ROCKPORT — Photographer Peter Ralston was headed back into Rockport Harbor Aug. 23 on his powerboat, Raven, when he spotted a fin and then the white underbelly of a large fish, “five feet from stem to stern,” he reported.

It was the ocean Sunfish, otherwise known as Mola mola, a weird and mysterious fish, according to Nature Conservancy writer Justine E. Hausheer, on the website Cool Green Science.

They are massive, vulnerable and their “upper and lower teeth are fused into a parrot-like beak that’s stuck permanently open,” writes Hausheer.

Mola mola is of the genus Mola, along with two other species, and Ralston’s friend, Philip Conkling, quotes Henry Bigelow, “the great oceanographer and icthiologist (fish guy) of the Gulf of Maine,” as he wrote: "When these unlucky vagrants are sighted in our cool northern waters, they have usually been chilled into partial insensibility. They float awash on the surface, feebly fanning one or the other fin, the personification of helplessness."

Ralston has encountered sunfish before, and warns boaters, “They are easily hit by inobservant boaters and it was reported that two have been seen very locally.”

He said this particular sunfish was midway in Rockport’s outer harbor.