Catfish as an animal pertains to fish with barbels resembling whiskers around their mouths, like a wise goatee. Catfishing as an action is to do with presenting a false version of yourself to deceive a person’s view of you. In the case of Clarias batrachus, also known as the Walking Catfish, this species has been playing both parts as an aquatic animal that can not just breathe but also walk on land. I don’t know what to believe anymore.
More impressive even than that is that this species, invasive to Florida, has been strutting about on urban streets after emerging from storm drains. Scientists couldn’t understand how the catfish were orienting themselves in terrestrial environments so efficiently, so they carried out a study, published in the journal Fish Biology, to see what sensory cues the walking catfish were relying on to survive.
They placed individual catfish in what the study terms “terrestrial arenas”, which springs to mind scenes from Gladiator but in reality was something resembling a paddling pool. They exposed the fish to nine treatments: two controls, L‐alanine, quinine, allyl isothiocyanate, sucrose, volatile hydrogen sulfide, pond water, and aluminum foil. To the uninitiated, it sounds a bit random, but by presenting the fish with safe options (such as the pond water) and potentially hazardous options (such as the hydrogen sulfide, a highly corrosive substance), they could detect if the fish were reacting to the treatments or just moving randomly.
Their results showed the fish were drawn towards alanine and pond water but moved away from the hydrogen sulfide. The drive towards or away from certain treatments suggests the fish can detect things in their environment through taste and/or smell, which is known as chemoreception. For the walking catfish, this was possible both through direct contact and through the air, which the researchers state is vital in their ability to navigate terrestrial environments. This is the first time terrestrial chemoreception has been described in a fish species.
As well as testing the fish in their paddling pool arenas, the study interviewed 99 people from Florida wildlife‐related Facebook groups, a state where invasive walking catfish are widespread, focusing on members who had personal observations of C batrachus on land. Their accounts indicated that walking catfish appear to emerge most frequently during or just after heavy summer rains, particularly from stormwater drains in urban areas. Fans of Stephen King might be getting strong IT vibes right about now, but fortunately instead of pulling a Pennywise and feasting on innocent children, it seems the invasive catfish are only after the insects. Phew.
It’s hoped that by better understanding the lives of these unusual catfish scientists can be better armed in managing invasive populations. They might not be threatening our kids with red balloons, but, clown or no clown, a widespread partially terrestrial predator is bad news for the insect populations of Florida.
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