As bottom feeders that root around in the muck for smaller creatures to eat, catfish continually are exposed to all sorts of disease-causing microorganisms. But that doesn't seem to hurt them much, which aroused scientists' curiosity. Eventually, they discovered that the slimy mucus catfish secrete onto their skin protects them against the bugs that they encounter in their environment.
In a study published in World Applied Sciences Journal in 2011, Indian researchers collected epidermal mucus from catfish caught in that country's Parangipettai coastal region, and tested it against 10 different types of disease-causing bacteria and 10 different fungi. The researchers found that the mucus was very effective in inhibiting the growth of various microbes dangerous to humans, including E. coli and Klebsiella pneumoniae, which attacks the lungs [source: Anbuchezhian, et al.].