Photo: Per-Ola Norman
The ocean sunfish or common mola (Mola mola) is the heaviest known bony fish in the world. It has an average adult weight between 247 and 1,000 kg (545–2,205 lb). The species is native to tropical and temperate waters around the globe. It resembles a fish head with a tail, and its main body is flattened laterally. Sunfish can be as tall as they are long when their dorsal and ventral fins are extended.
Sunfish live on a diet consisting mainly of jellyfish, but because this diet is nutritionally poor, they consume large amounts to develop and maintain their great bulk. Females of the species can produce more eggs than any other known vertebrate, up to 300,000,000 at a time. Sunfish fry resemble miniature pufferfish, with large pectoral fins, a tail fin, and body spines uncharacteristic of adult sunfish.
Adult sunfish are vulnerable to few natural predators, but sea lions, killer whales, and sharks will consume them. Among humans, sunfish are considered a delicacy in some parts of the world, including Japan, Korea, and Taiwan. In the EU, regulations ban the sale of fish and fishery products derived from the family Molidae. Sunfish are frequently caught in gillnets.
A 2.7mm-long larva of the ocean sunfish, Mola mola, from the Ichthyology Collection of the National Science Museum, Tokyo
A member of the order Tetraodontiformes, which also includes pufferfish, porcupinefish, and filefish, the sunfish shares many traits common to members of this order. The ocean sunfish, Mola mola, is the type species of the genus.
This rare footage of a gigantic sunfish was captured on film by photographer Miguel Pereira off the coast of Portugal. The huge creature dwarfs the divers as it swims past. The slow-moving fish and clear water allow for some spectacular close-ups of this amazing animal.
Skeleton of an ocean sunfish, Mola mola, Naturhistorisches Museum Wien
A sunfish caught in 1910, with an estimated weight of 1600 kg (3500 lb) - P.V. Reyes of Avalon CA
Pyrosomes, genus Pyrosoma, are free-floating colonial tunicates that live usually in the upper layers of the open ocean in warm seas, although some may be found at greater depths. Pyrosomes are cylindrical or cone-shaped colonies made up of hundreds to thousands of individuals, known as zooids. Colonies range in size from less than one centimeter to several metres in length.
The team on this dive are extremely experienced, with over 20,000 dives around the world logged between them, but no-one had ever seen a pyrosome before!
Each zooid is only a few millimetres in size, but is embedded in a common gelatinous tunic that joins all of the individuals. Each zooid opens both to the inside and outside of the "tube", drawing in ocean water from the outside to its internal filtering mesh called the branchial basket, extracting the microscopic plant cells on which it feeds, and then expelling the filtered water to the inside of the cylinder of the colony. The colony is bumpy on the outside, each bump representing a single zooid, but nearly smooth, though perforated with holes for each zooid, on the inside.
Pyrosomes are planktonic, which means their movements are largely controlled by currents, tides, and waves in the oceans. On a smaller scale, however, each colony can move itself slowly by the process of jet propulsion, created by the coordinated beating of cilia in the branchial baskets of all the zooids, which also create feeding currents.
Giant Pirosome. Maldives Islands
Pyrosomes are brightly bioluminescent, flashing a pale blue-green light that can be seen for many tens of metres. The name Pyrosoma comes from the Greek (pyro = "fire", soma = "body"). Pyrosomes are closely related to salps, and are sometimes called "fire salps". Sailors on the ocean are occasionally treated to calm seas containing many pyrosomes, all luminescing on a dark night.