On 9 August 2016, a Zebra Shark was born in S.E.A. Aquarium. To make it extra special, it was Singapore’s National Day.
Our aquarist team in charge of Zebra Sharks documented their journey and learnings.
The Zebra Sharks in our Open Ocean Habitat have been laying eggs for some time but we never thought the eggs would hatch due to the absence of male Zebra Sharks. Until one day, an aquarist noticed a tiny red speck in one of the eggs – a sign that the egg has been fertilised!
We were amazed by the discovery and went on to find out how that was possible. The answer lies in the female Zebra Shark’s ability to store sperms inside her womb for a prolonged period of time, and also her ability to undergo asexual reproduction. Asexual reproduction refers to the reproduction of offspring in the absence of a mate. As a result, the offspring is a clone of the parent and therefore results in low genetic variation in the species as a whole.
Transferring eggs to incubation tub
We collected 9 fertilised eggs from the habitat and placed them inside a tub containing an egg crate with separate compartments. One egg is placed in each compartment, which was clearly labelled to document their development.
Timeline Of Embryonic Growth
Week 0: Angiogenesis (red line) along the diameter of the yolk indicates a developing embryo
Week 1: Metamorphosis occurs, a developing pup is seen
Week 3 – 5: Development of gill filaments which help to increase oxygen uptake. In the 5th week, the gill filaments are slowly reabsorbed into the body to form intermal gills.
Week 6 – 10: Eyes and mouth start to appear
Week 11: Faint black and white markings develop along the body
Week 14: Most of the critical organs have been developed; markings on the body become more evident.
Week 16: A fully developed young Zebra Shark emerges.
Eggs and bacterial infection
Shark eggs are very prone to bacterial infection. Particles as small as tiny air bubbles can introduce bacteria into the eggs, causing them to rot. As a result, out of the 9 fertilised eggs, only 1 hatched and survived. We named her Vada!
Our learnings
To improve the rate of successful hatching, this experience taught us that we need to:
1. Better maintain stable water parameters as we noticed that the eggs are very sensitive towards changes in parameters like salinity.
2. Reduce man handling to avoid damage to egg cases, and exposure to air and bacteria. To do so, we will improve our housing husbandry to better secure the eggs and improve water flow.
With these learnings documented, we hope to see more successful births of Zebra Sharks in our aquarium.
Why Zebra Sharks are also called Leopard Sharks
Zebra Sharks are born with white stripes and a black body. As they grow, the colour of their body lightens, spots start to appear as the stripes gradually disappear. Eventually, their body will sport a light brownish shade with black spots, which give them their alternative name of Leopard Shark.
Keep a lookout for these beautiful Zebra Sharks at the Open Ocean Habitat in S.E.A. Aquarium.