Porthole Catfish

Dianema longibarbis takes its name from the long barbels around its mouth. Its light brown, slender and elongated body carries scattered small dark spots; the English name "porthole" comes from the spots lined up along the sides being likened to a ship's portholes. The tail fin is translucent and unstriped.

Its close relative Dianema urostriatum has a tail with distinct black-and-white horizontal stripes; this is the easiest way to tell the two species apart. Instead of foraging on the bottom like corydoras, both species usually hover in midwater as a group. Adults reach 8–10 cm.

It lives in the slow-flowing, vegetated waters of the Amazon basin in Peru and Brazil, especially in stretches surrounded by flooded forest. In these areas it is found in small groups among roots and fallen branches. In the rainy season the waters spill into the forest; during this period the fish feed in the flooded areas.

• Volume: at least 120 liters for a group of 4–6; a length of around 100 cm.
• Swimming space: open space in midwater and hiding places such as roots and plants along the sides.
• Light: soft light; floating plants help the fish stay out in the open.
• Water: 22–27°C; soft to moderately hard, clean water, gentle flow.
• Lid: it comes to the surface to gulp air; a covered aquarium is recommended.

Omnivorous. Sinking granules and tablets, frozen bloodworms, brine shrimp and mosquito larvae go down well. It looks for food both in midwater and on the bottom; if other fish are very fast, give an extra feeding in the evening.

Peaceful and calm. It hovers in groups in midwater, often motionless; when threatened it retreats among the roots. It may eat shrimp fry small enough to fit in its mouth.

Good companions: medium-sized peaceful tetras, pencilfish, angelfish, dwarf cichlids, corydoras, peaceful gouramis.

Avoid: aggressive or fin-nipping species, very small fish, constantly darting fast species.

A schooling fish; at least 4, ideally 6 or more individuals. Kept alone, it becomes very shy. It can be kept with urostriatum, but each species should be present in sufficient numbers of its own kind.

It rarely breeds in the aquarium. In successful attempts the eggs have been reported to be laid in a bubble nest built under leaves at the surface. The fry can be raised on freshly hatched brine shrimp and microworms.

• It is hardy; nitrate should be kept low with regular water changes.
• A lack of hiding places causes stress and loss of appetite.
• Its long barbels can wear on sharp decor and rough substrate; prefer soft sand and smooth roots.
• Be careful with salt and copper-based medications.

Sexing is difficult. Viewed from above, mature females look plumper; males are slimmer.