Melanorivulus ivinhemensis

Where they come from

Melanorivulus ivinhemensis is a small South American killifish from the Ivinhema River basin in Brazil. Think shallow, slow side creeks with leaf litter, grasses, and dappled shade. Water is usually soft, a bit tannin-stained, and there is almost no current.

Setting up their tank

A 10-gallon works for a pair or trio. For a small group, I like a 15- or 20-long. The lid needs to be tight. They are expert jumpers and will find even tiny gaps.

• Temperature: 72-76 F (22-24.5 C)
• pH: 5.8-7.0
• Hardness: 1-8 dGH, low KH
• Flow: very gentle - sponge filter level
• Lighting: dim to moderate with floating plants

Use a dark, fine substrate with leaf litter (catappa, oak) and a bunch of cover: fine-leaved plants, moss, or spawning mops. Floating plants calm them down and bring out better color. A small air-driven sponge filter is perfect.

Keep maintenance steady and boring: weekly 20-30% water changes with water that matches temperature and TDS. Sudden swings stress them out more than slightly imperfect numbers.

What to feed them

They are micropredators and really wake up for live foods. Most will learn to take quality small pellets or crushed flakes, but starting them on live or frozen makes life easier.

• Daily staples: live or frozen baby brine shrimp, daphnia, cyclops
• Treats: mosquito larvae (seasonal), grindal/white worms in moderation
• Dry foods: small soft pellets or fine flakes once they recognize them
• For fry: infusoria/green water, vinegar eels, microworms, then BBS

How they behave and who they get along with

Peaceful but a bit feisty with their own kind, especially males posturing at the surface. In a planted tank with broken sightlines, a single male with 2-3 females works well. Multiple males can work if the tank is long and packed with cover.

• Good with: tiny, calm fish like pencilfish, small rasboras, ember tetras, pygmy Corydoras
• Also fine with: small snails; adult shrimp are usually OK, babies may be snacks
• Avoid: fin nippers, fast boisterous fish, or anything that hogs the surface

Breeding tips

They are non-annual mop spawners. That means they lay small batches of eggs daily in fine plants or yarn mops, and the eggs hatch in water. You do not need to dry the eggs to get a hatch.

• Set up a pair or trio with 2-3 floating mops and gentle light.
• Condition with live foods for a week.
• Check mops daily and pick eggs with your fingers or a pipette.
• Incubate eggs in a small container with tank water, gentle aeration, and a leaf or two for tannins.
• At 74 F, eggs usually hatch in 10-14 days. Move fry to a separate rearing box if you want better survival.

Fry are tiny and hang near the surface. Start with infusoria or vinegar eels for a few days, then switch to baby brine shrimp. Keep the surface calm and covered with a bit of floating plant so they feel safe.

Common problems to watch for

• Jumping: number one cause of losses. Tight lid, every gap sealed.
• Overheating: they handle warm spells, but long-term high 70s to 80s F shortens lifespan. Aim low to mid 70s.
• Strong flow: they hug calm water. Baffle or switch to a sponge filter.
• Refusing dry food: use a live/frozen-to-dry transition. Do not rely on flakes alone.
• Shyness and pale color: add floating plants, reduce light, and boost cover.
• Velvet or ich after shipping: quarantine new fish, gentle salt or medication as needed.
• Egg fungus or poor hatch: collect eggs more often, add tannins, and keep incubation water clean and gently aerated.

Keep the setup quiet, the lid tight, and the food varied, and Melanorivulus ivinhemensis will reward you with relaxed behavior and steady spawning. They are a joy once you dial in the soft water and mellow flow.