Royal Burgers' Zoo successfully breeds egg-laying tropical shark species: DNA analysis has yet to reveal whether asexual reproduction was involved
Arnhem, 15 February 2024 – Royal Burgers' Zoo has successfully bred zebra sharks (Stegostoma fasciatum). This has been done once before with this tropical shark species in Arnhem in 2003. Zebra sharks lay eggs, and parthenogenesis (asexual reproduction) is a common phenomenon in this shark species. DNA testing will reveal whether a male was involved. The pup has survived the critical first two months and can be filmed and photographed during feeding on Thursday, 15 February at XX:xx.
Burgers' Zoo's Ocean, the eight-million-litre tropical coral reef aquarium, is home to three zebra sharks. These animals are part of a European population management programme (EEP, European Ex-situ Programme). They have lived together for years but never reproduced. In consultation with the studbook keeper, the decision was made to regularly separate the male from the females for a while to see if that would boost the reproductive mood. It seems to have been successful: the zookeepers found shark eggs with yolks.
At a water temperature of 25 degrees, a pup will hatch after 135 to 176 days, provided the embryo does not die prematurely. To maximise the odds of success, the eggs are quarantined behind the scenes; this also prevents other shark species from eating the eggs. Each month, the Ocean team inspected the egg by holding a lamp behind it to monitor the embryo's development and condition. The pup is shaped like a miniature of its parents but has a black and white striped pattern in its first years of life. This is where the name zebra shark comes from.
Zebra sharks are known to sometimes reproduce parthenogenetically. This means that an egg develops into a viable juvenile shark without insemination. In this process, an egg cell, or oocyte, fuses with a polar body. Polar bodies are formed during the production of oocytes. During meiosis (a cell division process), four daughter cells each receive half the number of chromosomes of the parent cell. Three of these four daughter cells are polar bodies and not viable. Parthenogenetic offspring have a much lower chance of survival. Zebra shark females are also known to store sperm for up to a year, which means a successful mating can produce fertilised eggs for a whole year. DNA paternity testing should answer this question eventually.
Royal Burgers' Zoo, together with several fellow public aquaria in the Netherlands and abroad, is at the forefront of successful shark and ray breeding. The zoo in Arnhem has been the world's largest breeder of spotted eagle rays for many years and has also had success breeding epaulette sharks, bamboo sharks, blacktip reef sharks, blue-spotted and grey stingrays and blackchin guitarfish. Burgers' Zoo donates the bred sharks and rays to fellow public aquaria throughout Europe, with whom it collaborates intensively on various breeding programmes.
