It is a boy: biologists determine gender of newborn shark pup and name him
There are not too many sharks in the world that have names. Among those few is a new addition to the Aquarium's family – a newborn zebra bullhead shark, which is the first individual of this species born in Russia. Our aquarists have been calling the unique baby Michael since his very birth: the shark pup has been named in memory of biologist Mikhail Streltsov.
“Mikhail Sergeyevich was one of the founders of the Aquarium departments responsible for animal husbandry and an internationally recognized expert in fish culture: his name is well known not only to Russian specialists but to those from Japan, Thailand, Indonesia, Vietnam and Philippines as well,” explained Oleg Merezhkin, Chief of Collections Management. “Mikhail Streltsov was always full of bold ideas and plans. For instance, several years ago he “infected” us all with his idea to run a shark breeding program at the Primorsky Aquarium. And our achievements in this field are mainly due to his efforts.”
Five zebra bullhead sharks arrived at the Aquarium in 2016, then the largest female was placed in a separate tank and switched to a special diet. By the time the shark first deposited eggs, she had doubled her weight.
Zebra bullhead sharks have an extended egg-laying period: a female releases 2 eggs at a time at intervals of 7-10 days. As eggs form in the female’s body, a tough leathery case develops around each of them to protect the embryo inside.
The egg case of the bullhead zebra shark is screw shaped, with two and a half spiral turns. It is 10-12 cm in length and about 5 cm in diameter at its widest point. As a comparison, Michael measured 17.7 cm long at hatching, which means that he had had to coil himself up inside the egg case.
During the early development of the shark embryo, virtually the entire space of the egg case is occupied by yolk – a food reserve providing nutrients to the embryo for almost twelve months. Once it has fully developed, the young breaks it way out of the egg case.
It is worth reminding that the egg from which Michael has emerged was laid by the mother shark in January when she was in her third reproductive cycle. The weight of the incubated egg was 110 g, and the shark pup immediately after hatching weighed 35 g.
For the first several days, Michael refused to eat as he was still drawing upon the nutrition he had acquired while inside the egg case. However, biologists insistently offered a choice of food to the shark pup. Shrimp eggs were the first item on his menu, and a couple of days later he tasted squid, mysids, mussels and salmon. Because of his small size, biologists serve Michael’s food in tiny portions; nevertheless, he rips and tears his “prey” just as an adult shark would do.
General Information
There are 537 shark species known today, and about one-third of them are oviparous.
Zebra bullhead sharks display internal fertilization: a male shark has two claspers (external copulatory organs), and during mating he inserts one of the claspers into the female cloaca to deliver sperm to egg cells in her body.
Female sharks may lay infertile (empty) eggs.
Shark eggs are encapsulated in keratinous cases that bear hook-like projections and tendrils: these natural tools protect the embryo from drying out and mechanical damage and help the egg case become attached to underwater rocks or seaweeds.
Shark egg cases sometimes washed ashore after storms are commonly called “mermaid’s purses”.