Bigeye cichlid
Acaronia nassa
Bigeye cichlids exhibit a sleek body with striking iridescent blue and yellow markings and prominent, large eyes, enhancing their underwater visibility.
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About the Bigeye cichlid
Acaronia nassa is that oddball Amazon cichlid with the huge eyes and a big, suction-style mouth - it is built to ambush little fish in dim, tannin-stained water. In the tank it is usually more chill than its predator vibe suggests, but anything that fits in its mouth is absolutely on the menu.
Also known as
Quick Facts
Size
16 cm SL
Temperament
Semi-aggressive
Difficulty
Intermediate
Min Tank Size
75 gallons
Lifespan
8-12 years
Origin
South America
Diet
Carnivore/piscivore - insect larvae and small fish; in aquariums takes pellets, flakes, and frozen foods
Water Parameters
25-28°C
7-7.5
12-15 dGH
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Calculate heater sizeCare Notes
- Give them a big footprint tank with cover - think 75g+ for an adult, sand or fine gravel, chunky driftwood, and a couple of caves so they can claim a spot without seeing everyone all the time.
- They do best in warm, soft-ish water: about 78-84F, pH roughly 6.0-7.2, and keep nitrates low because they get sulky and hole-up when the water gets dirty.
- These guys are messy eaters, so run strong filtration and do regular water changes; if you see stringy poop or they stop coming out to eat, check your maintenance routine first.
- Feed like a predator but not like a garbage can: quality pellets as the staple, then rotate in shrimp, krill, earthworms, and the occasional piece of fish - skip feeder goldfish/rosies because they bring parasites and fat problems.
- Tankmates need to be sturdy and not snack-sized: big tetras (silver dollars), larger catfish (big plecos, pimelodids), and other similarly sized cichlids can work, but avoid small fish and super aggressive brawlers that never back off.
- They get extra pushy as they mature, especially if they pair up; if one fish starts camping a corner and chasing everything, add more line-of-sight breaks or be ready to separate.
- Breeding is classic cichlid stuff: they like a flat rock or cleared pit, and the parents will guard hard - if you want fry, move other fish out or the pair will turn the whole tank into a no-go zone.
Compatibility
Good Tankmates
- Other medium-large South American cichlids with similar attitude (severums, uaru, smaller/medium geos) - best if you grow them up together and give lots of wood/rocks to break lines of sight
- Tough dither fish that stay out of the way (silver dollars, larger headstanders) - they help keep the bigeye less jumpy and spread out aggression
- Armor-plated bottom crew (bigger plecos like a common/sailfin, or a chunky Panaque) - they can handle the occasional "get out of my cave" shove
- Larger catfish that mind their business (pictus-type cats, Raphael/talking cats, decent-sized Pimelodus) - good as long as everyone is too big to swallow and you provide hiding spots
- Big, sturdy tetras/barbs that are fast and not finny (Congo tetras, larger lemons are iffy, better stuff like Buenos Aires tetras if your water matches) - only in a roomy tank so they can stay in a group
- A bonded pair of bigeyes or a careful single - pairs can work, but once they decide to spawn they will claim a whole zip code, so plan extra space and backup dividers
Avoid
- Tiny snack-sized fish (neons, rummynose, small livebearers) - adult bigeyes are opportunistic and will eventually test the "fits in my mouth" rule
- Slow fish with fancy fins (angelfish, longfin gouramis, fancy guppies) - they get harassed, nipped, and stressed when the bigeye starts doing cichlid patrols
- Hyper-nippy or super aggressive brawlers (tiger barbs in small groups, some Central American bruisers like jaguars/convicts, mean peacock bass) - turns the tank into a nonstop turf war
- Other bottom-territory cichlids in tight quarters (JDs, some large acara types, cranky geophagus kept too small) - cave fights are where bigeyes really throw hands
Where they come from
Bigeye cichlids (Acaronia nassa) are South American fish from the Amazon and nearby river systems. Think slow-moving, tannin-stained waters with leaf litter, branches, and patchy plants. They are the kind of cichlid that looks like it is always watching you, and honestly... they kind of are.
Acaronia nassa often shows up as a bycatch import. Healthy ones are worth waiting for - avoid fish with sunken bellies, clamped fins, or that "hanging in the corner" look.
