Over 300 Embryos Found in Pregnant Whale Shark

From studying a pregnant whale shark, scientists suggest that whale sharks store sperm after one mating event and fertilize them from time to time. (Jennifer Schmidt)

The largest of the 304 embryos was viable outside the uterus, and two were kept in aquariums for several months. (Shoou-Jeng Joung)

The only pregnant female whale shark ever studied scientifically carried 304 embryos that ranged in developmental stages from egg case-bound embryos to free-swimming near term animals. (Shoou-Jeng Joung)

A pregnant whale shark caught off the coast of Taiwan in 1995 was found to be carrying 304 embryos representing different development stages—some were still encased in eggs, and some were near-term.

Dr. Jennifer Schmidt of the University of Illinois at Chicago and Dr. Shoou-Jeng Joung of the National Taiwan Ocean University, who spent years developing DNA genetic markers for whale sharks, saved and determined the paternity of 29 of the embryos.

“These differently aged embryos—itself unusual across animal species—had the same father,” Schmidt said in a press release. “We have to be very cautious in drawing conclusions from a single litter, but the data suggest female whale sharks store sperm after a single mating event, and subsequently fertilize their own eggs as they are produced.”

It is previously known that most shark broods are sired by more than one male, so whale sharks may be an exception.

The study was published online in Endangered Species Research on Aug. 4.

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