Opah the Warm Blooded Fish

Fishing Vessel Outer Limits out of Mission Bay, San Diego

The first warm blooded fish!


Earlier this month is was discovered that the opah is warm blooded. The opah or (Lampris guttatus) or moon fish a large, mid-water pelagic fish that is about the size of a man hole cover. While they are not targeted, these fish are taken incidentally in both local recreational fisheries for tuna and the California drift gillnet fishery targeting swordfish. In recent years there has been an upsurge in opah catch and has become increasingly popular in seafood markets. SouthwestFisheries Science Center began collecting biological samples from opah in 2009 and initiated an electronic tagging program in 2011.  The opah, also known as the moonfish, has relatively small red fins decorating its large, round body. These fins, which flap rapidly as the fish swims, turn out to be important in generating body heat for the opah.

Researchers first suspected that something might be strange about the opah after analyzing a sample of the fish’s gill tissue. According to the study, the blood vessels in the tissue are set up so that the vessels carrying cool, oxygenated blood from the gills to the body are in contact with the vessels carrying warm, deoxygenated blood from the body to the gills. As a result, the outgoing blood warms up the incoming blood, a process called counter-current heat exchange. This is a cool innovation by these animals that gives them a competitive edge.

To confirm that these special gills helped the opah stay warmer than the surrounding water, the researchers tagged a number of moonfish with temperature monitors and tracked them. The fish spend most of their time at least 150 feet below the ocean surface. No matter how deep they dive their body temperature stays about 9 degrees warmer than the surrounding water. Fat deposits around the gills and muscles help insulate the fish.

Most other deep diving fish such as tuna and sharks can shunt blood to body parts to keep warm during deep dives but they must surface frequently to prevent their organs from shutting down. Think hypothermia for fish. Warm blood gives opah an edge as their muscles and nervous system likely function faster than cold blooded fish. Which translates into the opah can stay at deep depths for longer periods of time with faster response times and better sight a definite   advantage when hunting cold blooded slow moving prey.

Have a fishing Question drop me a line outerlimitscharters@gmail.com

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