Setting up their tank
Give them space and structure. They are not hyper swimmers, but they are big-bodied and territorial once settled. I have had the best luck treating them like a large, thoughtful ambush cichlid: open area to cruise, plus plenty of visual breaks so they do not feel like they have to own the whole tank.
- Tank size: I would start at 75 gallons for one adult. For a pair or a community with other big fish, 120+ is way less stressful.
- Filtration: strong and steady. They eat meaty foods and the tank gets dirty fast.
- Temp: mid to upper 70s F is a comfortable zone for them (around 75-80F).
- pH and hardness: they adapt, but slightly acidic to neutral water is where I have seen the best appetites and color.
- Substrate: sand or smooth gravel. They are not big diggers like some cichlids, but they do mouth and sift.
- Decor: driftwood, rock piles that cannot shift, and big chunks of cover. Caves help, but line-of-sight breaks help more.
Use tall pieces of wood or plants to split the tank into zones. It cuts down on posturing, especially if you keep them with other cichlids.
They can jump, especially when new or spooked. A tight lid saves you heartbreak.
What to feed them
These are predators. Mine were happiest on a mix of quality pellets and frozen foods. The trick is keeping them in good shape without turning them into greasy footballs. They will beg and they will act like they have never been fed in their life.
- Staples: sinking carnivore cichlid pellets, larger granules, or sticks
- Frozen: shrimp, krill, mysis, chopped fish/seafood mixes, bloodworms as a treat
- Occasional: earthworms (rinsed), chopped prawn, live blackworms if you can get them clean
Skip feeder goldfish/rosies. They can bring in parasites and the fat profile is not great. If you use live foods, stick to safer options like worms or home-raised stuff.
Feeding rhythm that worked for me: smaller meals 4-5 days a week, one lighter day, and one day off. They digest better and you get fewer mystery water issues.
How they behave and who they get along with
Bigeye cichlids are a mix of calm and bossy. They are not nonstop brawlers, but they do not back down once they pick a spot. Most of the time mine would just hover and stare, then suddenly decide a fish was too close and do a quick charge.
- Best tankmates: sturdy, similarly sized fish that are not easily bullied
- Good options: big tetras (silver dollars, larger characins), robust catfish (plecos, big pimelodids with caution), medium-large peaceful cichlids that can hold their own
- Avoid: small fish (they will be snacks), slow fancy fins, and super-aggressive cichlids that never stop pushing
If you are trying a community, add the Bigeye last. It helps keep them from claiming the whole tank as "their" tank from day one.
They also do better with a little "background activity". A tank with a few active midwater fish can make them less skittish, which means fewer random panic dashes into the glass.
Breeding tips
Breeding is doable but not something I would call casual. Sexing them is not straightforward, and a random male-female pair can still decide they hate each other. If you want a pair, raising a group of juveniles and letting them sort it out is the least painful route.
- Give them flat surfaces or broad leaves/wood they can use as a spawning site
- Keep the tank calm: lots of cover, stable temps, and fewer tankmates during pairing attempts
- Condition with a meaty diet, but do not overfeed
- Be ready to separate fish if the "pair" turns into a beatdown
During spawning and fry guarding, they can flip from mellow to nasty overnight. If you have other cichlids in the tank, have a backup plan.
Common problems to watch for
Most issues I have seen with Bigeyes come from two things: dirty water from heavy feeding, and stress from bad tankmate choices. They are tougher than they look, but they do not handle chaos well.
- Hole-in-the-head or pitting: often tied to long-term water quality issues and diet. Clean water and a varied diet help a lot.
- Bloat/constipation: usually from overfeeding rich foods. Back off, add a fasting day, and keep pellets as a steady base.
- Ich after new arrivals: they can pick it up easily if you add fish without quarantine.
- Fin damage: from territorial scraps. This is usually a stocking/layout issue, not a medicine issue.
- Spooking and glass surfing: common in bare tanks or bright tanks with no cover
Weekly water changes make a bigger difference with this species than people expect. Meaty foods plus a big cichlid body equals fast nitrate creep.
If a fish stops eating and starts hiding with a darkened color, do not wait it out. Check ammonia/nitrite first, then watch for bullying. These guys can go downhill fast if something is off.
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