Barrens topminnow
Fundulus julisia
Barrens topminnow features a slender body with a pale grey-green coloration and distinct dark spots along its sides, typical of its species.
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About the Barrens topminnow
Fundulus julisia is a rare Tennessee Barrens Plateau topminnow that lives near the surface in springs and spring-fed creeks, often around aquatic vegetation, feeding largely on small aquatic insects. It is federally listed as Endangered (U.S., 2019) and is the focus of captive propagation and reintroduction efforts.
Also known as
Quick Facts
Size
7.0 cm TL
Temperament
Peaceful
Difficulty
Advanced
Min Tank Size
20 gallons
Lifespan
3-5 years
Origin
North America (central Tennessee, USA)
Diet
Carnivore/insectivore - small live/frozen foods (insects, crustaceans) plus will usually take quality dry foods
Water Parameters
10-26°C
7-8
5-15 dGH
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Calculate heater sizeCare Notes
- Give them a long tank with lots of surface area (20 long or bigger) and a tight lid - they jump when spooked, and they spook easily.
- They are native to springs and spring-fed creeks; match stable, clean, well-oxygenated freshwater conditions and avoid rapid swings in water chemistry.
- Keep the flow moderate and the surface well-oxygenated; a sponge filter plus a small powerhead aimed along the back wall works great without blasting them around.
- Feed like a picky micro-predator: live/frozen stuff (baby brine, daphnia, cyclops, mosquito larvae) gets the best weight and color; pellets work only if you train them and keep portions tiny.
- Tankmates need to be calm and not nippy - avoid fin-nippers and boisterous fish; small darters, non-aggressive minnows, and peaceful inverts usually work if they are not competing hard at the surface.
- They are plant/spawn-mop scatterers and will drop eggs over days; toss in a yarn mop or fine-leaf plants, pull the mop every few days, and hatch eggs in a small container with gentle aeration.
- Watch for surface bullying and stress: one pushy male can keep others pinned in corners, so keep them in a group with extra females and lots of sight breaks near the top (floating plants help).
Compatibility
Good Tankmates
- Small, chill livebearers like endlers or guppies (as long as nobody is a fin-nipper). They hang in the same upper water, but the topminnows are pretty polite and just want room to cruise.
- Peaceful, non-nippy small fishes that tolerate cooler, spring-like conditions (choose tankmates conservatively).
- Small, peaceful shiners/daces (think rosy red fathead minnows or similar non-aggressive native-style minnows). They keep to themselves and do not hassle the topminnows.
- Corydoras catfish - classic bottom crew. They stay out of the topminnows' way, and the topminnows do not bother them.
- Small, calm loaches like kuhli loaches - they are mostly nocturnal and bottom-oriented, so there is basically zero drama with topminnows.
- Peaceful small sunfish relatives are a no, but peaceful dwarf bottom fish like otocinclus are a yes - otos just graze all day and do not compete for the surface.
Avoid
- Anything nippy like tiger barbs or serpae tetras - they will harass surface fish and turn a peaceful topminnow into a stressed, hiding fish.
- Bettas or other territorial surface fish. Even if the betta seems chill, they often take offense to another fish living at the surface and it turns into constant posturing or chasing.
- Big mouth predators like larger cichlids (or any fish that can fit them in its mouth). Topminnows are slim, surface-oriented snacks in the wrong tank.
Where they come from
Barrens topminnows (Fundulus julisia) are one of those fish that make you stop and read the label twice. They are from a tiny area in Tennessee, living in clear, spring-fed streams over gravel and rock. Think cool-to-mild water, clean flow, and lots of little hiding spots along the edges.
You will often see them discussed in a conservation context. That is a big reason many hobbyists treat them more like a project fish than a casual community fish.
Setting up their tank
These are advanced mostly because they do not forgive sloppy water. They are tough in the sense that they are native fish, but they really want clean, oxygen-rich water and stable conditions. If your tanks sometimes run a little "seasoned" (read: nitrate creep, mulm, lazy water changes), pick a different fish.
A simple setup works best: a longer tank, good flow, and lots of cover along the edges. They use the surface a ton, but they also like to duck into plants when they feel watched.
- Tank size: 20 long is a nice starting point for a small group. Bigger is easier to keep stable.
- Filtration: sponge filter plus a small powerhead, or a hang-on-back with a prefilter sponge. You want movement without blasting them around.
- Lid: mandatory. Fundulus can jump, and they do it at the worst possible time.
