the summer months so water temperature will need to be increased to 72° – 75° F to stimulate breeding. A good procedure is to move a male and two females to a smaller breeding tank outfitted with breeding mops. Breeding mops, which can be purchased or homemade, use synthetic yarn to simulate clusters of plant foliage. Aside from breeding mops, you will want to outfit this tank with a sponge filter and possibly a heater.

Expect a female to lay around 50 eggs. Check your breeding mops daily for signs of eggs. These should hatch in 10 to 12 days. Banded Killifish may eat eggs and they will definitely eat any fry that hatch. Move adults out of the breeding tank as soon as possible after eggs have been laid.

Observe the eggs for signs of hatching. As soon as you see fry, begin feeding with brine shrimp. When fry have reached ½ an inch in length and are taking adult foods they can be moved from the breeding tank.

Banded Killifish Disease

Banded Killifish are susceptible to the same diseases as other freshwater fish. Due to their high maintenance requirements this species may be more susceptible to diseases when kept in an aquarium. Be on the lookout for Mouth Fungus and Fish Fungus which exhibit as a white wool-like structure on different body parts.

The root causes of many diseases in Banded Killifish can be traced to poor water quality, poor food quality or incorrect tank temperature. To keep your fish healthy you’ll need to monitor their environment and make adjustments when needed.

Banded Killifish Tank Mates

Though not an aggressive species, Banded Killifish are very active. They may harass some tank mates that aren’t sufficiently large or fast swimmers. These fish mainly swim in upper tank regions and seldom bother species that stay in lower areas.

Good tank mate choices could be Rainbow and Greenside Darters, Banded Sunfish. Also Northern Hogsuckers, as they are bottom feeders, can fill in the lower areas of the tank.

Banded Killifish are mostly trouble-free as tank makes. You should avoid pairing them with large carnivorous fish who might decide they are food.

Where can I find Banded Killifish for sale?

Finding Banded Killifish for sale is a challenge. Specialist sources exist, but often these fish need to be caught in the wild. Check your local laws before obtaining fish from natural sources. Be aware that this species is specially protected in certain areas of the U.S.

Western Banded Killifish vs Eastern Banded Killifish

Western Banded Killifish and Eastern Banded Killifish are the two main wild varieties of this species in North America. Differences between the two are subtle, often needing more than one specimen for confirmation. One method of determination is lateral row scale count. Western Banded Killifish will have scale counts between 36 and 44. Eastern Banded Killifish have scale counts between 48 and 51.

An added complication here is interbreeding between Eastern and Western varieties. This has become more of a factor than when the first classifications of these varieties were made in the 1800s. Genetic analysis may be required to make a positive determination.

Banded Killifish vs Mummichog

Banded Killifish and Mummichong are both types of killifish though Mummichongs are larger–the female can grow to 6 inches. Banded Killifish have dark bars on a light side. Mummichong have light bars on a dark side and bright spots. Mummichong have a greater tolerance for salinity and can be found in brackish coastal waters such as salt marshes and estuaries. They are also an extremely hardy species, capable of living in a wide range of aquatic environments.

Mimmichongs and Banded Killifish are capable of interbreeding. Be aware of this fact if you plan on keeping them together as tank mates.