Abstract
The author observed the behavior of a cobia (Rachycentron canadum) associating with a sting ray (Dasyatis maculatus) in a large circulating channel tank of the Oita Ecological Aquarium. The cobia never left the sting ray the whole day, but accompanied it as shown in the photographs from November 1965 until May 1966.
As the sting ray never took food, a fish-keeper often dived in the tank wearing a SCUBA (Aqua lung) to feed the sting ray. Though the diver pushed some food into the mouth or throat of the sting ray, the food was thrown up at once in most, cases. The cobia, swimming around the sting ray, took the thrown-up food more, quickly than the diver picked it up.
After the sting ray was removed from the tank, the cobia associated temporary with a leopard shark (Triakis scyllia), a sting ray (Dasyatis akajei), and a larger cobia, but did not associate with a nurse shark (Orectolobus japonicus), a horned shark (Heterodontus japonicus), and other large fish (Seriola).
The behavior of the cobia suggests the associating behavior of a pilot fish (Naucrates) and that of a shark sucker (Remora) with large sharks. It is interesting that the cobia is quite similar to a shark sucker in form and stripes and to a pilot fish in the separate spinous dorsal fin which can be deressed in its groove.
