Four-eyed fish

The four-eyed fish has a slender body and a unique visual organ structure that protrudes above the head. Each eye is divided by a horizontal band of tissue into two parts, allowing the fish to see both above and below the water simultaneously. Adults reach a length of 20–26 cm, with females being noticeably larger than males. The body coloration is brownish with a golden stripe along the back and several blue or purple lines on the sides. The fish's mouth is wide, with fleshy lips and teeth for holding prey. The caudal fin is fan-shaped, and the dorsal fin is strongly shifted towards the posterior part of the body. In males, the anal fin is modified into a specialized copulatory organ — the gonopodium. External sexual characteristics also include an asymmetrical genital structure, which is a characteristic feature of this species.

The species inhabits the northern coast of South America, from Trinidad and Venezuela to the Amazon delta in Brazil, including Guyana, Suriname and French Guiana. Their preferred habitats are river estuaries that flow into the sea. The Four-eyed fish spends a significant part of its life in the upper layers of the water, where it hunts small insects and various crustaceans.

This fish is characterized by a peaceful schooling nature, but it should be noted that it may prey on smaller tank mates if they can fit into its mouth. Four-eyed fish feel great in the company of their own kind; optimal groups consist of 5–6 individuals. The species is compatible with brackish water inhabitants that live in the middle or bottom layers of the aquarium.

pH and GH values do not play a critical role for this species; it is much more important to maintain a certain level of water salinity. When preparing water, it is recommended to dissolve salt in a proportion of 1 gram per 1 liter. Simple airlift filters and a reliable heater will suffice for equipment. The lighting system should provide moderate light intensity. It is advisable to fill the aquarium to half or three-quarters of its volume and keep it tightly covered to prevent the fish from jumping out. Rooted plants that can tolerate saline water are preferred for decoration. Four-eyed fish require sufficient space for free swimming. If plants grow too large and begin to cover the water surface, they should be trimmed or cut back. The choice of substrate and decorative elements for the lower tier of the aquarium is at the discretion of the aquarist, as this fish shows minimal interest in what happens at the bottom.

Since the Four-eyed fish is a carnivorous species, appropriate feeding must be provided for its maintenance in a home aquarium. The diet can include live, frozen, dry, or fresh foods, such as bloodworms, mosquito larvae, large artemia, and others. It is important to remember that the fish will only consume food if it is on the water surface.

Reproduction of this species occurs quite quickly and does not require special effort from the aquarist. Fry appear fully formed, bypassing the egg stage. The only important condition is that after the young appear, they must be moved to a separate tank, as adult individuals may eat their own offspring.

Four-eyed fish are very sensitive to bacterial infections, which are sometimes difficult to treat. The main cause of these problems often lies in the unstable salt concentration in the water, caused by evaporation.

When choosing four-eyed fish in a store, it is important to assess the overall activity of the individuals and the condition of their skin, which should be free of plaque, spots, or damage. Healthy fish stay in a school, show interest in the water surface, and react actively to movement. Avoid specimens with signs of emaciation, sunken bellies, or damaged fins. Given the specifics of the species, check the fish's eyes: they should be clear, without cloudiness, and clearly divided into two functional zones. Since four-eyed fish are schooling fish, it is recommended to purchase a group of 6–10 individuals at once to reduce stress during adaptation to new conditions. Ask the seller what type of food the fish are accustomed to in the store.