Yellowfin Grouper (Mycteroperca venenosa) The yellowfin derives its scientific moniker, venenosa, from the toxicity of the flesh of some large specimens in areas where ciguatera poisoning occurs when humans eat toxic fish. Also called the rockfish, the yellowfin is variably colored, commonly olive-green with rows of rounded, irregular, dark splotches on its back. Its belly is often salmon pink, and its mouth is yellow inside and along the corners. The outer 1/3 of the pectoral fin is a brilliant yellow. Yellowfin taken from waters deeper than 100 feet are often bright red with even darker red body blotches. Yellowfin may grow to 30 inches and about 20 pounds.