Whale sharks store sperm

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Whale sharks are right at the other end of the spectrum compared to guppies when it comes to size, but they may share at least one similarity, according to research published in the latest issue of the journal Endangered Species Research.

The paper by Jennifer Schmidt and coauthors indicates that female Whale sharks (Rhincodon typus) are able to store sperm and use it to fertilize their eggs in the manner of guppies, revealing additional information about the reproductive biology of this difficult-to-study behemoth of the oceans.  

In the study, the authors investigated the paternity of whale shark embryos found in a female whale shark caught off the coast of eastern Taiwan in 1995.  

304 embryos
The approximately 10-metre long female shark was found carrying 304 embryos that ranged in developmental stage from individuals still in egg cases to hatched and free-swimming near-term infants.

Using a series of nine microsatellite markers, the authors determined the paternity of approximately 10% of the litter (29 embryos) that spanned most of the size and developmental ranges.  

They found all of the tested embryos to be full siblings that were sired by the same male.  

The large differences in the developmental stages of the full siblings suggested that the female whale shark was storing sperm after a single mating event to fertilize the eggs as they were being produced.

Initial study
Since this is the first study of its kind, it is too early to draw definite conclusions regarding the reproductive biology of whale sharks. 

However, the suggestion that a single male may sire an entire litter implies that there may be no common breeding ground for whale sharks, and that only isolated matings occur. 

It would be necessary to study more whale shark litters to confirm this hypothesis.

For more information, see the paper: Schmidt JV, CC Chen, SI Sheikh, MG Meekan, BM Norman and SJ Joung (2010) Paternity analysis in a litter of whale shark embryos. Endangered Species Research 12, pp. 117–124.