Pacific Four-Eyed Fish

1) Where they come from

Pacific four-eyed fish (Anableps dowei) come from the Pacific side of Central America, hanging around river mouths, mangroves, and coastal lagoons. They live right in that messy “half fresh, half salt” zone where tides and rain keep changing things.

They’re surface cruisers built for shallow water. The famous “four eyes” thing is basically two pupils per eye so they can watch above and below the waterline at the same time. Super cool, and it explains a lot about how you need to set them up.

2) Setting up their tank

Think “big, wide, and shallow-ish” rather than tall. These fish use the top few inches of water like it’s their whole world, and they’re fast. A long tank with tons of surface area makes life easier for you and less stressful for them.

• Tank size: I wouldn’t bother under 75 gallons for a group; bigger is honestly better because they’re constant movers
• Footprint matters: long tanks beat tall tanks every time
• Leave open swimming room at the surface—don’t turn the top into a plant jungle

Brackish water is non-negotiable. I’ve seen people try to “ease them in” and then keep them too fresh long-term, and the fish just never looks right—more sickness, worse appetite, shorter lifespan. Mix your salt with a marine salt mix (not table salt), and use a hydrometer or refractometer so you’re not guessing.

• Salinity: aim for true brackish (many keep them around SG ~1.005–1.012), and keep it steady
• Temperature: mid-to-upper 70s°F works well for most setups (around 24–27°C)
• Filtration: strong bio-filtration plus good surface agitation; they like clean, oxygen-rich water
• Flow: moderate is fine, but don’t blast the surface so hard they can’t cruise

Decor-wise, give them edges and structure without cluttering the surface. Mangrove-style roots, smooth wood, and rockwork along the back/sides works great. Sand is my go-to—easy to clean, looks natural, and they don’t mind it.

3) What to feed them

They’re hungry surface feeders with a big mouth and an even bigger opinion about food. Mine did best with a mix of meaty foods and quality prepared options. If you only feed one thing, they either get picky or start looking a bit rough over time.

• Staples: floating pellets or sticks made for brackish/marine carnivores
• Frozen: krill, mysis, chopped shrimp, bloodworms (as a treat), squid bits
• Live treats: insects (like small crickets), mosquito larvae where safe/clean
• Occasional: blanched veg or algae-based foods if they’ll take it (some do, some don’t)

Feed from the top and watch them eat. They’re bold, so food disappears fast, but weaker fish can get bullied off meals. I like multiple small feeds instead of one huge dump—less waste, and everyone gets a shot.

4) Behavior and tankmates

They’re active, nosy, and always patrolling the surface. If you keep just one, it can get weirdly skittish or overly bossy. A small group is way more natural, but you need the space because they bicker and chase.

• Keep in a group if your tank is big enough (5–6+ is a nice target)
• Expect pecking-order drama, especially at feeding time
• They’re not “mean” in a cichlid way, but they will harass slower fish

Tankmates need to handle brackish water and not compete for the exact same surface lane. You want fish that hang mid-water or bottom, are quick enough to avoid being pestered, and aren’t tiny enough to be viewed as snacks.

• Often workable: brackish monos, scats (in big tanks), brackish gobies, some larger brackish tolerant rainbowfish-type options depending on salinity
• Use caution with: archerfish (surface competition), puffers (fin nipping), anything small enough to fit in their mouth
• Best plan: species tank if you’re new to Anableps—they’re entertaining enough on their own

5) Breeding tips

Breeding is possible, but it’s not a “drop in some plants and hope” situation. They’re livebearers, and the weird part is their plumbing: males have a modified fin (gonopodium) and females have a matching opening—there’s a left-leaning and right-leaning setup, and the fish need to be compatible to mate successfully.

• Start with a group and let them pair off naturally—buying a single “pair” is hit-or-miss
• Keep them well-fed and stable in brackish water; condition with meaty frozen foods
• Give lots of surface room so chased females can get away

If you get fry, the adults may snack on them. A separate grow-out tank in matching brackish water makes life way easier. Fry will take small floating foods and finely chopped frozen pretty quickly if water quality is good.

6) Common problems to watch for

Most issues I’ve seen with Anableps come from three things: wrong salinity, cramped surface space, and lid gaps. Fix those and you’re already ahead of the game.

• Jumping/escaping: the #1 killer—seal every opening
• Chronic stress from small tanks: constant chasing, beat-up fins, poor feeding
• Skin/fin issues from “kinda brackish” water: they do better with consistent, measurable salinity
• Cloudy eyes or injuries: often from bumping lids or rough decor near the surface
• Ich/parasites after new additions: quarantine helps a lot, and remember meds can behave differently in salty water

If your fish hangs back, stops cruising the surface, or starts getting outcompeted at meals, treat it like an early warning. Test the salinity, check ammonia/nitrite, look for bullying, and watch the lid/waterline setup. With Anableps, little setup mistakes show up in their behavior fast.