Photo: User:Haplochromis (CC BY-SA 3.0) — via Wikimedia Commons
Mexican Tetra (Astyanax mexicanus)
The only aquarium fish with both a sighted river form and a famous eyeless cave form — and both are surprisingly easy to keep.
Will it live with a Mexican Tetra?
We compare each fish against your mexican tetra on temperament, size, water parameters and swimming zone. Set your tank size and filter the results.
- Agassiz's Corydoras✅ CompatiblePeaceful · 6 cm · Easy care · 22–28 °C (72–82 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 22–25 °C — no size, zone or temperament conflicts.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Agassiz's Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Bearded Corydoras✅ CompatiblePeaceful · 10 cm · Medium care · 18–24 °C (64–75 °F)
- Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Bearded Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Black Kuhli Loach✅ CompatiblePeaceful · 8 cm · Easy care · 23–28 °C (73–82 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 23–25 °C — no size, zone or temperament conflicts.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Blood Red Tiger Pleco✅ CompatiblePeaceful · 6 cm · Medium care · 24–29 °C (75–84 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 24–25 °C — no size, zone or temperament conflicts.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Bolivian Ram✅ CompatiblePeaceful · 8 cm · Medium care · 24–28 °C (75–82 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 24–25 °C — no size, zone or temperament conflicts.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Bristlenose Pleco✅ CompatiblePeaceful · 12 cm · Easy care · 23–30 °C (73–86 °F)
- Compatible on the things that matter: shared water near 23–25 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Burmese Loach✅ CompatiblePeaceful · 9 cm · Easy care · 22–28 °C (72–82 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 22–25 °C — no size, zone or temperament conflicts.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Butterfly Hillstream Loach✅ CompatiblePeaceful · 6 cm · Hard care · 18–24 °C (64–75 °F)
- Compatible on the things that matter: shared water near 18–24 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Clown Pleco✅ CompatiblePeaceful · 9 cm · Medium care · 24–28 °C (75–82 °F)
- Compatible on the things that matter: shared water near 24–25 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Corydoras Catfish✅ CompatiblePeaceful · 6.5 cm · Easy care · 22–26 °C (72–79 °F)
- Compatible on the things that matter: shared water near 22–25 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Corydoras Catfish in a shoal of 6+ or it gets stressed and nippy.
- Dwarf Chain Loach✅ CompatiblePeaceful · 6 cm · Medium care · 24–29 °C (75–84 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 24–25 °C — no size, zone or temperament conflicts.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Dwarf Chain Loach in a shoal of 6+ or it gets stressed and nippy.
- Elegant Cory✅ CompatiblePeaceful · 6 cm · Easy care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–25 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Elegant Cory in a shoal of 6+ or it gets stressed and nippy.
- False Julii Corydoras✅ CompatiblePeaceful · 6 cm · Easy care · 22–26 °C (72–79 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 22–25 °C — no size, zone or temperament conflicts.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep False Julii Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Giant Kuhli Loach✅ CompatiblePeaceful · 12 cm · Easy care · 24–30 °C (75–86 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 24–25 °C — no size, zone or temperament conflicts.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Kuhli Loach✅ CompatiblePeaceful · 10 cm · Easy care · 24–30 °C (75–86 °F)
- Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Leopard Frog Pleco✅ CompatiblePeaceful · 9 cm · Medium care · 25–30 °C (77–86 °F)
- Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Pantanal Corydoras✅ CompatiblePeaceful · 8 cm · Medium care · 22–27 °C (72–81 °F)
- Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Pantanal Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Peppered Corydoras✅ CompatiblePeaceful · 7 cm · Easy care · 18–26 °C (64–79 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 18–25 °C — no size, zone or temperament conflicts.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Peppered Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Porthole Catfish✅ CompatiblePeaceful · 10 cm · Easy care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–25 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Spotfin Corydoras✅ CompatiblePeaceful · 6.5 cm · Easy care · 22–26 °C (72–79 °F)
- Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Spotfin Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Spotted Corydoras✅ CompatiblePeaceful · 7 cm · Easy care · 22–27 °C (72–81 °F)
- Compatible on the things that matter: shared water near 22–25 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Spotted Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Spotted Rubbernose Pleco✅ CompatiblePeaceful · 12 cm · Medium care · 20–26 °C (68–79 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 20–25 °C — no size, zone or temperament conflicts.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Sterbai Corydoras✅ CompatiblePeaceful · 6.5 cm · Medium care · 24–30 °C (75–86 °F)
- Compatible on the things that matter: shared water near 24–25 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Sterbai Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Striped Eel Loach✅ CompatiblePeaceful · 12 cm · Medium care · 24–28 °C (75–82 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 24–25 °C — no size, zone or temperament conflicts.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Afra Cichlid⚠️ With cautionSemi-aggressive · 10 cm · Medium care · 24–28 °C (75–82 °F)
- Mexican Tetra and Afra Cichlid can both be territorial; doable with space and dense planting, but watch for chasing.
