The weird and wonderful sunfish: Everything you need to know!

Recently, our Two Oceans Aquarium team was involved in a huge sunfish rescue in the Transnet Robinson Dry Dock. To many, the sunfish is an almost alien-looking animal – with a weirdly shaped body that seems to be missing another half, it could be from another planet. Naturally, the rescue sparked many questions from our Aquarium family: What is a sunfish? Where do they live? What do they eat?

What is a sunfish?

Sunfish are from the family Molidae, known informally as molas. Swedish naturalist Carl Linnaeus coined the name in the 1700s, noting that when they basked in the sun, they looked like large, grey millstones or "mola" in Latin.

There are five species in the Molidae family: Ocean sunfish (Mola mola), hoodwinker sunfish (Mola tecta), giant sunfish (Mola alexandrini), slender sunfish (Ranzania laevis), and sharptail sunfish (Masturus lanceolatus).

Whether they look like it or not, sunfish are predators! They prey mostly on jellyfish but have also been recorded preying on other siphonophores (animals that travel in colonies, like blue bottles). Sunfish even migrate, following seasonal changes in jellyfish populations over relatively short distances. Furthermore, their large eyes allow them to spot prey over great distances and in darker areas – their visual abilities are much greater than some other ocean predators like catsharks and dolphins.

Unlike most other fish, sunfish do not have a swim bladder, the organ used by fish to adjust their buoyancy. Instead, sunfish have a layer of jelly under their skin that makes them neutrally buoyant, meaning they neither sink nor float in the water! This jelly layer serves another purpose: It tastes absolutely disgusting, which is enough to ensure that they don’t get eaten by humans! Although, this doesn’t perturb some predators such as orcas, great white sharks, and seals.

Where do sunfish live?

Just by looking at a sunfish, we can get a pretty good idea of where they would fit in the ocean – as large animals, they need a lot of space!

Sunfish are exclusively ocean-faring animals, and form part of the epipelagic ecosystem. The ocean is made up of multiple zones – from the surface (pelagic) zone to epipelagic, mesopelagic, bathypelagic, and abyssalpelagic – these all describe deeper and deeper segments of the ocean.

The epipelagic, where sunfish most commonly live, is the upper 200 metres of the ocean, where sunlight still reaches. These ocean-faring fish can easily dive to depths of more than 600 metres into the mesopelagic zone, where waters become darker, pressure increases, and temperatures drop to freezing.

They have a fascinating way of combatting the cold waters after diving. Sunfish spend a lot of time sunbathing by turning on their sides at the ocean surface. This helps to soak up the sun and regulate their body temperature, allowing them to forage in the colder depths. Thus, they only forage and hunt during the day when the sun is out and ready to warm them up!

Sunfish inhabit temperate and tropical seas, so are a common occurrence here in South Africa. The ocean sunfish, southern sunfish, slender sunfish, and sharptail mola have all been identified circumglobally, in all five oceans. The newly discovered hoodwinker sunfish has only been identified in the southern Pacific and Indian oceans, from Chile to South Africa, but it likely has a similar distribution to other species. All five species have been spotted right here in Cape Town.

How do sunfish reproduce?

Sunfish have some interesting breeding habits… When mating, males and females spawn huge amounts of eggs and sperm into the water column – up to 300 million eggs at a time! The sperm and eggs are fertilised in the water column, but of course, the odds are incredibly slim that all the eggs will be fertilised. Even mating seasons are non-existent – sunfish simply take advantage of being near other sunfish.

Sunfish larvae are a minuscule 2mm when hatched! They stay in small schools for protection from predators until they develop into fry. From here, they grow rapidly and leave the school once mature. Adult sunfish brave the ocean on their own, and current estimates state that it takes approximately 20 to 25 years to attain their full size from larvae.

What should I do if I spot a sunfish?

Sunfish are vulnerable to extinction on the International Union for Conservation of Nature (IUCN)’s Red List. The greatest threat to this species is being caught as bycatch – while humans don’t eat sunfish, they are still threatened by commercial fishing vessels. In South Africa alone, over 340 000 sunfish are caught as bycatch every year. Plastic litter, mistaken by sunfish as delicious jellyfish, is another huge threat.

For these reasons, we must protect sunfish! The Two Oceans Aquarium Foundation encourages regular ocean users to record their sightings of all sunfish species to aid in global studies. If you spot a sunfish, simply report your sighting on WhatsApp to 076 092 8573 or email sightings@aquariumfoundation.org.za. Include as much information as possible, but ideally, any photos/videos you take, a GPS location or map pin, the date and time of your sighting, and any behaviours you observed.