- Substrate: sand or fine gravel with some smooth stones. Leaf litter is fine if you keep up with maintenance.
- Plants: floaters (salvinia, frogbit), and edge cover like java moss, guppy grass, or crypts. They like "lanes" to patrol near the surface.
If you can, run them a bit cooler than your usual tropical community tank. They do fine at typical room temps, and they tend to look and act better long-term without constant 78-80F heat.
Do not skip quarantine. Wild-type topminnows can come with external parasites and flukes, and you do not want to be guessing at treatments in a display tank.
What to feed them
They are surface hunters. If it lands on top and wiggles, they are interested. If it sinks fast, it might as well not exist. You can train them onto prepared foods, but you will get your best color and breeding behavior when you mix in live and frozen.
- Daily staples: small floating pellets, crushed flakes, or micropellets they can grab at the surface
- Frozen: bloodworms, daphnia, cyclops, brine shrimp (thawed and offered in small pinches)
- Live (my favorites for conditioning): blackworms, white worms (sparingly), daphnia, mosquito larvae where legal/safe
Feed small amounts more often instead of one big dump. They get competitive at the surface, and spreading food out reduces fin nips and keeps the shy ones eating.
If you are trying to get them breeding, bump up the live foods for a couple weeks and keep water changes steady. They respond fast to "springtime" signals: fresh water, good food, and stable temps.
How they behave and who they get along with
They are alert, busy fish. Males posture and chase, but it is usually more attitude than damage if you keep them in a group with lots of line-of-sight breaks. A single male in a bare tank will act like a little tyrant. A group in a planted tank acts way more natural.
- Best group: 1 male to 2-3 females, or a small colony with extra females
- Temperament: semi-peaceful, can be pushy at feeding time and around spawning spots
- Tankmates: stick to calm, similarly sized fish that do not need hot water
I would not mix them with slow, surface-hugging fish (like fancy guppies with big tails) because topminnows will outcompete them and may nip. Also skip big, bold fish that patrol the top and make them nervous. If they feel pressured, they spend more time hiding and you will see more jumping.
Anything that fits in their mouth is food. Tiny fry and very small nano fish can disappear, especially at night or right after lights-on.
Breeding tips
They will breed in the aquarium if you give them a place to put eggs and you do not keep the tank too "sterile." The easiest method is to provide spawning mops or dense moss and then either pull eggs/fry, or pull the adults after you see steady spawning.
- Spawning media: floating yarn mops, java moss mats, or fine-leaved plants near the surface
- Conditioning: heavy feeding of live/frozen for 2-3 weeks, then a couple larger water changes
- Egg collection: check mops every day or two and move eggs to a small container with gentle aeration
Eggs are usually pretty tough, but fungus can pick them off if you let dead ones sit. I like to remove any white eggs and keep a slow bubble nearby. Once fry are free-swimming, they want tiny foods right away.
- First foods: infusoria, rotifers, vinegar eels, then baby brine shrimp as soon as they can take it
- Grow-out: lots of small feedings and frequent water changes
- Cover: floaters and fine plants help fry feel safe and keep them up near food
If adults keep wiping out the fry, do not fight it. Just treat them like egg scatterers: use mops, pull eggs, raise fry separately. You will save yourself a lot of frustration.
Common problems to watch for
Most issues I see with Barrens topminnows come down to water quality, stress, or the tank being too warm and stagnant. They are surface fish, so they show oxygen problems early: hanging at the surface is normal, but rapid gulping and clamped fins is not.
- Jumping: almost always from spooking, chasing, or sudden changes (lights, big water change temp mismatch). Use a tight lid and keep the tank calm.
- Skin and gill parasites: flashing, staying pinned near flow, heavy breathing. Quarantine and treat deliberately, not randomly.
- Fin nipping: usually crowding, too many males, or feeding competition. Add cover, spread food out, fix the ratio.
- Wasting away: often internal parasites or not getting enough food at the surface. Watch individuals during feeding and adjust.
- Egg fungus: dead eggs left in the clutch. Remove white eggs and add gentle aeration.
Avoid treating blindly with a cocktail of meds. With uncommon natives like this, slow down: observe, confirm symptoms, and choose one treatment at a time. A lot of losses happen from "medicine panic" more than from the original problem.
If you keep up with clean water, give them flow and cover, and feed like you mean it, they are seriously rewarding fish. They have that wild, watchful personality that makes you want to pull up a chair and just stare at the tank for a while.
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