- Your 110 L tank is below the ~150 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Afra Cichlid in a shoal of 6+ or it gets stressed and nippy.
- Agassiz's Dwarf Cichlid⚠️ With cautionSemi-aggressive · 9 cm · Medium care · 24–30 °C (75–86 °F)
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Bandit Cichlid⚠️ With cautionSemi-aggressive · 9 cm · Medium care · 22–26 °C (72–79 °F)
- Mexican Tetra and Bandit Cichlid can both be territorial; doable with space and dense planting, but watch for chasing.
- Your 110 L tank is below the ~150 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Bandit Cichlid in a shoal of 6+ or it gets stressed and nippy.
- Brichardi Cichlid⚠️ With cautionSemi-aggressive · 9 cm · Medium care · 24–28 °C (75–82 °F)
- Mexican Tetra and Brichardi Cichlid can both be territorial; doable with space and dense planting, but watch for chasing.
- Your 110 L tank is below the ~120 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Brilliant Rasbora⚠️ With cautionPeaceful · 9 cm · Easy care · 22–28 °C (72–82 °F)
- Expect Mexican Tetra to harass Brilliant Rasbora at times; give dense cover and watch them at feeding.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Brilliant Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Clown Rasbora⚠️ With cautionPeaceful · 10 cm · Medium care · 23–28 °C (73–82 °F)
- Mexican Tetra is a notorious fin-nipper — even though Clown Rasbora is larger, an active shoal will harass its trailing fins. Only safe in a full group of 6+ with plenty of cover.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Clown Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Daffodil Cichlid⚠️ With cautionSemi-aggressive · 10 cm · Medium care · 23–27 °C (73–81 °F)
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Your 110 L tank is below the ~120 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Electric Yellow Cichlid⚠️ With cautionSemi-aggressive · 10 cm · Medium care · 23–26 °C (73–79 °F)
- Mexican Tetra and Electric Yellow Cichlid can both be territorial; doable with space and dense planting, but watch for chasing.
- Your 110 L tank is below the ~200 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Giant Danio⚠️ With cautionPeaceful · 10 cm · Easy care · 20–27 °C (68–81 °F)
- Giant Danio is slow and long-finned; a busy mexican tetra shoal tends to nip at it. Keep mexican tetra in a proper group of 6+ and watch them closely.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Giant Danio in a shoal of 6+ or it gets stressed and nippy.
- Golden Wonder Killifish⚠️ With cautionSemi-aggressive · 10 cm · Easy care · 22–28 °C (72–82 °F)
- Mexican Tetra and Golden Wonder Killifish can both be territorial; doable with space and dense planting, but watch for chasing.
- Golden Wonder Killifish is slow and long-finned; a busy mexican tetra shoal tends to nip at it. Keep mexican tetra in a proper group of 6+ and watch them closely.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keyhole Cichlid⚠️ With cautionPeaceful · 10 cm · Easy care · 22–28 °C (72–82 °F)
- Mexican Tetra is a notorious fin-nipper — even though Keyhole Cichlid is larger, an active shoal will harass its trailing fins. Only safe in a full group of 6+ with plenty of cover.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Kribensis⚠️ With cautionSemi-aggressive · 10 cm · Easy care · 24–27 °C (75–81 °F)
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Molly⚠️ With cautionPeaceful · 10 cm · Easy care · 23–28 °C (73–82 °F)
- Molly is slow and long-finned; a busy mexican tetra shoal tends to nip at it. Keep mexican tetra in a proper group of 6+ and watch them closely.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Silver Tetra⚠️ With cautionPeaceful · 9 cm · Easy care · 24–28 °C (75–82 °F)
- Mexican Tetra and Silver Tetra are close in size, but the semi-aggressive one tends to dominate — add silver tetra in a group to spread the pressure.
