Last November (2019), The CWHC was informed that a very unusual fish had washed up on the red shores of Prince Edward Island. The Mola mola (or “Ocean Sunfish” as it is better known) typically prefers temperate and tropical waters farther south, and so it was a surprise to find one on our shores during the late fall when the water is anything but warm. These fish typically follow the warm oceanic currents and it is possible that it became entrapped in the Northumberland Strait when it was trying to make its way south again as the water became colder.
We had never performed a necropsy on a sunfish at the Atlantic Veterinary College before; even getting it in through the bay doors was a challenge both due to its extremely awkward shape (which has been likened to many different things, including an upside down car, a dinner plate, and a millstone) and its massive size which weighed 422 kg (although some specimens weigh up to several tonnes). This fish is unique both inside and out. Its outer epidermis is extremely rough (similar to a sharks skin), and its body wall is composed predominantly of a firm cartilaginous substance which even coated its gills. A few bones scattered throughout the fins make this species the largest boney fish on the planet.
When we get unusual species like this into the college it always attracts a large crowd of students who are keen to learn first-hand about their biology and diseases.
Testing is ongoing for this sunfish, and during its necropsy we identified a number of interesting parasites in its gills, liver, and gastrointestinal tract. Most of these parasites are likely normal commensal organisms and we have submitted them for parasite identification. It seems more than likely at this point that this fish was “cold-stunned” due to the rapidly dropping water temperature which caused it to die and subsequently strand on the beach. As our climate warms, it is more than likely that we will increasingly find unusual species, both large and small, appearing in our beautiful Gulf.
Special thanks to the PEI Department of Justice & Public Safety (Investigation & Enforcement Division) for their collaborative efforts to retrieve and submit this specimen to the CWHC.
Submitted by:
Laura Bourque – CWHC Atlantic wildlife pathologist
The day I found it I was amazed. That’s my shovel in the background.