In addition to its importance as a way for finding food, the sense of smell is also important in social behavior. Experiments have shown that yellow bullheads are able to distinguish one individual of their species from another based on smell alone.
Once they attain a fairly large size, yellow bullheads have fewer predators, but bullhead eggs and fry are easy pickings for a wide variety of aquatic predators, including sunfish and even minnows, which hover about the nest, waiting for them to be unguarded for a moment. This explains the parent bullheads’ diligent nest-guarding behavior.
In general, predators of bullheads include any fish large enough to consume them, plus watersnakes, snapping turtles, herons, and raccoons.
As a defense against predation, bullheads (like many other catfish), when attacked, typically stretch out and lock their dorsal and pectoral spines, which makes them much harder to swallow.
Worldwide there are more than 35 families of catfishes in the catfish order (Siluriformes). Most of us could easily identify most of them as “catfishes” by their whisker-like barbels, smooth bodies lacking scales, general nocturnal disposition, and typical bottom-feeding habits. But aquarists know that several tropical cats have bony plates (which still aren’t technically scales) — think “cory cats” (Corydoras spp.) and “plecos” (Hypostomus plecostomus). Aquarists may also be familiar with catfish that are not bottom feeders — think of the “glass catfish” (Kryptopterus) that swim in the middle level of an aquarium. Some other tropical freshwater catfish popular in the aquarium trade aren’t called catfish: one example is the “iridescent green shark” (Pangasius spp.), which you may also find frozen in groceries labeled as “swai,” “panga,” “basa,” or “bocourti.”