Longhead hemiodus

Argonectes longiceps

Also known as Torpedo hemiodus, False hemiodus

FreshwaterFish

Care at a glance

Temperature: 75–84°F (24–29°C)
pH: 5.5–7.0
Adult size: 11.8 in (30 cm)
Minimum tank: 159 gal (600 L)
Temperament: Peaceful
Social behavior: Schooling
Swim level: Middle
Difficulty: Difficult
Breeding: No record
Rarity: Rare
Origin: Orinoco and Negro basins
Family: Hemiodontidae

Overview

The longhead hemiodus is a large, nervous, fast-swimming schooler that needs both numbers and room. Keep it in a group of six or more, because lone fish and small groups panic and crash into the glass. It cruises the open middle water, so it wants a long tank with clear swimming lanes and steady flow, kept alongside other large but peaceful fish such as silver dollars or big characins rather than anything small enough to be treated as food. Feed sinking and frozen foods with some vegetable matter. A settled group needs a big tank of around 600 liters or more.

In the wild

The longhead hemiodus swims in large, often blackwater channels of the Orinoco and Negro basins, favoring swift, open, sandy stretches. In a tank it needs length above all, with strong water movement, high oxygen, and a sandy floor. Keep the water soft and warm, from about 24 to 29 C, with a pH between 5.5 and 7.0. Bright open water and current matter far more than decor.

Good to know

Argonectes longiceps is a hemiodontid that reaches about 30 centimeters, a slender silver fish built for open-river cruising. Its name means long head, describing the drawn-out snout. Unlike its close relatives in the genus Hemiodus, which rest and swim in a head-up, oblique posture, Argonectes holds a level, horizontal position. Aquarium breeding is unrecorded.

Did you know

Many hemiodus relatives hang in the water at a distinct head-up tilt, but the longhead breaks the family habit and swims dead level, which is one of the quickest ways to tell it apart from its cousins.