Hoplias aimara
A large freshwater predator from South America known for its size and mercury accumulation.
Hoplias aimara is a big river fish native to northern South America. It reaches over a metre long and serves as a key indicator for mercury pollution in local waters.
- Largest Hoplias species reaching 120 cm and 40 kg
- Serves as a bioindicator for mercury contamination
- Spawns December to March during rainy season
- Ambush predator active at dusk and night
- Flesh quality leads to severe population depletion
What it is
This species stands out as the largest member of its genus. Adults reach lengths of 120 cm and weigh up to 40 kg. Their bodies are elongated and cylindrical. Colours range from pale brownish gold to solid black, usually marked with dark vertical stripes or patches. Small spots often appear on the head and upper body. The pattern varies by location. Despite their size, they are not typically aggressive towards humans, though rare attacks on swimmers have been recorded without fatal results.
Where it lives
The fish inhabits rivers across northern South America. Its range includes Brazil, Colombia, Venezuela, Guyana, French Guiana, Suriname, and the island of Trinidad. It prefers main rivers and creeks, frequently found in counter current zones. These areas provide suitable hunting grounds. The species thrives in these freshwater environments throughout its extensive geographic distribution.
How it lives
H. aimara acts primarily as an ambush predator. It hunts other fish and eats terrestrial invertebrates that fall into the water. Activity peaks at dusk and night. Attacks on larger vertebrates remain unproven. The fish relies on stealth rather than speed to catch prey. This behaviour suits its habitat in flowing rivers where currents help position it for strikes.
Breeding and life cycle
Reproduction occurs at the start of the rainy season, from December to March. Females produce between 6,000 and 60,000 eggs depending on their size. The timing aligns with environmental conditions favourable for offspring survival. Spawning events are tied directly to seasonal rainfall patterns in the Amazon basin.
Fish and people
Local communities harvest this fish for food due to its quality flesh. Heavy fishing pressure has severely depleted populations in settled areas. The species also serves scientific purposes. High mercury levels in Amazonian populations make it a valuable bioindicator for tracking contamination. Researchers use it to monitor environmental health in river systems.
Status and threats
Populations in settled regions face depletion from commercial and subsistence fishing. Mercury contamination poses another threat, particularly in Amazonia. The fish accumulates toxins, reflecting water quality issues. Conservation status remains unclear globally. Local declines highlight the need for sustainable management practices in heavily fished areas.
Questions people ask about Hoplias aimara
How big does Hoplias aimara get?
Specimens reach 120 cm in length and weigh up to 40 kg. The largest rod and reel record stands at 101 cm. This makes it the largest species within its genus.
Why is this fish important for science?
It accumulates high mercury levels in Amazonian waters. Scientists use it as a bioindicator to track pollution. This helps assess environmental health in river ecosystems.
What does Hoplias aimara eat?
It is an ambush predator feeding mainly on fish. It also eats terrestrial invertebrates falling into the water. Hunting occurs mostly at dusk and night.
Is Hoplias aimara dangerous to humans?
Attacks on divers and swimmers are rare and rarely fatal. The fish is generally docile. Unproven reports suggest occasional aggression but no serious harm.
Good reading and sources
- Hoplias aimara on WikipediaEncyclopedia
- More photos on Wikimedia CommonsPhotos
- Wikidata recordOpen data
The facts on this page come from the Wikipedia article "Hoplias aimara", written by its contributors and used under the CC BY-SA 4.0 licence, and from its Wikidata record (CC0). EveryFish rewrote the text in its own words, with AI assistance, and compares every page with the article to make sure no passage is copied. It may be reused under the same CC BY-SA 4.0 licence with a link back.
It may contain mistakes, and figures change over time. Nothing here is investment or buying advice. If something is wrong, tell us. Last refreshed 2026-11-15.
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