“Catching and releasing trout is usually performed as quickly as possible with minimal playing and handling time. Excessive playing can damage a trout’s throat and gills. Plus, the skin of a trout is covered with a substance that protects it from disease and infections. Our dry hands (and even nets) can wipe this substance from the skin, exposing the trout to harm.” (X)
Rightly so, we are advised to wet our hands before handling a fish, because we might harm the protective coating of the fish with dry, abrasive hands or nets. But, what is that protective coating?
“Fish secrete a mucoprotein protective slime coat that covers the scales and skin. This slime coat acts as a defense against invasion by bacterial, parasitic, and fungal pathogens.” (more here @ Arkansas Stripers)