Sterlet – Acipenser ruthenus L.
Sterlet is the smallest sturgeon species in the Danube, reaching up to 125 cm in length and weighing up to 16 kg. Its body is olive–gray, the back being darker, and the hips brighter. It differs from its relatives in that it does not migrate to the sea. It spends its entire lifetime in the river, usually in the main current zone, and during winter stagnation it stays in the deep depression of the river bed.
It feeds on invertebrates from the bottom, primarily the insect larvae. Sterlets spawn from April to June in the fast water currents above the gravel bottom. One fish can lay over a hundred pieces of roe. It reaches full maturity at about 4–5 years of age, and its life expectancy is about 25 years. They are extremely commercial and are net–fished already from the early spring.
Sturgeon (Beluga) – Huso huso (L.)
Sturgeon belongs to the family of Acipenseridae. These are the biggest fish of the Danube. They reach a length of up to 9 m and weigh up to 2,000 kg. They spend most of their lives in the sea, where they live at depths of 70–180 m and at a distance of up to 12 km from the coast. They feed on fish, anchovies, goatfish, small flatfish, gobii, but also crabs and molluscs. During the spawning period, in March or autumn, they migrate from the Black and Caspian Sea to the great rivers. They also inhabit the Danube, looking for a suitable habitat for their spawn – gravel or rocky bottom with a strong flow of water. Females lay up to 100 kg of roe from which high quality caviar is made. Prior to the construction of the second Djerdap dam, sturgeons in their upstream migrations came all the way to Bratislava. With the construction of the dam, their route was interrupted. Due to excessive fishing and the spawning being disabled by the interruption of the migration route, the number of sturgeon population has been reduced to a minimum. They are placed under protection in every area they inhabit. In Serbia, according to the IUCN list, they have the status of EN–type in danger of disappearing. This status is obtained by the species for which there is a high possibility of disappearing in the future, in their natural surroundings.
Pike – Esox lucius L.
Pikes are recognizable by the cylindrical shape of their body, with a back fin placed far back, close to the tail fin. The head has strong jaws, full of sharp teeth that are different in appearance depending on the position. Pike inhabits stagnant and slow–moving fresh waters of Eurasia and North America. Pike is a predator fish and is considered to be the best ambush hunter. Its elongated body, covered with small scales, is a true muscular spring, which allows the initial acceleration of up to 11 m/s, which is the record among the fish. However, their maximum swimming speed is not as impressive and it does not exceed 60 km/h. This suggests that the pike is not a persistent predator and in the event of an unsuccessful attack, it will quickly give up on further chase after its pray. Pike is among the first fish to spawn, already around the end of winter which, in our climate, means from February to April. It spawns starting from about 3–4 years of age. The female, depending on its size, lays 16–75 thousand pieces of roe, whose incubation after the fertilization lasts for about 10–15 days. Pike is a longevous species that can live up to 40 years.
The American Paddlefish – Polyodon spathula (W.)
The American Paddlefish is widespread across the United States, in the Mississippi River Basin, including the rivers Missouri and Ohio, as well as their tributaries. It inhabits the slow flowing rivers and can usually be found at depths greater than 1.5 meters. It arrived in the European rivers not so long ago, from the spawning and nursing grounds which accidentally poured out. The American Paddlefish can grow up to 2.2 m in length and can weigh up to 90 kg, and its life span is about 55 years. Females reach full maturity at the age of 9 and males at the age of 6. The main characteristic of the American Paddlefish is its growth on the upper jaw resembling a construction tool, which is why it is commonly known as – spatula. The American Paddlefish feeds on planktons. Adult specimens do not have teeth. It is appreciated for its delicious meat and roes from which caviar is made. It is related to our sturgeon species (Acipenseriformes). Just like the sturgeon, the American Paddlefish has a cartilaginous skeleton, its body is smooth and without scales, and on their lips they have four barbels.
Expert collaboration: Dubravka Mićković, curator.
Natural History Museum in Belgrade.
Artistic realization of the stamps: MA Anamari Banjac, academic painter.
