Starhead topminnow

Where they come from

Starhead topminnows (Fundulus dispar) are a North American killifish that shows up in the Great Lakes region. Theyre a cool little surface fish from weedy margins, slow backwaters, and shallow shore zones where theres cover, insects, and changing conditions day to day.

That background matters because theyre not a typical community fish. They do best when you lean into that wild, plant-choked shoreline vibe instead of treating them like small tetras.

Setting up their tank

Think long and shallow if you can. They live at the surface and like room to cruise. A 20 long works nicely for a small group, and bigger is always easier with their personality and breeding behavior.

• Footprint over height. A 20 long beats a tall 20 for these.
• Lid is non-negotiable. They jump, especially during spats and spawning.
• Gentle flow. Sponge filters or a baffled HOB work well.
• Lots of surface cover: floating plants, overhanging stems, or even a strip of plastic craft mesh tucked under floaters.
• Dense plants around the edges (hornwort, guppy grass, vallisneria) plus a few open lanes to patrol.

Water wise, theyre not super fussy about numbers so much as stability and oxygen. I keep them in cool-to-mid temps (mid 60s to low 70s F) with good aeration. They handle harder water fine, and moderate hardness actually seems to make life easier (better plant growth, fewer weird stressy moments).

What to feed them

These are surface hunters. In my tanks they ignore a lot of sinking foods and go crazy for anything that wiggles or floats. If you want them to color up and spawn, live and frozen foods do the heavy lifting.

• Frozen: bloodworms, brine shrimp, daphnia, mysis (small pieces).
• Live: mosquito larvae (where legal), grindal worms, fruit flies, blackworms.
• Dry: floating micro pellets, small sticks, crushed flakes (use as backup, not the whole diet).

I feed small amounts 1-2 times a day. Theyll act like theyre starving even when theyre not, so watch bellies and dont let food rot under the plants.

How they behave and who they get along with

Starheads have that classic topminnow vibe: curious, alert, and a little bossy. Males posture at the surface and can be rough on each other in tight quarters. In a planted tank with a group, the chasing spreads out and the tank feels way calmer.

• Keep them in a group, not a pair. 6+ is a good starting point if the tank is sized for it.
• Aim for more females than males if you can. A 1 male to 2-3 females ratio keeps the heat down.
• They spend most of their time at the top, so pick tankmates that wont constantly compete for that space.

Tankmates are where they earn the advanced label. Theyre not mean like a cichlid, but theyll pick at slow fish near the surface and they will eat tiny tankmates. They also get stressed by hyperactive fin nippers.

Breeding tips

If you keep them happy, theyll usually try to spawn on their own. They scatter eggs in fine plants and floating roots. The trick is keeping the eggs and fry from getting vacuumed up by hungry adults (because yes, theyll snack on them).

• Give them a spawning mop (floating yarn mop) or a thick mat of guppy grass/hornwort at the surface.
• Condition with live/frozen foods for 1-2 weeks.
• Watch for males herding females into the plants and doing quick surface shimmies.

For actual fry production, I do one of two things: move the adults out after a few days of spawning, or pull the mop/plants and hatch the eggs separately. Eggs tend to do fine with gentle aeration and clean water. Once fry are free swimming, they need tiny food right away.

• First foods: vinegar eels, microworms, baby brine shrimp, powdered fry food as a helper (not the main course).
• Keep the fry tank shallow and clean. Siphon gunk daily with airline tubing.
• Add floating plants. Fry hang under them and pick at microorganisms.

Common problems to watch for

• Jumping: almost always from spooking, chasing, or open tops. Fix with a tight lid and more cover.
• Bullying: too many males, too small a tank, or not enough surface structure. Add floaters and rearrange plants, or separate a bully.
• Chronic skittishness: bright light and bare surface. Give them shade and a calm top zone.
• Wasting away: theyre often picky at first. Make sure theyre actually eating, and start with frozen/live.
• Fin damage: usually from tankmates or male sparring. More cover and a better ratio helps more than medication.

Disease-wise, theyre not uniquely fragile, but they dont love warm, stagnant water. If you run them hotter like tropical community fish, they seem to burn through oxygen and get stressed. I also quarantine anything new because external parasites show up fast on surface fish.