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Science Sector

By Cora Berchem, Director of Multimedia and Manatee Research Associate

Armored catfish (Pterygoplichthys disjunctivus)—referred to as plecos—are a common addition to household aquariums, helping to clean the algae off the glass. People usually get them when they are very little, but once they grow too big, they get rid of them by releasing them into the wild. This is how they have become introduced into rivers and waterways in Florida and have become a big problem. They are exotic and invasive—exotic, meaning they are not from Florida, and invasive, meaning they have characteristics that make them very good at taking over their new habitat. Plecos grow very fast, about 3.9 inches (10 cm) per year, and live to be about five years old. They reproduce extremely quickly: one female may lay 30,000 eggs every summer. The males will dig burrows into banks of rivers or springs and guard the nests, so almost all those eggs will hatch, giving them a big advantage over most native fish in Florida.

Now what effect do these catfish have on manatees? Some people see manatees covered in catfish and think the manatee is getting a “spa treatment,” similar to how some cleaner fish on reefs will assist other species by taking off dead skin particles or parasites. Others think the catfish hurt the manatees. Neither is actually the case, but the catfish do “annoy” the manatees by latching on to their skin with their soft, bristly mouths and causing a tickling sensation that will result in the manatee moving to shake off the fish. It’s somewhat comparable to mosquitoes—they don’t really hurt us, but they cause annoyance, especially if we are trying to rest or sleep. Especially during the winter months, manatees may expend extra energy trying to evade the persistent fish when they should be resting. In the winter, it is critical for manatees to rest and conserve energy while at a warm-water site, such as the Blue Spring run. Disruption by catfish can result in manatees being more active and having to go out into the cold river more often to feed to replenish their energy.

Is there anything we can do? While it is impossible to eradicate the catfish, efforts are underway to remove them from certain areas under specific permits. Unfortunately, even removing hundreds from an area such as Blue Spring State Park does not fix the problem, as there are billions more in the adjacent St. Johns River. Fish biologist Dr. Melissa Gibbs from Stetson University even observed the catfish leaving during the day when fishing is going on and returning at night.

We should all keep in mind that releasing any non-native species into the wild should never be done, as it can become a serious problem for native species, like manatees.