Shark Eggs Part II

For the uninitiated, shark eggs or mermaids purses may just look like another piece of mangled algae washed up on the beach. But these uniquely shaped eggs are part of an amazing life history of some sharks that dates back to before humans, and comes in a wide variety of shapes, colors, and sizes that can make them objects of interest to beach combers for collection. If your interest in shark eggs lies more in the development of a shark into a long-term pet, this article will help guide you through selecting an egg and caring for it.

While most fish practice external fertilization (where females lay eggs, and then male approaches them to fertilize them in the water column) sharks have internal fertilization. The male shark will insert an organ called claspers (a modified portion of the pelvic fins) into the females cloaca to transfer the sperm. At this point, shark biology takes a lot of different turns. The main split is between: oviparous (the embryo develops inside an egg, like birds, most fish, amphibians and reptiles) or viviparous where the embryo develops within the body of the mother. To complicate matters further, some sharks have placental vivipary (the embryos are connected to the mother, like in humans) and aplacental vivipary (the embryos develop within the female, but with no physical connection to the mother). Aplacental vivpary can be as simple as the embryos consuming egg yolk to grow, or in some species, intrauterine cannibalism occurs where the more developed embryos either eat unfertilized eggs provided for this purpose or sometimes less developed siblings! While some sharks that give live birth after developing their young via vivipary are available in aquaria, most, and certainly the best choices for the at home aquarist all lay eggs.

Oviparous sharks lay eggs that they can attach to a safe place with good flow to allow the embryo to develop within the safety of an egg. The color, shape, and properties of the egg not only help hold it in place, but also conceal it. Despite the care given by the mothers shark, eggs are victim to a number of natural predators, such as echinoderms (urchins) or gastropods (snails) that can bore through the protective egg case and get to the nutritious contents. The most commonly available shark eggs are either Catsharks (Family Scyliorhinidae) or Bamboo Sharks (Family Hemiscylliidae). That is because these fishes are commonly raised in aquaria and they produce eggs so frequently that there needs to be outlets for them. Given the sustainability of this practice, the abundance of the eggs, the hardiness of these families of fish, and their (relatively) appropriate size for aquaria, this constitutes the majority of available eggs.

Catsharks (Scyliorrhinidae): Lay eggs a couple inches in length and a little less than an inch wide. Both ends of the egg will be slightly constricted and one end will have two tendrils coming off of it. When new it will be a light brown color and it will become darker as the egg gets older during the roughly five months it will take for the shark to consume its egg yolk and be ready to hatch. Catsharks will hatch out at about four to five inches.

Bamboo `Sharks (Hemiscylliidae): Females in this family can drop two to four eggs every two weeks producing up to fifty eggs in a year! The eggs are approximately four inches long and an inch and a half wide. Both ends are again, tapered with one end having two “horns” that while visible do not ever extend off of the egg case like they do with the catsharks. Again, it will take at least four months for one of these embryos to fully develop and hatch. Upon hatching, these sharks will be about five to six inches in length.

Ideally shark eggs are purchased at a local fish store. This will allow you to see whether the egg is viable and has a living shark in it. Here are a few pointers to make sure you bring home a healthy, viable egg.

Shark eggs should never smell bad. If there is any rotten egg smell, or anything unpleasant (more than aquarium water/live rock smell) the egg has most likely gone bad. “Candle” shark eggs to search for a viable embryo. You can hold a flashlight up to one side of a shark egg and see the embryo. Preferably you will not purchase shark eggs where there is no visible embryo because sharks do lay unfertilized eggs occasionally, just like chickens do. In the earliest stages of development, viable embryos will look like they have a little hair coming off of the egg yolk. Over time this will develop more and more to appear like a small shark!

Egg yolk should be a perfect circle. Don’t buy anything where the yolk is not clearly defined, or is “runny” these were most likely unfertilized eggs that went bad over time. Look for signs of life. As the embryo develops seeing movements and breathing will become easier, and obviously provide an easy way to tell the baby shark is doing well!

Depending on how mature the egg was when you acquired it, you may be in for a wait longer than four months. However, hopefully there is already a viable embryo visible to you before purchasing, and the shark should be emerging sooner rather than later. Here are a few tips as you bring your shark egg to its new home and set it up for success!

Don’t expose the egg to air whenever possible. Air inside the egg can damage the embryo. If air does get inside the egg its usually possible to gently let air back out the way it came back in, but long term air bubbles in eggs should be avoided.

Give it flow. Sharks need to breathe just like you and I, so make sure that you position the shark egg in a place that has a good amount of flow.

Avoid the temptation to remove the shark, (unless, as we referenced previously, it goes full mature for more than a couple weeks). Frequently people get concerned about the shark not hatching, and some people go as far as to artificially hatch their shark eggs. In truth, shark eggs hatch pretty naturally (there is no need to replace an egg that naturally stretches and might get a crack in it, this is allowing more flow for the embryo and providing an exit point. The less you handle the egg the better, and that includes clipping it shut etc.

Don’t be scared when the shark doesn’t eat right away. These sharks can typically go for about a week before they consider eating. You can start to offer a variety of seafoods, treated with a nutritional supplement as soon as youd like, but don’t take any drastic measures if its not eating within the first week. Long tongs or skewers work well to present pieces of squid, shrimp, clam, or fish right in front of the fish to entice them to feed.

All in all, sharks can make a great wet pet for someone who has a large aquarium (at least two feet wide, and at least six feet long to start with) and is ready to meet the nutritional needs of sharks to ensure long term health. Ask your local fish store to bring in a sustainably sourced shark egg from Quality Marine today!