Ocean Sunfish (Mola sp.)

Mola descended from bony ancestors, its skeleton contains largely cartilaginous tissues, which are lighter than bone, allowing it to grow to sizes impractical for other bony fishes.

ANATOMY

Molas are in the order Tetradontiformes (means 4 teeth shape). Common characteristics of fish in this order is a beak or 4 teeth in their mouth and an internal toxin avoid being eaten. Other fish in this order include: Pufferfish, Triggerfish, Porcupinefish and Filefish.

SPECIES

Members of the Mola family are native to tropical and temperate waters worldwide. Molidae family comprises of 3 genera. Within the Mola genra there are also three species:

Mola alexandrini, Mola mola, & Mola tecta. The species seen most often in Nusa Penida area is Mola alexandrini.

LIFE CYCLE

Molas start their lifecycle as a small egg. Female will produce 300 million eggs in a breeding season and the eggs measure 1.3mm. Fertilization of eggs is done externally therefore adult molas must aggregate during mating season. The eggs all hatch together. The newly hatched larvae all swim together for protection from predators. The Larvae grows rapidly, losing it’s tail and developing spines to become a Fry. At 15 mm, the fry begin to look like their cousins, the pufferfish. By 37 mm in length, the body spines are much less prominent, the body is deeper and more compressed, and the beak-like teeth and clavus have developed. The adult Ocean Sunfish has no visible spines.

As juveniles they continue to school in groups for protection, slow swimmers. Upon reaching maturity, due to increased size and improved swimming ability, molas will abandon protection group and become more individuals. Throughout their lifecycle molas will grow more than 60 million times their birth size, arguably the most extreme size growth of any vertebrate animal.

DIET & FEEDING

Adult Molas typically weight 247-1,000 Kgs, and they need to eat 1-3% of it’s body weight daily. Omnivores, eat both animals and plants. Jellyfish & salps consist 15% of their diet. Jellyfish have low nutritional value, therefore Mola’s need to supplement their diet with higher value food sources. The low nutrient content of their prey means that they must eat huge quantities Molas will spend approx. 50% of their day foraging. Diving to depths deeper than 600m to forage for food. Food sources are throughout the water column, from shallows to deep sea floor.

Molas have open mouths with four teeth fused together to form two bony plates, like a beak. They also have spiny pharyngeal teeth in their throat which shreds their food into tiny particles as they suck it back and forth.

CLEANING

As deep water fish, they are prone to infection by parasites. 54 different species of parasite have been identified as living on the skin of molas. One mola parasite is the larval stage of a shark tapeworm so at some point the mola most likely falls prey to shark enabling this parasite to complete its lifecycle!

Molas will use other organisms to clean parasites off their skin. Cleaning can take place both underwater and on the surface. At underwater “cleaning stations” aggregations of different types of cleaner fish will focus on eating particular parasites, cleaning certain body regions. For example at the mola cleaning stations on the reefs around Nusa Penida, cleaning wrasse will focus on inside and around the mouth area of the mola. Bannerfish clean around the head. Butterflyfish clean wounds and around the body of the mola. Emperor Angelfish clean around the tail of the mola.

SURFACE SUN-BATHING

Surface cleaning also takes place, whereby the Mola floats on the surface while the seagull removes the parasite. However molas will float their bodies on the surface for other reasons as well. Molas dive to extremely deep ocean depths. Recorded deep dive 644 meters in the Galapagos, however it is believed they can dive to deeper depths up to 800 meters. The average deep dive for a sunfish lasts less than 10 minutes before they return to shallow waters. Their body temperature drops after deep dives to icy cold waters. Prolonged periods spent in water at temperatures of 12 °C (54 °F) or lower can lead to disorientation and eventual death. Return to shallower waters or surface to warm up. Molas will lay on their sides on the water’s surface soaking up the sun’s rays largest surface area OR stay in shallower warmer waters after less deep dives. This warming period enables the mola to warm up so they can go foraging for food again. Interestingly, sunfish are able to warm their bodies so effectively that scientists suspect there are underlying adaptations we have yet to discover. This is further supported by the fact that large sunfish lose heat slower than small ones.

Support Research & Conservation of Molas

Learn more about Molas as well as other megafauna of Bali such as sharks, mantas, and turtles in our week-long Megafauna courses held several times throughout the year:

Blue Corner Marine Research conducts regular reef health monitoring and collects sightings data for Molas and Manta Rays in the Nusa Penida Marine Park, Bali. We also focus on marine habitat restoration with ongoing coral restoration projects.