scombrids. The fish propel themselves by a lift-based labriform mode of swimming, that is, by flapping their pectoral fins. This, together with their forked caudal fins and depressible median fins, indicates they swim at constantly high speeds like tuna. Lampris guttatus are able to maintain their eyes and brain at 2 °C warmer than their bodies, a phenomenon called cranial endothermy and one they share with sharks in the family Lamnidae, billfishes, and some tunas. This may allow their eyes and brains to continue functioning during deep dives into water below 4 °C. Squid and euphausiids (krill) make up the bulk of the opah diet; small fish are also taken. Pop-up archival transmitting tagging operations have indicated that, aside from humans, large pelagic sharks, such as great white sharks and mako sharks, are primary predators of opah. The tetraphyllidean tapeworm, Pelichnibothrium speciosum, has been found in L. guttatus, which may be an intermediate or paratenic host. The planktonic opah larvae initially resemble those of certain ribbonfishes (Trachipteridae), but are distinguished by the former's lack of dorsal and pelvic fin ornamentation. The slender hatchlings later undergo a marked and rapid transformation from a slender to deep-bodied form; this transformation is complete by 10.6 mm standard length in L. guttatus. Opahs are believed to have a low population resilience. References Lampridae Extant Miocene first appearances