Lutjanus campechanus is a specific Gulf and southeastern Atlantic species with a restricted supply and a high price. The name red snapper carries that premium, and DNA barcoding studies of samples bought from restaurants and shops have repeatedly found high substitution rates under it, with other snappers, tilapia, rockfish and unrelated species turning up in place of the named fish.
Substitution rates for this particular name have come out at the high end in almost every survey that has looked, including work by conservation organisations and by government laboratories, in both the United States and elsewhere. It is one of the standard examples used when seafood fraud is discussed.
The mislabelling is not only an economic problem. It confounds the traceability that fisheries management depends on, it can put fish from poorly managed stocks onto plates under the badge of a well-managed one, and it can conceal species that carry specific health advisories. What is harder to pin down is where in the chain the substitution happens, since surveys typically sample at the point of sale and cannot see upstream.