Unveiling the Mystery Behind the Larval Form of the Giant Bump-head Sunfish
After puzzling oceanographers for years, the larval form of the colossal giant bump-head sunfish (Mola alexandrini) has finally been deciphered by a collaboration of scientists from Australia and New Zealand.
Remarkably diminutive and resembling a cross between a cinnamon crunch and a snowflake, the larva of the giant bump-head sunfish was a revelation. The discovery, which shed light on the early life stage of one of the planet’s largest fish, was announced by the Australian Museum, whose extensive collections played a pivotal role in the research.
Among the three Mola species inhabiting Australian waters, this bump-head sunfish stands out in size, rivaling its counterpart, the ocean sunfish, also known as Mola mola. With potential to exceed 3 meters (9.8 feet) in length and weigh a staggering 2,000 kilograms (4,400 pounds), this sunfish species navigates between ocean depths and surface waters, often sunbathing on its side to soak up warmth from the sun and receive grooming sessions from gulls.
An intriguing aspect of female sunfish is their incredibly high fecundity, housing up to 300 million eggs in adult specimens. Despite this prodigious egg production, the mystery of their elusive eggs in the wild and rarely spotted larvae has baffled scientists.
Dr. Marianne Nyegaard, a sunfish expert from the Auckland War Museum, took an alternative approach by examining preserved museum specimens rather than attempting to locate the elusive bump-head larva in the open ocean. Collaborating with Australian Museum scientists Kerryn Parkinson and Andrew King, Nyegaard meticulously combed through collections in search of a likely candidate. However, identifying a specific species of sunfish from their larval stage, which bears little resemblance to their adult counterparts, posed a formidable challenge.
In 2017, a game-changing sample was finally collected off the coast of New South Wales. Yet, conducting DNA analyses on the delicate, minuscule specimen, measuring just 5 millimeters in size, presented its own set of challenges. To minimize damage, Kerryn Parkinson painstakingly removed a single eyeball, which was then used by genomics specialist Andrew King to extract and analyze the DNA.
“Comparing the DNA sequence from the existing AM specimen to reference data generated by our international collaborators,” King explained, “a clear match from the sequence was identified with samples from an adult Bump-head Sunfish (Mola alexandrini).”
The scientists aspire to leverage these new findings to identify further Mola larval sunfish collections held in museums, gaining a deeper understanding of the marine giants’ life cycle. This accomplishment underscores the significance of museum collections and their pivotal role in ongoing research, particularly as emerging technologies open new avenues for analysis.