Aquarium veterinarian Dr. Mike Murray and the husbandry team made the decision this morning after a week during which the fish stopped eating and was increasingly unable to swim in the million-gallon Outer Bay exhibit where it was housed.

The sunfish, known by its scientific name Mola mola (“millstone” in Latin), was collected in Monterey Bay in September 2005and placed on exhibit two months later. It grew from an initial size of 22 inches and less than 20 pounds to a length of 6-feet, 7-inches and a weight of 1,247 pounds.

A necropsy is pending.

Another large ocean sunfish was tagged and returned to the wild on January 23. That fish weighed 638 pounds and was 5-feet, 8 inches in length. It was brought to the aquarium in November 2006, just 31 inches long and weighing 56 pounds.

Its 30-day electronic tag will report back on the mola’s travels before the end of February. The data will contribute to the limited but growing research about Mola mola in Monterey Bay.

Monterey Bay Aquarium is the only aquarium in North America to exhibit sunfish. One small sunfish is currently in the Outer Bay exhibit. It will ultimately be tagged and returned to the wild.

As part of its exhibit and research program, the aquarium will be tagging sunfish in the field to learn more about where they travel after they leave Monterey Bay.

The ocean sunfish is the world’s heaviest bony fish. The largest individual on record was 10 feet long and weighted 4,927 pounds. All three species of sunfish are found in tropical and temperate oceans worldwide. Little is known about their life history.

Their disc-shaped bodies appear to be mostly head, with a tail that’s narrow and ineffective for propulsion. To swim, they flap elongated dorsal and anal fins from side to side, using the tail as a rudder. They feed on jellies and other slow-drifting prey.

Sunfish have the shortest spinal cord of any fish, less than one inch long and shorter than its brain. They may have the highest reproductive rate of any vertebrate. A four-foot female contains approximately 300 million eggs. Starting life as larva one-tenth of an inch long, sunfish can increase their weight 60 million times. -- www.mbayaq.org