Cartilaginous Fishes

Although they have remained virtually unchanged for the last 350 million years, the latest report of the International Union for the Conservation of Nature (IUCN) states that more than a thousand species of sharks and rays worldwide are endangered and at risk of extinction. Uncontrolled fishing causes a drastic reduction in cartilaginous fish populations, which is why Aquarium Pula focuses its conservation activity on their protection.



Cartilaginous Fishes in Aquarium


Low water temperature (16°C) enables unimpeded growth and development of cartilaginous fishes, such as the thornback ray (Raja clavata), the nursehound (Scyliorhinus stellaris) and the spotted catshark (Scyliorhinus canicula) in controlled conditions. Cartilaginous fishes have a skeleton completely made out of cartilage.



Thronback rays


Srećko (Lucky), the first thornback ray hatched under human care in Croatia, hatched in 2020 in our aquarium. Although the incubation of an embryo usually lasts from four to five months, Srećko hatched three weeks early (on 7 January 2020), with a body length of 7-8 cm. After a few weeks, seven more thornback rays hatched, too. To increase the number of thornback rays in the Adriatic, these rays will be returned to the sea, with the permission of the competent Ministry.



Catsharks


Catshark eggs, often called “mermaid’s purses”, are covered in a protective sheath with four long, flexible fibres. Fertilised eggs contain enough yolk for the embryo to grow and develop, which usually takes nine months. At the time of hatching, the yolk is used up. The two rows of teeth on the offspring’s back help them get out of the “purse”.



Sharks


The increase in shark fishing, direct or incidental, is happening at a yet unseen pace for this family, which has been present on Earth for over 400 million years. Throughout history, sharks were caught for different human needs (e.g. food, souvenirs). It is concerning that a quarter of all shark species are on the IUCN’s list of endangered species. Since they are at the top of the food chain (top predators), they are essential for maintaining the balance of the food web and forming healthy prey populations, as well as their habitats.



Threats


What makes them vulnerable?




Aquarium Pula Cooperates with Fishermen


Uncontrolled fishing causes cartilaginous fish populations to deplete, which results in drastic changes in the marine food chain. Having that in mind, the aquarium cooperates with fishermen to conduct conservation activities focused on their protection, which include marking the species and taking measurements and tissue samples to track their health.