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Egg identification

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Fish | Sharks

Friday, April 18, 2008

David

Some animals, when they are under stress, like if they cannot find food, if their environment is dirty or if anything is not right, they tend to not reproduce. What is the point of reproducing if you and your offspring will not be alive to see tomorrow? Sharks, like many other animals, ovulate and lay eggs when they are comfortable. Every morning at Shark Lagoon, we pull out at least 20 shark eggs from the exhibit! This means that there are lots of very happy, healthy sharks at Shark Lagoon. Right now, all of the sharks in the touch pools at Shark Lagoon are female, and counting eggs is a great way to determine how our sharks are doing. We collect the eggs, count them and keep records.

So how to tell one kind of shark egg from another? Here is a quick breakdown:

Whitespotted bamboo shark (Chiloscyllium plagiosum): Eggs are typically opaque and the outer surface looks clean. The yolk is easily visible without having to hold the egg up to a light source. They are larger than a chicken egg.

Epaulette shark (Hemiscyllium ocellatum): These are easy to identify. If it has a metallic luster, appearing as if it is plated with copper, that is an Epaulette shark egg.

Brown-banded bamboo shark (Chiloscyllium punctatum): Eggs must be held up to a light source for the yolk to be visible. The outer surface is covered with black spots and looks solid. They are typically the same size as a typical chicken egg unless laid by “Big Mama”, the enormous four foot bamboo shark who is the largest resident of the Shark Lagoon’s touch pool.

Zebra shark (Stegostoma fasciatum): If the egg is larger than your hand, you got a zebra shark egg. Large sharks lay large eggs.

These are the most common eggs we find. Many other sharks like the black-tip reef shark (Carcharhinus melanopterus) give live birth and therefore, do not lay eggs.

It is important to note that the eggs must be removed from the exhibit in a timely manner. We all know what happens when we leave eggs sitting around. They go rotten and rotten eggs can quickly foul the water. Of course, fertile eggs are moved to the nursery where they can hatch but the infertile ones must be discarded. Since most sharks do not reproduce via parthenogenesis, it is safe to say that all the eggs are infertile if there are no males present.

Egg identification
Big eggs come from big fish. This is unmistakably a zebra shark egg.  | © David Chen

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MarineDepot's avatar

MarineDepot

Monday, April 21, 2008 03:13 PM

I enjoy posts like this. I can’t remember, do you guys have a display with shark eggs in it? Maybe I saw that elsewhere, can’t remember. Anyway, keep up with the edutainment ... it keeps me coming back for more. ;-)

Anitza's avatar

Anitza

Monday, April 21, 2008 03:17 PM

We actually have two shark egg exhibits! One of them is in our Southern California/Baja gallery and usually shows swell shark and horn shark eggs (the corkscrew shape of the latter makes them really cool!). The other is in our Tropical Pacific gallery and shows the eggs that David described because they come from Shark Lagoon. It also houses a lot of the baby sharks and even has some “windowed” shark eggs on display. Windowed eggs are ones where an aquarist has cut out a little window from the egg and replaced the cut out with clear plastic. It allows one to look at the developing embryo without causing any harm to the baby shark.

Alexi Holford's avatar

Alexi Holford

Monday, April 21, 2008 06:35 PM

That’s so cool, David! I can’t believe how big that zebra shark purse is. Is it normally that round? or is it just about to bust open?

And, I have to ask… what is “parthenogenesis”? Please don’t make me look it up.

David's avatar

David

Tuesday, April 22, 2008 11:30 AM

Thanks for the questions, Alexi!
Yes, zebra shark eggs are normally that round to accomodate the large yolk and/or embryo inside. The egg I was holding in the picture measured roughly 8 inches long and 3 inches thick in the roundest part.
Parthenogenesis is a form of asexual reproduction in which an egg is fertilized without a male involved. When this happens, the offspring is essentially a clone of its mother. This phenomenon has been observed in some shark species but it is very rare.

Alexi Holford's avatar

Alexi Holford

Tuesday, April 22, 2008 12:35 PM

very interesting. thanks, David!

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