- Your 110 L tank is below the ~115 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Keep Silver Tetra in a shoal of 6+ or it gets stressed and nippy.
- Thick-lipped Gourami⚠️ With cautionPeaceful · 9 cm · Easy care · 22–28 °C (72–82 °F)
- Expect Mexican Tetra to harass Thick-lipped Gourami at times; give dense cover and watch them at feeding.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Zebra Loach⚠️ With cautionPeaceful · 9 cm · Medium care · 23–26 °C (73–79 °F)
- Your 110 L tank is below the ~115 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Alligator Gar⛔ Not recommendedAggressive · 250 cm · Hard care · 24–28 °C (75–82 °F)
- Mexican Tetra and Alligator Gar are both territorial and at least one is outright aggressive — expect serious fighting.
- Alligator Gar (250 cm) is big enough to swallow the 9 cm Mexican Tetra whole.
- Mexican Tetra is a notorious fin-nipper — even though Alligator Gar is larger, an active shoal will harass its trailing fins. Only safe in a full group of 6+ with plenty of cover.
- Your 110 L tank is below the ~3785 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Clown Knifefish⛔ Not recommendedAggressive · 90 cm · Hard care · 24–28 °C (75–82 °F)
- Two assertive fish, one genuinely aggressive: Mexican Tetra and Clown Knifefish will hold territory and clash.
- Size gap is too large (90 vs 9 cm): Clown Knifefish will treat Mexican Tetra as food.
- Your 110 L tank is below the ~750 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Fire Eel⛔ Not recommendedSemi-aggressive · 100 cm · Medium care · 24–28 °C (75–82 °F)
- Size gap is too large (100 vs 9 cm): Fire Eel will treat Mexican Tetra as food.
- Mexican Tetra and Fire Eel can both be territorial; doable with space and dense planting, but watch for chasing.
- Your 110 L tank is below the ~380 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Koi⛔ Not recommendedPeaceful · 90 cm · Medium care · 4–28 °C (39–82 °F)
- Koi (90 cm) is big enough to swallow the 9 cm Mexican Tetra whole.
- Koi is slow and long-finned; a busy mexican tetra shoal tends to nip at it. Keep mexican tetra in a proper group of 6+ and watch them closely.
- Your 110 L tank is below the ~3800 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Redtail Catfish⛔ Not recommendedAggressive · 120 cm · Hard care · 24–27 °C (75–81 °F)
- Mexican Tetra and Redtail Catfish are both territorial and at least one is outright aggressive — expect serious fighting.
- Redtail Catfish (120 cm) is big enough to swallow the 9 cm Mexican Tetra whole.
- Your 110 L tank is below the ~5700 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Spotted Gar⛔ Not recommendedAggressive · 90 cm · Hard care · 18–26 °C (64–79 °F)
- Mexican Tetra and Spotted Gar are both territorial and at least one is outright aggressive — expect serious fighting.
- Spotted Gar (90 cm) is big enough to swallow the 9 cm Mexican Tetra whole.
- Mexican Tetra is a notorious fin-nipper — even though Spotted Gar is larger, an active shoal will harass its trailing fins. Only safe in a full group of 6+ with plenty of cover.
- Your 110 L tank is below the ~600 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Wels Catfish⛔ Not recommendedAggressive · 300 cm · Hard care · 15–25 °C (59–77 °F)
- Mexican Tetra and Wels Catfish are both territorial and at least one is outright aggressive — expect serious fighting.
- Size gap is too large (300 vs 9 cm): Wels Catfish will treat Mexican Tetra as food.
- Your 110 L tank is below the ~20000 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
- Wolf Cichlid⛔ Not recommendedAggressive · 72 cm · Hard care · 24–30 °C (75–86 °F)
- Two assertive fish, one genuinely aggressive: Mexican Tetra and Wolf Cichlid will hold territory and clash.
- Mexican Tetra is bite-sized to a 72 cm predatory wolf cichlid — it will be eaten.
- Wolf Cichlid is slow and long-finned; a busy mexican tetra shoal tends to nip at it. Keep mexican tetra in a proper group of 6+ and watch them closely.
- Your 110 L tank is below the ~760 L this pairing really wants — crowding raises aggression.
- Keep Mexican Tetra in a shoal of 6+ or it gets stressed and nippy.
Compatibility is computed from each species' care data — a strong starting point, not a guarantee. Individual temperament varies, so always introduce new fish slowly and watch them.
