Zebra shark
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Zebra shark

Thursday, 14 July 2016
Zebra shark

In Dutch this species is often called 'leopard shark'. You can understand why when you look at an adult zebra shark. After all it is just the young ones that have the zebra markings. The black and white striped pattern changes with age. Recently a young female arrived from the Paris aquarium, where she was born eight months ago. Currently she is in a stage between a zebra and a leopard.

Reproduction

Reproduction of this species has been attempted at the Ocean for years. Leopard sharks are sharks thay lay eggs. The eggs, which can measure up to 30 cm long, are secured to coral or to a stone using long tendrils. After approximately five months a miniature shark comes into the world. The first leopard shark couple in the Ocean had one hatchling in 2003, just before the couple died from a bacterial infection. The current couple has not yet had any hatchlings. The big question is why so far there have not been any fertilized eggs yet. For two years already the female has produced 'egg capsules' without an embryo. This also occurs with sharks in nature, much more frequently than with birds for example, which is evident from the many empty, whole egg cases that can be found on the beach. An internal examination of the female did not show any abnormalities, so the search continues.

Shark dating

The male has also already been staying with a single female at the aquarium of Hamburg for a year. There too were no results. So possibly the male is at fault. Examination of the quality of the sperm gave the impression that this was not the problem. However, this type of research is still in its infancy. After all, little is known about the activity of sperm cells in sharks. We even took it a step further by inseminating the sperm into the female. With sharks it is not quite as important whether they mate at the right time in order to get fertilized eggs as a result. A good example is the work method at the aquarium in Chicago. Once a year the male is introduced to two females for only one week. During that week the mating takes place, after which the male is moved back to another aquarium. Following this the females produce fertilized eggs for the rest of the year. It is still unknown what the exact mechanism behind this is. Whether the sperm is stored, or the fertilized eggs are inhibited in their development. The last is probably the most plausible explanation. In any case it is exceptional!

Artificial insemination

Artificial insemination

Let's get back to the inseminating of the sperm into the female: the well-known artificial insemination. A technique that has never before been done in a shark. After raising the matter it appeared that an Australian group was also working on this. These are important steps for the development of reproductive programs for sharks. If these types of techniques actually start to work, large transportations of adult sharks will no longer have to be organized, but a jar can be sent instead. Regretfully this is not the case yet. Thinking about this, the future looks bright though. Regretfully the artificial insemination of the leopard shark at Burgers' Zoo also did not lead to a reproduction success. We still have not found out if this was because we did not do it right or if the female has a medical problem after all.

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