Sunfish: the suitcase with fins

A rarely seen sunfish washed up in Ahuriri/Napier recently. Ranger in Te Matau-a-Māui/Hawke’s Bay Chris Wootton interviews Auckland Museum’s Marianne Nyegaard about this intriguing ‘suitcase with fins’.

By Chris Wootton

Sunfish aren’t your ordinary visitor to Te Matau-a-Māui/Hawke’s Bay. When a washed-up sunfish on Ahuriri/Napier beach was reported to 0800 DOCHOT, we set about finding out who (if anyone) had an interest in these bizarre sea creatures.

Our investigations led to Marianne Nyegaard who specialises in sunfish as a research fellow at Auckland Museum. She also runs the New Zealand-based Ocean Sunfish Research Trust, which promotes sunfish citizen science.

I called Marianne to find out about sunfish and the significance of this find.

Ranger Chris: What’s special about sunfish?

Marianne: I’m so pleased this sunfish was reported in. Even though these fish are huge and hard to ignore, we don’t know a lot about them.

The sunfish found in Napier is a little-known species only discovered in 2017. There are five species of ocean sunfish worldwide. Four of the species grow to a huge size, and while all are found in New Zealand, only two of these are common here.

Ranger Chris: Can you describe where they sit in the fish world?

Marianne: Ocean sunfish are most closely related to pufferfish and porcupine fish. If you imagine a hugely enlarged and flattened pufferfish with the tail cut off, you pretty much end up with a sunfish.

The Latin name for sunfish is Molidae (family name) or Mola (genus name), meaning millstone – in reference to the resemblance.

The species most common here in New Zealand are giant sunfish mola alexandrini, which can reach 2.3 ton in body weight and the Hoodwinker sunfish Mola tecta, which was only discovered in 2017.

Ranger Chris: How many turn up around our coasts?

Marianne: Not many, but we do get a handful of sunfish strandings across New Zealand in a year. The last reported stranding was in Ruakākā, near Whangārei, back in July. However, sunfish are fairly commonly seen further from our coast, for example by marlin fishers and commercial longliners.

They are an epipelagic species, meaning they hang out within 200 m of the ocean’s surface, however, they can dive to at least 1000 m. They dive to forage and spend time in shallower waters to warm up between foraging trips.

It’s hard to determine exactly why this sunfish beached. Sunfish may get disoriented and lost in unfamiliar marine territory such as shallow water. But we don’t know for certain.

Ranger Chris: They’re certainly odd-looking creatures – basically a massive, flattened orb with a couple of huge fins and a parrot-like mouth. Why did they evolve like this?

Marianne: Their large size possibly evolved to enable them to dive into deep, cold waters for food. Being large gives them thermal advantages in colder water.

To allow them to yo-yo between feeding and warming up, they have lost their swim bladder over evolutionary time.

This means they have no buoyancy aid.

To accommodate their huge mass, sunfish skeletons are massively reduced and soft, like a shark’s cartilage.

Presumably to make up for the soft skeleton, sunfish have evolved extremely thick skin (several centimetres). I’d describe them like a massive suitcase with fins. They are almost inflexible apart from the flap (clavus) on their back, used for steering. This flap is unique to the ocean sunfishes and isn’t a real tail.

Despite their clumsy looks, sunfish are terrific swimmers.

Ranger Chris: Do they have any enemies?

Marianne: Orcas, sealions and sharks prey on them. I’ve seen sunfish with chunks taken out by these predators. Most commercial fishers don’t bother with sunfish.

Ranger Chris: Is there anywhere in the world where they are consumed by people?

Marianne: They are consumed in parts of Asia. In Taiwan there are diverse ways of preparing sunfish, including your usual stir fry, soups and dried skin in salads.

There’s also a dish of mixed swallow’s saliva and sunfish, which can be consumed with sunfish collagen tea.

A Japanese cookbook dating back to1636 describes sunfish.

Sunfish were traditionally eaten in the Mediterranean, but the European Union now bans their consumption due to concerns about toxin levels in these species.

Ranger Chris: What do sunfish eat?

Marianne: They prey on gelatinous sea creatures such as jelly fish and salps. They are well adapted to this with their parrot beak-like mouth. They have an internal set of teeth in their throat, much the same as the monster in the movie Alien!

Ranger Chris: Lovely. I’d need a set of internal throat teeth if I ate jellyfish all the time too. What are salps?

Marianne: They’re a type of tunicate and can either be solitary or in colonies. I’d describe them as little floating bags that sieve the ocean for tiny plankton.

Ranger Chris: This Napier specimen was big at 1.7 m long and 1.9 m from fin tip to fin tip. What are young sunfish like?

Marianne: Sunfish hatch at around 2 mm and go through a crazy stage of metamorphosis where they lose their tail, have spines and strange shapes, and look like little Pokémons. Very little is known about this stage of sunfish life.

Juvenile sunfish – some tens of centimeters long – are tiny compared with the adults, and school together presumably for safety, but they grow quickly.

As adults, they don’t school and aren’t found in congregations. They become solitary or semi-solitary and are epic at social distancing!

Ranger Chris: What should people do if they find a sunfish washed up on their beach?

Marianne: Call 0800 DOCHOT and get directed through to me at the Auckland Museum.

You can also email me directly, or message me on Facebook or Instagram (Ocean.sunfish.research).

When COVID lockdown levels allow, we try to conduct necropsies on stranded specimens. They’re normally too big for a freezer so we need to travel to them.

When that’s travelling to the fish isn’t possible, we are constantly amazed at how willingly people help. It’s pretty straight forward – photos, a couple of measurements and a small sample for genetics, with assistance from us of course!

Ranger Chris: I’m pleased we could help your research on this unusual sea creature. Kia ora raa!

Marianne: This find is like gold for research and building understanding of sunfish. People can visit Ocean Sunfish Research’s website for more information.