Mexican Tetra care specs
- Care level
- Easy
- Breeding
- Easy
- Max size
- 9 cm (3.5 in)
- Min tank size
- 110 L (29.1 gal)
- Temperature
- 18–25 °C (64–77 °F)
- pH
- 6.5–8
- Hardness
- 5–25 dGH
- Lifespan
- 3–8 years
- Diet
- Omnivore
- Swim level
- Middle
- Group size
- 6+ (shoaling)
- Family
- Characidae
- Origin
- North and Central America — rivers of Mexico and Texas (sighted form); limestone caves of Mexico (blind cave form)
What is a Mexican Tetra?
The Mexican Tetra (Astyanax mexicanus) is a mid-sized, hardy characin with a genuinely unique story: it is one of the very few vertebrates that exists simultaneously as a fully-sighted river-dwelling form and a pale, eyeless cave-dwelling form — and both are the same species. That evolutionary split makes it a favourite of biology teachers and curious fishkeepers alike, but day-to-day it is simply a fast-moving, active, sociable fish that adapts well to a wide range of conditions.
The sighted river form is silver-bodied with a faint pink or golden flush and a dark stripe running from the mid-body toward the tail. The blind cave form (cavefish) is a muted, translucent pink-white — no pigment, no functional eyes, just smooth skin where the orbits once were. Both grow to around 9 cm (3.5 in) and share the same care requirements. They are among the most undemanding fish in the characin family, tolerating cooler water, harder conditions and a broader pH range than most of their tropical cousins.
Where do Mexican Tetras come from?
The sighted form is native to rivers and streams in Mexico and southern Texas, including the Rio Grande drainage and several coastal rivers along the Gulf of Mexico. It lives in clear to moderately turbid water over gravel or sandy substrates, often in fast to moderately flowing sections. The blind cave form is found exclusively in the limestone cave systems of the Sierra de El Abra and Micos regions of Tamaulipas and San Luis Potosí, Mexico — permanent underground rivers and cave pools where there is no light and food is scarce and unpredictable.
In captivity the distinction barely matters for care: both thrive in similar water chemistry, though the blind cave form is arguably even tougher given the feast-or-famine conditions it evolved in. The species’ range from roughly 18–25 °C (64–77 °F) natural water temperatures means it handles cooler tanks that would stress a typical tropical fish.
What size tank does a Mexican Tetra need?
The minimum recommended tank size is 110 L (29 gal), and that is genuinely the minimum for a shoal of six — the smallest group that lets these fish express normal behaviour. Mexican Tetras are active, fast swimmers that use the full length of the tank, so floor footprint matters more than height. A 120 cm (48 in) long tank of standard depth is a good starting point.
Open swimming space in the centre and middle column is important, with plants, driftwood or rocks toward the sides and back to give fish a sense of territory and shelter. A tight-fitting lid is advisable — these are agile jumpers, especially in the dark when the blind cave form in particular explores its boundaries. Moderate to strong filtration is well-tolerated and mimics the current of their native rivers.
What water parameters do Mexican Tetras need?
One of this species’ best attributes is its tolerance of imperfect or variable water:
- Temperature: 18–25 °C (64–77 °F). This cooler range means they can work in temperate or subtropical setups and do not strictly require a heater in many climates, though a heater set to 22–24 °C keeps conditions stable.
- pH: 6.5–8.0. This wide range covers most unmodified tap water in the world.
- Hardness: 5–25 dGH. Soft through moderately hard water is accepted without issues.
Stability is more important than chasing any particular number within those ranges. Cycle the tank fully before introducing fish, perform regular water changes of 20–25% weekly, and avoid sudden temperature or chemistry swings. The blind cave form is particularly robust but, like all fish, does not tolerate rapid change well.
What do Mexican Tetras eat?
Mexican Tetras are omnivores with a strong opportunistic streak — in the wild the cavefish in particular eats almost anything organic it can detect. In the aquarium, a quality flake or micro-pellet food as a daily staple works well, rotated with:
- Frozen or live bloodworm and brine shrimp
- Daphnia or tubifex
- Finely chopped earthworm or insect-based foods
Feed small amounts twice a day and remove uneaten food promptly. The blind cave form finds food by sensing vibrations and following scent, so it generally keeps pace with sighted tank mates without issue. Avoid overfeeding — this species will eat past satiation, and excess waste in a 110 L tank degrades water quality quickly.
