Armored catfish cause serious ecological damage wherever they establish populations outside their native South America. They erode shorelines, outcompete native fish, harass endangered manatees, and reproduce so prolifically that controlling them is extremely difficult. Seven species or hybrids have now been reported across five continents and 21 countries, making them one of the most widespread freshwater invasive fish in the world.
Where They Come From and How They Spread
Armored catfish belong to a group of suckermouth species native to the Amazon, Orinoco, and Paraná river basins in South America. The two most commonly found outside their native range are the vermiculated sailfin catfish and the Amazon sailfin catfish. Both are popular aquarium fish, sold under names like “pleco” or “plecostomus,” and most invasive populations trace back to aquarium releases or escapes from fish farms.
Once released, these fish thrive. They tolerate low-oxygen water that would stress or kill many native species, and they can survive brief periods out of water by gulping air. Florida, Texas, Hawaii, Mexico, and much of Southeast Asia all have established breeding populations. Warm-water systems like springs, canals, and slow rivers are particularly vulnerable.
They Dig Burrows That Destroy Shorelines
One of the most distinctive problems armored catfish create is physical. Males excavate nesting burrows into riverbanks and canal walls, and these burrows are not small. Researchers studying populations in Florida measured tunnels ranging from about 8 inches to over 4 feet long, with an average length of roughly 2.5 feet. A single burrow can displace nearly 13,000 cubic centimeters of sediment, roughly the volume of a large bucket.
The damage scales up quickly because these fish nest in colonies. A typical colony of 12 burrows removes about 0.15 cubic meters of soil from a bank. Across surveyed sites, burrowing activity removed an estimated 1 to 4 percent of the bank volume in a one-meter-deep section. Over time, this weakens shorelines, accelerates erosion, and can undermine levees, retention walls, and other flood-control infrastructure. In areas where water management depends on intact canal banks, that erosion creates real engineering problems.
Competition With Native Fish
Armored catfish are algae grazers, scraping food off rocks, submerged wood, and other surfaces with rows of comb-like teeth. In their native rivers, this niche is shared among many species that evolved alongside them. In invaded waterways, they dominate this food source and crowd out native fish that depend on the same algae and organic material.
They also compete for physical space. Their burrows occupy habitat along banks and root systems that native fish, crayfish, and other organisms use for shelter and nesting. The U.S. Fish and Wildlife Service classifies the vermiculated sailfin catfish as high ecological risk, citing competition with native species for food, increased siltation from burrowing, and disruption of endangered species. The sheer density these catfish can reach, sometimes numbering in the thousands in a short stretch of waterway, magnifies every one of these effects.
They Harass Endangered Manatees
One of the stranger consequences of armored catfish invasion involves Florida manatees. At Volusia Blue Spring, researchers documented catfish attaching to manatees with their sucker-shaped mouths to graze algae growing on manatee skin. The catfish use their comb-like teeth to scrape the surface, leaving visible cleared trails on the manatees’ bodies.
This is not a harmless interaction. Underwater video analysis showed that manatees with catfish attached were significantly more active and agitated than undisturbed manatees. They performed barrel rolls, tail flips, and other high-energy movements to dislodge the fish, and they vocalized more frequently, possibly signaling distress. On average, each manatee was surrounded by nearly five catfish at a time, with about 1.6 attached at any given moment. Individual catfish stayed latched on for an average of only 16 seconds before being shaken off, but they often reattached immediately. In roughly 70 percent of observed interactions, manatees changed their behavior after a catfish latched on.
For an endangered species that relies on warm springs for winter refuge, this constant harassment forces manatees to burn energy they need for thermoregulation and survival during cold months.
They’re Built to Survive and Hard to Remove
What makes armored catfish so difficult to control is a combination of physical toughness and reproductive output. Their bodies are covered in bony plates rather than typical fish scales, forming a rigid armor that protects them from most predators. They also have locking spines on their pectoral fins that can injure predators (and fishermen) and make them nearly impossible for birds or larger fish to swallow.
Few native predators in invaded ecosystems can eat an adult armored catfish. Alligators occasionally take them, but the armor and spines make them a poor food choice compared to softer prey. This means population growth is largely unchecked by natural predation once fish reach adult size.
Reproduction compounds the problem. A single female can produce anywhere from about 1,300 to nearly 19,000 eggs per brood, depending on her size. Spawning appears to be continuous rather than limited to a single season, with peaks during periods of high water. Males guard the eggs inside their burrows, giving offspring a high survival rate compared to fish that scatter eggs in open water. The combination of high fecundity, parental care, and few predators means populations can explode within just a few years of introduction.
Damage to Fishing and Local Economies
Armored catfish also create practical headaches for fishermen. They frequently get tangled in gill nets and cast nets, damaging fishing gear with their bony plates and locking spines. In regions where subsistence or commercial fishing supports local livelihoods, large armored catfish populations can make nets unusable and reduce catches of target species. The fish themselves have little commercial value in most invaded regions, so the tradeoff is all cost and no benefit.
Because armored catfish tolerate degraded water conditions better than most native fish, they often become the dominant species in waterways already stressed by pollution or habitat loss. This creates a feedback loop: as water quality declines, native fish struggle while armored catfish hold steady or increase, further shifting the ecosystem away from its original balance.