The yellow "meat" near the top is a strip of fat. you should never eat any fat from a catfish as that is the highest percentage of retained toxins from the water they live in. Many state game agencies now have a pamphlet on this topic. Always trim the yellow fat from all fish species to greatly reduce your consumption of water borne toxins.
The yellow meat on the upper portion of channel cat fillets is not fat, but are accumulations of compounds called xanthophylls. These are the same compounds that cause Yukon gold potatoes to be yellow. Farm-raised channel cats that are fed feed with a high proportion of corn often develop this condition and it is considered undesirable.
Wild channel catfish prey heavily upon insects, and as fry they consume large amounts of phytoplankton. Both insects and phytoplankton accumulate large quantities of xanthophylls which are common in many plants, and are hence accumulated in channel cats. Xanthophylls are poorly metabolised in catfish and they accumulate in hydrophobic (i.e. fatty) portions of the muscle, which are more prevalent on the dorsal side of most fish. They also have an affinity for less dense muscle fiber. Blues have denser muscle and consume less insects and plant matter (primarily shad feeders) than channels and this is why you seldom see this condition in blues; although, I have seen it occasionally on small blues and blue X channel hybrids. Oddly the yellow-meat condition is often less in channels caught from fast-moving water.
These xanthophyllic compounds are not toxic and actually provide health benefits to the consumer; however, since they accumulate in the fatty portions where poly-chloro-biphenyls (PCB's--potential mutagens) toxins also accumulate, they should probably be trimmed off. I don't much care for channels and have eaten this yellow meat on occasions in my younger days. Sometimes it had an "off" flavor and sometimes it didn't. But now if I dress channel cats, I always trim it off.