Are Mexican Tetras aggressive — and what fish can live with them?
Mexican Tetras are semi-aggressive, meaning they are generally peaceful in normal conditions but can become nippy — particularly at feeding time or if kept in too small a group. The blind cave form can inadvertently mouth-nip tank mates while searching for food rather than out of genuine aggression, but the effect on a long-finned neighbour is the same.
The best mitigation is a proper shoal: six or more Mexican Tetras distribute attention within the group and reduce fixation on any single tank mate. Good companions are robust, similarly-sized community fish — barbs, larger danios, rainbow fish, rainbowfish, cichlids of comparable size, and other medium tetras. Avoid slow, long-finned species such as fancy guppies or bettas, and very small fish that could become a snack.
For a full list of tested pairings, see Mexican Tetra tank mates.
How do you tell male and female Mexican Tetras apart?
Sexing Mexican Tetras is straightforward once fish reach adult size. Females are noticeably rounder and deeper-bodied, particularly when carrying eggs — a gravid female looks almost plump compared to her tank mates. Males are slimmer and more streamlined. In the sighted form, males may show a slightly more defined lateral stripe, but the body shape difference is the most reliable indicator. In the blind cave form the same rule applies: females are visibly fuller-bodied ahead of a spawn.
How do Mexican Tetras breed?
Mexican Tetras are egg scatterers and among the easiest tetras to breed — hence the Easy breeding difficulty rating. Spawning often happens without any deliberate encouragement; a healthy, well-fed group in a stable tank will spawn periodically on their own.
For deliberate breeding, condition a pair or small group with live or frozen foods for a week or two, then move them to a shallow, bare-bottom breeding tank with fine-leafed plants or a spawning mop. Slightly cooler water (around 20 °C / 68 °F) can trigger spawning. The female scatters small, adhesive eggs among plants; the male fertilises as they fall. Remove the adults immediately after spawning — both parents will eat the eggs. Fry hatch in 24–36 hours and become free-swimming after another two to three days. Start feeding with infusoria or commercial fry food, then transition to baby brine shrimp as they grow.
What are common Mexican Tetra diseases?
Mexican Tetras are hardy and not especially disease-prone when water quality is maintained, but they share the common characin vulnerabilities:
- Ich (white spot) — small white granules on the body and fins, usually triggered by temperature stress or introducing new fish without quarantine.
- Fin rot — ragged or receding fin edges, almost always a sign of poor water quality or bacterial infection following a nip wound.
- Neon tetra disease / microsporidian infection — fading patches of colour and muscular wasting; no cure, so prevention (buying from reputable sources, quarantine) is critical.
- Velvet (Oodinium) — a dusty gold or rust-coloured film; more common in cooler or fluctuating-temperature tanks.
Prevention is straightforward: maintain good filtration, do not overstock, quarantine all new arrivals for two to three weeks, and avoid dramatic temperature swings. The blind cave form is equally susceptible — it lacks eyes but not immune vulnerability.
Health note: confirming a specific disease visually before treatment is always the right first step. Consult a reputable veterinary or fish-health resource to verify symptoms before medicating.
How long do Mexican Tetras live?
With good care, Mexican Tetras live 3–8 years — the sighted river form tends toward the middle of that range, while robust individuals in well-maintained setups can reach the upper end. The blind cave form has similar longevity under aquarium conditions. As with most aquarium fish, the quality of water, diet and tank mates has far more influence on lifespan than any other variable. A shoal kept in a correctly sized, well-filtered tank with a varied diet will give you the best chance of seeing the full 8 years.
Frequently asked questions
Are Mexican Tetras fin-nippers?
They can be, particularly at feeding time — the blind cave form searches for food with its mouth and may accidentally nip tank mates. Keep them with robust, similarly-sized fish and avoid long-finned or very slow species. A proper shoal of six or more spreads any attention and reduces individual harassment.
Can I keep the sighted and blind cave forms together?
Yes, they are the same species and interbreed freely. Many hobbyists mix them in the same tank without issues. The blind cave form navigates by sensing vibrations and water pressure, so it holds its own even without sight.
What you need to keep a mexican tetra
The baseline is a heated, filtered 110 L+ tank: a reliable heater to hold 18–25 °C (64–77 °F), a gentle filter that won't batter a mexican tetra in the current, and a tight-fitting lid. Cycle the tank fully before adding any fish.
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