Sometime in the late 1950s, an aquarium fish farm in southeast Florida — apparently dissatisfied with just selling exotic fare to enthusiasts around the U.S. — decided to deliberately introduce a small South American fish into the canals of suburban Miami.
What once swam quietly in fish tanks, navigating miniature sunken treasure chests and tiny deep-sea divers alongside those adorable neon tetras and the surly betta that just hung out in the upper corner, scowling at its neighbors, the oscar suddenly swam freely in the near-tropical freshwater canal system on the eastern edge of the Everglades.
Today, it might be the most abundant invasive fish in what has become perhaps the most manipulated plumbing system for both urban and agricultural support in the United States. The oscar (Astronotus ocellatus) is native to Amazonia, and swims abundantly in its home rivers, like the Amazon, the Oronoco and the Rio Negro. But, according to a 2018 revised report from the U.S. Fish and Wildlife Service, the oscar in its various hybridized forms makes up a big portion of the recreational fishery in south Florida. Not only is it established in the Everglades, but its largest representatives come from Lake Okeechobee and points farther north.
According to the report, the oscar remains beloved by aquarium enthusiasts, but it’s also a serious piscavore that grows quickly. When a little kid wakes up in the morning to feed the fish only to find that the guppies have mysteriously disappeared, it doesn’t take much deductive reasoning to know that the only fish still in the tank likely ate them.
“Oscars are very common in the aquarium trade. Because they grow large in aquaria and are piscivorous, individuals are likely to be released into natural waters by aquarists loath to kill their pets,” the report reads. “This likely accounts for the numerous instances of single specimen records from both temperate and subtropical states.”
Indeed, the oscar is also established in Hawaii and in the U.S. territory of Puerto Rico, where it was introduced both intentionally to provide recreational fishing opportunities, and by those who didn’t like the fact that it wasn’t happy simply gulping fish-food flakes.
Of course, the Everglades canal system — particularly on the east side of the complex where fresh water dominates — is home to dozens of invasive fish species from tropical climes the world over. The oscar is joined by predatory snakeheads, prized peacock bass, various other cichlids and tilapia subspecies, walking catfish, knife fish, surgeon fish and even freshwater jellyfish.
The oscar, like the peacock bass, seems to be a preferred non-native, and there were efforts to stock it in other states — even states like Wisconsin and Alaska. These efforts were generally unsuccessful, even in warm-weather states like Texas, Louisiana and Mississippi. In its native range, it’s prized for its table fare, and anglers in south Florida don’t seem shy about harvesting these fish, either.
The oscar’s kryptonite, it seems, is cold weather and cold water. In the Everglades, after a prolonged period of warm weather, the South American fish becomes even more numerous — it does well when there are no freezes or bouts with cold that, while uncommon, occasionally do happen. When a wintry blast settles over the Everglades, oscars are generally among the early casualties, which isn’t surprising considering its tropical origins.
I caught my first oscar in the canals and froggy waters along the Tamiami Trail recently — a palm-sized black oscar that hit a Clouser and put up an impressive battle for a fish that was otherwise average. It swam in the same water as native bream and long-nose gar, both of which also hit the same Clouser pattern (the gar, thanks to its toothy snout, didn’t stay hooked). Judging by the fight, I could see why the canals were lined with anglers the closer we got to the outskirts of Miami.
Farther west, as the glades get a larger influx of salty water from the Gulf of Mexico and Florida Bay, the canals host fewer of the South American invaders and become a fishery that’s more tuned in to traditional fare, like snook, speckled trout, redfish and baby tarpon.
And, not surprisingly, there are fewer roadside anglers (the trail is a solid on-foot foot fishery, even with the occasional encounters people have with alligators that are conditioned to seeing and not fleeing from humans) on the “salty side” of the Everglades that’s accessible by foot and vehicle.
If it’s done anything good for the Everglades — and that’s absolutely debatable — the oscar has given anglers in a largely urban area a source of both recreation and food. It’s a burrower and an ambush predator, so it’s certainly had an impact on the freshwater system of the Everglades. In fact, its presence in the canals (along with presence of tilapia) is the reason fisheries officials in Florida introduced peacock bass — the oscars were doing too well before the 1980s introduction of peacocks. In South America, the oscar is a prime source of food for the more coveted peacocks. In the Everglades canals, in a system that barely resembles its native state, the South American invaders have reprised their roles of predator and prey that originated in Amazonia.
From the pessimist’s perspective, there’s no saving the Everglades where native fish are concerned. It’s just not doable, both from an economic perspective and from a practical viewpoint. From an optimist’s standpoint, the canals on the eastern edge of the glades are just fine like they are, oscars, peacocks, snakeheads, et al. It does, indeed, function, albeit from a human-induced baseline. Fish still eat other fish. Predatory birds still eat fish. Alligators still eat fish. And, perhaps most noticeably, people still chase the fish (maybe more now than ever).
There’s hope for the hydrological function of the Everglades as efforts are ramping up to increase the freshwater flow through the River of Grass to Florida Bay. And that may be where conservationists need to hang their hats.
But the oscar is part of a system today that serves a purpose of its own. For many of the non-purists out there, what matters most is that it serves a purpose beneficial to people by providing a recreational fishing outlet and, in some cases, a source of readily available food. It also provides a dependable prey base for trophy largemouth bass (native fish, by the way) and the ever-popular peacock bass fishery that extends from the Tamiami canals well into the urban Miami area.
The challenge for conservationists? Define “function” and the work to achieve. It very likely has nothing to do with oscars and other introduced fish that do, indeed, function together. Accepting that a contrived fishery made up of introduced fish from the world over is a simple reality while working to heal the Everglades and Florida Bay by increasing water flow and water quality is probably the best possible outcome.
And maybe put oscars on the menu more often.