by Annette J Beveridge
The oceans are filled with strange creatures and the sunfish is no exception. Using their large dorsal and anal fins to swim, they can move at speed when avoiding predators or, when they locate prey but are mostly seen simply drifting in the ocean currents. They are the heaviest of the bony fish weighing up to 1500 lbs – their size is impressive and they dwarf divers who are fortunate enough to swim with them. At birth, they have a back fin but this disappears as they mature. It appears to fold into the fish itself. Lying on one side as they manoeuvre through the ocean, these are spectacularly odd-shaped fish that have been mistaken for sharks when they emerge from the depths.
Descended from bony ancestors, the sunfish has cartilaginous tissues which is lighter than bone and as an adaptation, enables the fish to grow to an immense size. The teeth are fused – resembling a beak and they are unable to close their mouths. Sunfish have few enemies once they reach maturity but they do fall foul of boats when floating just beneath the surface and are at risk of becoming entangled in drift nets. Immature sunfish are predated on by sharks, whales. or sea lions.
The millstone of the sea
Sunfish are solitary. They will make use of cleaning stations in groups and float at the surface, inviting small fish or birds to pick off the parasites. They have even been known to breach right out of the water landing with a huge splash to dislodge any parasites. The scientific name is mola mola, and it translates as millstone which is an apt name for this fish.
The preferred diet is jellyfish, but they need to consume many so to sustain their growth. Sadly, some sunfish die due to consuming plastic bags which when floating in the sea look so much like their choice prey. Although they are seen floating at the surface, much of the time is spent hunting in the deeper parts of the ocean. The preferred depth is 160-600 feet; however, they can dive down to 2,600 feet.
Eggs and sperm are released at the same time as it ensures a greater number of eggs are fertilised and they spawn several times. The newly hatched fry weigh less than a gram and resemble miniature puffer fish with large pectoral fins, a tail fin and body spines.
It is believed that sunfish thermally recharge during their time at the surface and they do this after diving into the cold depths for feeding. They have also been sighted in areas far outside their typical habitat including southwest England. This may suggest rising marine temperatures or, that the fish are simply drifting in the currents.