Really giant clams

The entire genus Tridacna is commonly referred to as giant clams, but most clams we see in the hobby (T.maxima, T.crocea, and T.deresa) are less than 12 inches, if even 4 inches. It's T.gigas that is the real champ of the Tridacnids.

Natural zebrafish outcompete Glofish for mates

Researchers found that wild male zebrafish consistently beat out genetically modified Glofish for potential mates. Females wanted to mate with Glofish males, but wild males prevented it. Evolution is usually thought of in terms of "survival of the fittest, but the study shows that mating success is actually a stronger driving force.