Peten tetra

Where they come from

Peten tetras (Astyanax petenensis) come from Central America, especially the Yucatan and Peten region - think warm, limestone-influenced waters, lakes, slow rivers, and vegetated edges. They are not the delicate little blackwater tetra type. These are tougher, more food-motivated fish that act like they grew up competing at a buffet.

Setting up their tank

Give them space. They look like a simple silver fish in the store, then they put on size and attitude at home. A longer tank makes your life easier because they like to cruise, chase, and reorganize the social order all day.

• Tank size: I would not do less than a 40 breeder for a group. Bigger is noticeably calmer.
• Group size: 8-12 is where they start acting like a proper school instead of a few individuals squabbling.
• Filtration: moderate to strong. They are messy eaters and they appreciate some current to play in.
• Temp: mid-70s F is a comfortable middle ground (roughly 24-26 C).
• pH/hardness: they handle neutral to moderately hard water well. Stability beats chasing numbers.

Decor wise, think open swimming room with breaks in the line of sight. I like a sand or small gravel bottom, a few chunks of wood or rock, and plants that can handle a little abuse. They will pick at soft new growth if they are bored or underfed.

What to feed them

These fish are enthusiastic eaters. The trick is keeping them well-fed without turning the tank into a nitrate factory. I feed smaller amounts more often and let the filter and water changes do their job.

• Staple: a decent quality flake or small pellet (they will take bigger pellets as they grow).
• Protein rotation: frozen bloodworms, brine shrimp, mysis, chopped krill, or a good gel food.
• Greens/fiber: spirulina flakes, veggie-based pellets, blanched zucchini or spinach (they will nibble).
• Occasional treats: live foods if you have them (daphnia is great for keeping them busy).

How they behave and who they get along with

They are active, bold, and social. In a good-sized group they spend a lot of time schooling, sparring without damage, and rushing the front glass the second you walk by. In small numbers, they tend to single out a fish and turn into a fin-checking committee.

• Good tankmates: medium, sturdy fish that are not easily bullied (larger livebearers, many cichlids that are not tiny, robust barbs, larger rainbowfish).
• Use caution: slow fish with long fins (angelfish, fancy guppies, some gouramis).
• Not a match: tiny nano fish and small shrimp. Anything bite-sized will eventually get tested.

They do best with fish that can handle their pace. If your tank is calm and slow-moving, they will stick out like a pack of toddlers in a library.

Breeding tips

They are egg scatterers, and they are not sentimental parents. If they spawn in the main tank, the eggs usually become a snack pretty quickly. If you actually want fry, you will want a simple breeding setup.

• Set up a separate tank with a sponge filter and something for eggs to fall into (spawning mop, marbles, or a mesh/grate).
• Condition the adults with heavier frozen/live foods for a week or two.
• A small cooler-water change can trigger spawning in my experience, especially after conditioning.
• Pull the adults after you see spawning activity or eggs, or the eggs will not last long.

Fry are tiny at first, so plan for infusoria or a commercial fry starter food, then move to baby brine shrimp as soon as they can take it. The fry grow fast once they are on BBS.

Common problems to watch for

Most issues I have seen with Peten tetras come from keeping them too cramped, too few in number, or overfeeding because they act like they are starving 24/7. They are hardy fish, but they will absolutely bring out the weak points in your maintenance routine.

• Fin nipping: usually small group size, not enough space, or inconsistent feeding.
• Cloudy water and algae: classic result of heavy feeding plus not enough water changes/filtration.
• Ich after new fish: they handle treatment fine, but quarantine new arrivals if you can.
• Jumping and injuries: lid gaps, startled fish, or aggressive tankmates.
• Plant destruction: boredom or hunger. More cover and a bit more varied feeding helps.