Elongate killifish

Where they come from

Titanolebias elongatus is one of those wild annual killifish that makes you realize nature has a sense of humor. They come from seasonal pools in South America (Paraguay/Argentina region), where the water exists for a short window, then dries out. The adults live fast, breed hard, and the eggs ride out the dry season in the mud.

Setting up their tank

This is an expert fish mostly because they do not forgive sloppy setups. Think species tank, simple layout, and water you can keep stable. I have had the best luck treating them like a project tank, not a community fish you toss into a planted display.

• Tank size: 10-20 gallons for a pair or trio works. Bigger is fine, but keep it easy to manage and cover tightly.
• Lid: non-negotiable. They can jump, especially at feeding time.
• Filtration: gentle sponge filter or air-driven box filter. You want clean water without blasting them around.
• Substrate: if you plan to breed, give them a deep container of peat/coir (or a "spawning box" filled with it). If you are not breeding, bare bottom is honestly easier.
• Decor: a few clumps of Java moss, floating plants, and some line-of-sight breaks (wood, leaf litter) so the female can get away.
• Light: moderate. Bright lights with no cover tends to make them edgy. Floating plants help.

Water-wise, aim for clean and consistent. Neutral to slightly acidic is usually fine, and moderate hardness is not a dealbreaker if you keep everything stable. Temperature in the low-to-mid 70s F is a good starting point. Warmer speeds them up and shortens their already short lives, so I do not cook them.

What to feed them

They are predators with a ridiculous feeding response. If it wiggles, it is food. In my tanks, live and frozen foods are the difference between "surviving" and actually putting on size and condition.

• Staples: frozen bloodworms, mysis, chopped krill, chopped prawn, good quality carnivore pellets (as backup, not the main diet).
• Best conditioning foods: live blackworms, live daphnia, mosquito larvae (where legal/safe), white worms in moderation.
• For youngsters: baby brine shrimp, microworms, chopped blackworms as soon as they can take it.

Watch their bellies. They will overeat if you let them, then sit around like a sausage. That sounds funny until you are dealing with bloaty, sluggish fish in a warm tank. Skip a day now and then and keep the diet varied.

How they behave and who they get along with

Elongatus is not a "cute little community killie." The male is bold, pushy, and built to eat smaller fish. Even the female is no pushover. They are also surprisingly reactive to movement outside the tank. Sudden shadows and they are in the lid.

• Best setup: species-only.
• Tankmates: I do not recommend them. Anything small becomes food, anything similar-sized becomes a stress trigger, and you are still stuck managing extra bioload.
• Intraspecific behavior: keep 1 male with 1-2 females if you have room and cover. Two males is asking for trouble unless the tank is large and structured, and even then it is a gamble.

Breeding tips

Breeding annuals is a whole hobby inside the hobby. The cool part is you can "bank" eggs and raise batches later. The annoying part is dialing in the dry time and not molding your whole clutch.

Condition them hard on live/frozen foods for a couple weeks. Give them a peat/coir tub 2-4 inches deep. They will dive into it and lay eggs below the surface. If they are spawning, you will see them disappear into the medium together.

• Collecting: pull the peat tub every 1-2 weeks (or sooner if you are worried about adults eating eggs).
• Processing: gently squeeze out excess water until the peat is just damp, not dripping.
• Incubation: store in a breathable bag/container at stable room temp. Label the date and species. Check occasionally for mold.
• Hatching: re-wet with cool, clean water in a shallow tray. Gentle aeration helps. Some batches hatch fast, others need a second dry period (do not panic if you do not get 100% on the first wet).
• Raising fry: start with baby brine shrimp ASAP. Keep water very clean and do frequent small water changes.

Do not be surprised if adults only live a handful of months once they are grown. That is normal annual killifish stuff. The eggs are your "next generation," so staying organized with dates and batches saves a lot of frustration.

Common problems to watch for

• Jumping: tight lid, cover gaps around airlines/cords, and do not spook them with sudden lights.
• Water quality slide: overfeeding plus heavy protein foods can crash things. Siphon leftovers and do regular water changes.
• Bloat/constipation: too many rich foods (especially worms) without variety. Try more daphnia, smaller meals, occasional fasting day.
• Beat-up females: male harassment in sparse tanks. Add cover, reduce line-of-sight, or separate the male.
• Egg loss to fungus: peat too wet, stale storage, or poor airflow. Keep it damp, not wet, and check batches regularly.
• Parasites from live foods: quarantine live foods when you can, and do not collect from questionable water.