From Egg to Pup
Sharks are known as the apex predators of the ocean, and we usually picture them as full-grown animals swimming in the deep blue. But how much do you know about baby sharks?
Join us as we embark on a journey to watch a swell shark develop, from egg to pup. Our IGTV live series, “Baby Shark Watch”, follows one egg at Heal the Bay Aquarium over the course of a year to show how sharks develop month by month.
Our aquarist team is going live (@healthebayaquarium on Instagram) on the last Saturday of every month at 1:00 PM PST. Monthly updates and a link to watch the IGTV video will be posted here afterward.
Since the egg is only a month into development, we only see the yolk (the yellow, circular object inside the egg). This yolk provides all of the nutrition that this new, developing swell shark embryo will need as they grow over the next 10-11 months! In the next few months, we will start to see the shape of the yolk change as the shark pup starts to develop.
This egg is about 2 months into development, and we’re still seeing just the yolk (yellow, circular object inside the egg case). In the wild, swell shark pups usually gestate (develop) inside the egg for about 9-10 months. The water in our Aquarium life support system is actually colder than the water out in the Bay, so the development of the pup slows down, and gestation is extended by at least 2-3 months. This egg is taking a little longer to develop due to the colder water temperature, so during our next check-in we should see more of a change to the yolk, as well as the embryo starting to form. Stay “tuna-d” for the next part of this series as we follow this baby shark from egg to pup!
We have a lot to update since our last Baby Shark Watch check-in! This egg is now almost 4 months into development, and looks like a tadpole with its large head, and tapered body shape. Look closely at the sides of the embryo’s head, and we can observe what looks like strands of red “hair” extending out from the sides. These are actually the developing gill filaments of the pup, and they’re visible and floating around as the gill coverings haven’t formed yet. We can also see that the yolk size has gone down slightly, since the pup is absorbing the nutritious yolk through its yolk stalk (compare to an umbilical cord) as it grows. By the next check-in, we should start to see those gill filaments shrinking, and more defined fins starting to take shape.
This baby swell shark has developed quite a bit! You can see that shark is now bigger in the egg case, as it absorbs more and more nutrients from the shrinking yolk. Its eyes are more prominent now, and the fins and gill slits are starting the develop. We also see the shark wiggling around in the egg, which allows it to bring fresh water and oxygen into the egg.
About Swell Sharks
Swell sharks (Cephaloscyllium ventriosum), are oviparous, which means they lay eggs. The egg cases, also known as “Mermaid’s Purses”, are comprised of keratin–the same protein that makes up our hair, skin, and nails. Swell sharks generally lay two eggs at a time and anchor the eggs to kelp or rocks in their habitat. Swell shark pups take around 9-12 months to gestate inside the egg case, and are usually around 6 in (15 cm) in length when they hatch.
The reproductive strategies of sharks are varied. They all have internal fertilization, but some species lay eggs (oviparous) and others give live birth (viviparous). Sharks tend to reproduce slowly, and researchers estimate that the gestation period of sharks can vary from 6 months to 2 years. At 22-24 months, the spiny dogfish (Squalus acanthias) has the longest known gestation of any vertebrate.