How big is a sunfish?

Sunfish are the heaviest bony fish species alive today. Find out how large different species grow and how to weigh one. 

How big is a sunfish?

Sunfish are the heaviest bony fish species alive today. Common sunfish weigh around one metric tonne on average, but the biggest common sunfish ever caught weighed over two metric tonnes!

Scientist and camera crew look over a large sunfish on a table

Caption

Scientists carrying out research on a 243kg sharptail sunfish, 2013. Te Papa

What’s the biggest sunfish ever recorded?

The heaviest reliably weighed sunfish was caught off Japan in 1996 – it was 2.3 tonnes, and 2.7m long.

Species of sunfish

Sunfish vary in size depending on species. The little oblong sunfish only grows to about 1m long and about 6kg. The other four species are massive and can be over 3m long – their maximum weights have always been estimated.

They include:

  • Sharptail sunfish –Masturus lanceolatus
  • Ocean sunfish – Mola mola
  • Short sunfish – Mola ramsayi
  • Hidden sunfishMola

Oblong specimen

Caption

Oblong sunfishRanzania laevis (Pennant, 1776), collected Apr 1998, Southern Mahia Peninsula, New Zealand. CC BY-NC-ND licence. Te Papa (P.034929)

How do you weigh a sunfish?

Sunfish, because of their size, are very hard to weigh accurately.

There are huge issues with getting a crane to lift the fish, and scales that could cope. They are also a very awkward shape, which only compounds the problem.

Watch the video below to see how we weigh the sunfish at Te Papa:

How do we store the sunfish?

Nearly every sunfish specimen is preserved as a ‘wet’ specimen, which means fixed in formalin and stored in alcohol in drums and tanks.

Watch the video below to hear from our fish expert, Andrew Stewart, on why we preserve whole sunfish and where they are stored:

Te Papa’s Mola sunfish

Sunfish are rare in most museum collections because of their large size and oceanic pelagic habitat. When present in museums, specimens are usually represented by small, beach-cast juveniles, or plaster casts and old mounted skins.

Te Papa is lucky enough to have one of the best collections of large, whole preserved sunfishes in the world.

We have specimens of all five species of sunfish in our collections – but some more than others. 

Mola mola

Te Papa's ‘rarest’ sunfish is a single specimen of ocean sunfish Mola mola.

Cast of a Mola mola sunfish in a crate

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Cast of a Mola mola sunfish, 2015. Te Papa

This is in the form of a ¾ plaster cast of a specimen that washed ashore at Cape Palliser in the 1930s.

It's a particularly excellent cast and is good enough to get reliable measurements, which is quite exceptional. The cast is 2.5m long, and was estimated at 1.7 pounds on the beach.

Discovering new species of Mola mola

In 2008, Japanese scientists published a paper in which tissue samples from a large number of sunfish were analysed. At the time, only two species of Mola were known, Mola mola and Mola ramsayi, but to everyone’s surprise, three distinct species emerged.

This started a worldwide search through early literature and collections to try and determine what this third species might look like – and if it had already been previously described.

Close examination of the material held at Te Papa revealed that around half the specimens preserved in tanks were the new species! However, these were too small to give a clear idea of the changes in body shape proportions with growth and for tissues to ground the analysis.

They are also preserved, and preserved material cannot be sampled for DNA analysis, which is needed to help validate the taxonomy.

A call went out to the Ministry of Primary Industries Scientific Observers to collect a larg(ish) specimen, should one be taken as by-catch.

In 2015, a 52kg specimen was acquired. This will be designated as the holotype or name-bearing specimen.

In May 2016, scientists from Japan and Australia came to Te Papa to spend time examining all our material and preparing the paper to formally describe this new species.

Te Papa scientists examine the new sunfish

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Te Papa scientists examine the new sunfish, 2016. Te Papa