Four Eyed Fish Anableps Care Guide: Surface Brackish Species
Anableps is the only fish in the trade with eyes truly divided in two — a structural adaptation for simultaneously seeing above and below the water surface. This four eyed fish anableps care guide from Gensou Aquascaping at 5 Everton Park covers Anableps anableps, a 25cm Central American brackish live-bearer that lives glued to the surface, swimming in tight schools across mangrove flats. The species needs a long, shallow tank that few keepers initially plan for, and respects almost no other husbandry instinct from standard fishkeeping.
Quick Facts
- Scientific name: Anableps anableps
- Adult size: 20 to 30cm
- Minimum tank: 200 litres in a long, shallow footprint (120 by 50cm minimum)
- Temperature: 24 to 28°C — Singapore ambient suitable
- Salinity: SG 1.005 to 1.020, adults best at 1.010 to 1.015
- Schooling: minimum five, prefer seven or more
- Live-bearer with internal fertilisation, 5 to 12 large fry per brood
The Divided Eye
Each eye has two pupils, two corneas and two retinal regions, allowing simultaneous focus in air (above the water line) and in water (below it). The fish swims with the eyeline exactly at the surface, scanning for insect prey above and predators below. This anatomy drives the entire husbandry approach: tanks must be wide and shallow with a long open swimming surface and absolutely no risk of impalement on emergent hardscape.
Tank Setup — Shape Matters More Than Volume
Forget tall display tanks. Anableps need length and width with relatively shallow water — 30 to 40cm depth is plenty. A 120 by 50 by 35cm tank holds about 200 litres and provides the long surface run a school requires. Substrate is a free choice; aragonite sand suits the brackish setup. Hardscape should sit low and smooth, with mangrove roots positioned underwater rather than emerging. Floating plants such as Amazon frogbit (in low salinity) or even artificial mangrove leaves give the school overhead cover without breaking the surface plane.
A tight, gap-free lid is non-negotiable — anableps are surface dwellers and will jump or push through any opening. Filtration should be a sump or oversized canister positioned to give gentle surface flow, not a rough turbulent return.
Salinity Management
Wild anableps live in low-salinity mangrove flats and tidal mudflats from southern Mexico to Brazil. They tolerate full freshwater for short periods and full marine salinity briefly, but thrive in true brackish conditions. Use a refractometer and target SG 1.010 to 1.015 for adults, slightly lower for juveniles. Wholesalers often arrive shipping in near-freshwater; ramp salinity 0.002 per week after acclimation.
Schooling and Surface Behaviour
A school of one or two anableps becomes nervous, refuses to feed and rarely lasts a year. Five or more produces the synchronised surface-cruising display the species is known for. The school spends nearly all daylight hours in the top 5cm of the tank, peering above and below. Provide enough surface area that the group is not constantly bumping into each other.
Feeding
Wild anableps eat insects from the air-water interface, supplemented with crustaceans and small fish below. Captive specimens accept floating pellets, freeze-dried krill, frozen bloodworm, mosquito larvae, small chopped prawn and the occasional live cricket or fly. Sinking food is largely ignored — they rarely look down to feed. Two small feeds per day for juveniles, once daily for adults.
Live-Bearing Reproduction
Anableps are unusual live-bearers. The male’s gonopodium curves either left or right, and the female’s genital opening curves the corresponding direction — the population effectively splits into “lefty” and “righty” mating compatibility groups. Internal fertilisation produces 5 to 12 large fry (3 to 5cm) after a 90-day gestation. Fry are immediately surface-oriented and accept the same foods as adults if reduced to fine pieces. Separate from adults to prevent predation.
Tank Mates
Best kept species-only, especially for breeding. Compatible companions for display tanks include other low-position brackish species — knight gobies, bumblebee gobies, mollies in higher salinity, and small surface-tolerant species that do not compete for the same airline. Avoid scats, monos and other large brackish species which displace anableps from the surface. Pufferfish nip at fins and are unsuitable.
Singapore Sourcing
Anableps is uncommon in Singapore but appears occasionally at specialist brackish-stocking shops in the C328 Clementi cluster and through Carousell from importers, typically $40 to $80 per juvenile. Quality varies; look for fish actively scanning the surface with intact eye membranes and no whitening at the eye margin (a sign of dry-air damage during shipping). Acclimatise carefully with attention to both temperature and salinity.
Common Problems
Eye damage from dry air during transport or low water levels is the most common health issue — once the cornea dries it rarely recovers. Maintain tank water within 5cm of the lid to keep humidity high. Bacterial fin and skin infections appear in tanks kept too fresh long-term. Failure to thrive in deep, narrow tanks is essentially a husbandry mismatch and only solves with a tank reshape. Always plan the footprint before buying the fish.
Related Reading
emilynakatani
Still Have Questions About Your Tank?
Drop by Gensou Aquascaping — most walk-in questions get answered in under 10 minutes by someone who has set up hundreds of tanks.
5 Everton Park #01-34B, Singapore 080005 · Open daily 11am – 8pm
