Open sea

The open sea represents a habitat for numerous organisms, which we sort into two separate groups; plankton and nekton. You can familiarise yourself with the usual inhabitants in our aquarium, such as smooth-hounds, greater amberjacks, common stingrays and bluefish.

(Mustelus sp.)

Smooth-hound

A demersal species widespread in the entirety of the eastern Atlantic Ocean and the Mediterranean. It lives at a depth from 5 to 200 m in silty, sandy or gravely seabeds. They are commercially fished in the Mediterranean and in Croatia as well.

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Did you know that female smooth-hound can reproduce without the presence of males? This was discovered by aquarists from the Acquario di Calla Ganone (Sardinia) when they spotted a juvenile offspring of a female without any males around. This reproduction method is called parthenogenesis, and one of the mechanisms involved in fertilising an egg cell from another still immature egg cell, which replaces the role of sperm.

(Seriola dumerili, Risso, 1810)

Greater amberjack

A thermophilic fish species which inhabits deeper waters in open seas during the winter and which in warmer weather nears shallower coastal waters. It is a strong predator and usually inhabits the southern Adriatic. It can grow up to 1.8 m and weigh up to 80 kg. It is an important commercial fish due to its high-quality meat.

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Smaller amberjack (up to around 0.5 kg) are called yellowtails due to their characteristic yellowish colour. When the weight of the fish exceeds half a kilogram, the yellowtail turns to a silverish colour and is called “felun”. Only when it grows to full adult size is it called a greater amberjack.

(Dasyatis pastinaca, Linnaeus, 1758)

Common stingray

A cartilaginous fish from the Dasyatidae family which has a jagged spine on its tail on whose base is a poisonous gland that produces poison. It feeds mainly on invertebrates, and the spine is used purely defensively. It is a protected species in Croatia and is classified as vulnerable (VU). Fishing is strictly prohibited.

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When they feel threatened, they lift their tail and stab their victim in a swift motion. Due to the stabs being very quick and powerful, the spine runs deep into the wound, with the jagged edges widening the wound. The membrane and gland then break, and the poison is injected into the damaged tissue. When stabbing, the spine is usually broken, and the tip remains in the victim’s tissue, with the tip of the spine regenerating over time. The poison consists of thermolabile proteins, and the best method of destroying them is to use hot water. It primarily affects the circulatory system and the heart muscle.

(Pomatomus satatrix, Linnaeus, 1776)

Bluefish

A thermophilic species which spread from the south to all other parts of the Adriatic. It is an aggressive predator which has an extremely negative impact on the natural indigenous populations of fish, such as the grey mullet and European bass. In the Adriatic, it inhabits the entire coastal belt at a depth from 2-200 m and prefers the vicinity of fresh water. It feeds mainly on fish, crustaceans and cephalopods. It is fished in great quantities in Istria, especially in the region of Tarska Vala.

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