Bibosi rivulus

Where they come from

Bibosi rivulus (Anablepsoides bibosi) is a little South American killifish from shaded forest creeks and swampy edges in the upper Amazon basin of Bolivia. Think leaf litter, tannin-stained water, and very gentle flow. They spend a lot of time near the surface, picking at tiny bugs that fall from overhanging plants.

Tank setup

They are small, but give them room to cruise the surface. A 10-15 gallon with a lid works for a pair or trio. They appreciate dim light, floating plants, and calm water. Footprint matters more than height.

• Lid: tight-fitting with no gaps. They are expert jumpers.
• Filtration: air-driven sponge or a very gentle HOB with a baffle. They dislike strong current.
• Decor: floating plants (Salvinia, frogbit), fine-leaved plants or yarn mops, leaf litter, and wood. Dark substrate helps them color up.
• Water: soft to moderately hard, slightly acidic to neutral (pH ~5.8-7.2). I keep mine around 72-76 F (22-24 C).
• Lighting: on the dim side. Let the floaters cover a third to half of the surface.

What to feed them

They are micro-predators with an upturned mouth, so think small foods at the surface. Live and frozen get the best response. Mine wake up for baby brine, daphnia, and mosquito larvae. Some will take quality micro-pellets once they trust the tank.

• Staples: live or frozen baby brine shrimp, daphnia, cyclops, grindal/white worms.
• Treats: mosquito larvae, fruit flies (wingless), small bloodworms.
• Dry foods: tiny floating pellets or flakes crushed very fine. Mix with live foods to train.

Behavior and tankmates

Peaceful but a bit territorial at the surface. Males spar and display, so give them cover and line-of-sight breaks. They are much more confident in a quiet, planted setup.

• Best kept as a pair or 1 male with 2 females in a species tank.
• If you want tankmates: small, calm fish that do not crowd the surface, like pencilfish or tiny tetras. Keep the group light so food reaches the rivulus.
• Avoid: fast surface fish (hatchetfish can outcompete), fin nippers, big shrimp (they will harass tiny shrimplets) and anything boisterous.

Breeding tips

They are non-annual killifish that lay adhesive eggs in fine plants or mops. You can breed them in the display if it is jungle-thick, but collecting eggs from a spawning mop is much easier.

• Set a spawning mop near the surface or use a clump of fine-leaved plants.
• Keep a pair or 1M:2F. Condition with live foods for a week.
• Check mops every few days. Eggs are small, clear to amber, and stick to the fibers.
• Incubate eggs in a small container with tank water, a drop of methylene blue, and gentle airflow. At 24 C they typically hatch in 10-14 days.
• Move hatched fry to a rearing box with infusoria, then feed vinegar eels, microworms, and newly hatched brine shrimp.
• If raising fry with parents, pack the tank with plants and floaters. Some fry will make it, but adults will snack on them.

Common problems to watch for

• Jumping: the number one cause of losses. Double-check the lid after every maintenance session.
• Surface stress: bright lights and strong current make them skittish. Add floaters and baffle the filter.
• Reluctance to eat dry food: start with live/frozen, then mix in tiny pellets slowly.
• Fungused eggs: improve egg airflow and cleanliness, or pick off white eggs. A little methylene blue helps.
• Internal parasites in new imports: watch for wasting and white stringy poop. Quarantine and treat appropriately if needed.
• Heat fatigue: consistently high temps shorten lifespan and hurt appetite. Keep them in the low-to-mid 70s F if you can.