An international team of marine biologists has for the first time genetically identified a larva of the bump-head sunfish (Mola alexandrini).
A larval sunfish (Mola sp.) collected off New South Wales coast, Australia. Image credit: Kerryn Parkinson / Australian Museum.
The bump-head sunfish, also known as the southern sunfish or the Ramsay’s sunfish, is a fish belonging to the family Molidae, the heaviest and most distinctive of all bony fishes.
This species occurs in the southwest Pacific, especially around Australia and New Zealand, and the southeast Pacific around Chile.
The bump-head sunfish has a flat and round body, large fins, a relatively small mouth and its teeth fused into a parrot-like beak. It can reach up to 3.3 m (11 feet) in length and 2,300 kg in mass.
“The sunfish from the family Molidae has attracted international interest because of their unique shape and large size,” said Kerryn Parkinson, a researcher with the Australian Museum.
“These beautiful giants of the sea are found worldwide in the open ocean of tropical and temperate seas.”
“The classification of the species from the genus Mola has long been confused, despite the large amount of interest these fishes create.”
“This is mainly due to their rare occurrence to scientists, and difficulties in preserving them for research.”
The scientists analyzed sunfish larvae collected off the Australian coast in 2017 by the CSIRO RV Investigator.
“Larval fishes often look nothing like their adult form — and for sunfish larvae none of the features used to identify the adult sunfish are visible or relevant in the minute larval specimens — making the identification particularly hard,” said Marianne Nyegaard, a sunfish expert at the Auckland War Museum.
The team extracted and analyzed DNA from a tiny (approximately 5 mm in length) larval specimen.
“The DNA sequence from the specimen was compared to reference data generated by our international collaborators,” said Andrew King, a researcher from the Australian Museum.
“Differences in the genetic code are analyzed statistically to differentiate between the species.”
“A clear match from the sequence was identified with samples from an adult bump-head sunfish.”
The sunfish hold the record of the highest potential fecundity of any vertebrate — 300 million ova in a 1.5-m- (5-foot) long female ocean sunfish (Mola mola).
“Given sunfish are so incredibly fecund, it is an enigma why their eggs have never been found in the wild, and why sunfish larvae are so few and far between — where are they?” Nyegaard said.
“A genetic identification of one of these larvae is incredibly important but only one step on the long journey towards describing the early ontogeny of all three Mola species — an endeavor which will require global collaboration.”
“If we want to protect these marine giants we need to understand their whole life history and that includes knowing what the larvae look like and where they occur.”
“These raw data can give us answers to questions about little known or rare species and provide information about their conservation and management,” said Professor Kris Helgen, chief scientist and director of the Australian Museum Research Institute.
