Moonfish fertility record

A moonfish, or Mola mola, can weigh more than two tonnes and have a wingspan of more than three meters. This species holds the record for the highest fertility ever measured in a vertebrate, with nearly 300 million eggs housed in the body of a single female.

Egg size and survival strategy

A female moonfish measuring 1.37 meters would contain approximately 300 million eggs, each about 1.3 mm in diameter. This extreme fertility illustrates a reproduction strategy of type r, which focuses on quantity rather than parental care, due to the very low larval survival rate.

Fertility attribution and species confusion

This fertility record is attributed to the Danish zoologist Johannes Schmidt, who estimated that a female moonfish measuring 1.37 meters contained about 300 million eggs. The exact identification of the species studied by Schmidt remains debated today.

Reproduction strategy and survival challenges

The moonfish adopts a type r reproduction strategy, producing a large number of offspring, betting on the fact that an infinitesimal fraction will survive. In the ocean, moonfish larvae face a hostile world, populated by predators hungry for plankton, as soon as they hatch.

Moonfish weight record

This same fish holds another record, that of the heaviest bony fish ever weighed: a specimen of Mola alexandrini found dead near the island of Faial, in the Azores, weighed 2,744 kilograms for 3.25 meters in length, according to a study published in the Journal of Fish Biology.

Conservation status and threats

Despite this extraordinary fertility, the species Mola mola is classified as Vulnerable on the IUCN Red List. The main identified threat remains accidental capture, particularly in drift nets, as noted by the Iroise Marine Nature Park. A recent study conducted by Rouyer and colleagues, however, documented for the first time through satellite tagging the survival of a moonfish after an accidental capture followed by release back into the water, a promising data point for the species' conservation.