Long-finned glass tetra

Where they come from

Long-finned glass tetras (Xenagoniates bondi) come from South America, where they live in softer, slightly acidic waters with lots of plants, roots, and tannin-stained cover. They are one of those fish that look delicate because they are see-through, but they are not "fragile" if you give them stable water and calm tankmates.

Setting up their tank

Give them space to swim and a setup that breaks up sight lines. I like a longer tank over a taller one, because they use the middle of the water column and appreciate a runway.

• Tank size: I'd start at 20 gallons long for a small group, and 30+ gallons feels way easier to keep stable.
• Group size: 8-12 is where their behavior looks the most natural. Fewer than that and they get jumpy.
• Filtration: moderate flow is fine, but don't blast them. They do better with steady circulation than turbulence.
• Lighting: moderate. Too bright with no shade makes them skittish. Floating plants help a lot.
• Scape: plants (especially tall stems), driftwood, and a darker substrate make them show their fins more.

Water-wise, they are happiest in the usual "softish community" range. Think mid-70s F, neutral-ish or a bit acidic, and not hard like liquid rock. More than any exact number, they react to swings, so keep things consistent and do regular water changes.

What to feed them

Mine acted like classic micro-predators: they take small foods eagerly, especially anything that drifts and looks alive. If you only feed big flakes and walk away, the shy ones miss out.

• Staples: good-quality micro pellets and crushed flake that stays suspended for a bit.
• Frozen: daphnia, cyclops, baby brine shrimp, and finely chopped bloodworms as a treat.
• Live (if you do it): baby brine shrimp is basically a cheat code for color and conditioning.
• Plant matter: not a big focus, but they will pick at biofilm and tiny bits in the tank.

How they behave and who they get along with

They are schooling fish, but not in a tight "one blob" way all day. Expect loose cruising, then sudden synchronized turns when something spooks them. Once settled, they are peaceful and pretty confident in a planted tank.

Fin-nipping usually is not their thing, but long fins on them can attract the wrong kind of attention. Choose tankmates that are calm and not bitey.

• Good tankmates: other peaceful tetras, rasboras, hatchetfish (with a lid), pencilfish, Corydoras, small Loricariids, and most gentle dwarf cichlids.
• Use caution: barbs, serpae-type tetras, or anything known for nipping.
• Avoid: larger aggressive cichlids and chunky predators that see "transparent" as "snack."

Breeding tips

Breeding is possible but not the easiest "accidental spawn" tetra. The adults will happily eat eggs and tiny fry, and they like softer water for decent hatch rates.

• Set up a separate breeding tank (10-20 gallons) with a sponge filter and gentle aeration.
• Use a spawning mop or dense fine-leaf plants (java moss works) so eggs fall out of reach.
• Condition the group for a week or two on frozen/live foods.
• Move a pair or small group in the evening, then check for eggs the next morning.
• Pull the adults after spawning. If you leave them in, expect the eggs to vanish.

Fry are tiny. Start with infusoria or commercial fry food/powder, then move to newly hatched baby brine shrimp once they can take it. Clean water matters a lot here, so do small, frequent water changes rather than big ones.

Common problems to watch for

Most issues I have seen come from stress and instability rather than a mysterious disease. Their transparent bodies make them look "off" faster than opaque fish, so you notice every little thing.

• Spooking and glass-surfing: usually too small a group, too bright, or not enough cover. Add plants, dim the lights, and bump the school size.
• Faded look and clamped fins: commonly water swings, bullying, or poor diet variety. Check temperature stability and tankmate behavior.
• Fin damage: often nipping from other fish. Separate the culprit or re-home; clean water helps fins recover.
• Ich and other common parasites: they can get the usual community stuff. Quarantine new fish and treat early if you see white spots or flashing.
• Wasting/skinny fish: internal parasites can happen in tetras. If one keeps losing weight while still eating, consider isolating and treating.