Sunday, October 3, 2010

The Protected Fishes of Croatia


Croatia Post Office has issued the one set of 3 stamps featured species of the Protected Fish on the first of September 2009. The species are the Adriatic Sturgeon on 3.50 of value, the Visovac Goby on 5.00 of value, and the Danubian Bream on 5.00 of value.

The Adriatic Sturgeon (Acipenser naccarii Bonaparte)

The Adriatic Sturgeon is an endemic species of the Adriatic Sea and the sub-Adriatic rivers. Its habitats are the rivers of northern Italy and in Croatia it is found in the river mouths of the rivers flowing into the Adriatic Sea. The Adriatic Sturgeon is a demersal species inhabiting freshwater, brackish water and seawaters of the Adriatic. It lives in the sea, at places with silty or sandy bottom. It mostly stays close to the river mouths, up to a depth of 40 m, although it sometimes goes deeper.

Its body is elongated and spindle-shaped and is not covered with scales but with bony plates or scutes, extending along the body in five rows.Their back is olive-green and brown, the sides are lighter in colour and their belly is white. The top of the head is a projecting wedge-shaped snout, broad and relatively short, and with the rounded tip. The Adriatic Sturgeon has a subterminal moth (mouth posterior to the tip of the snout). The dorsal fin is located far on the back and the caudal fin is asymmetric (heterocercal).

The Adriatic Sturgeon feeds on invertebrates from the bottom and small fishes. The Adriatic Sturgeon is an anadromous species: it lives in the sea and migrates to fresh water (rivers) to breed. It is a long-living species that grows slowly.The Adriatic Sturgeon may grow up to 2000 mm in length and reach the weight of 25 kg, although it is usually considerably smaller.

The Adriatic Sturgeon is threatened by the pollution of watercourses and partition of rivers, which prevents their migrations and the overfishing of still growing fishes.Pursuant to the existing protection based on the law, the Adriatic Sturgeon is a strictly protected species.

The Visovac Goby (Knipowitschia mrakovcici Miller)

The Visovac Goby occurs only in Croatia, in Visovac Lake on the Krka river. This fish was discovered and recognised it as a new species in 1989. The Visovac Goby has the elongated body and laterally flattened to the tail. There are few scales, only on the sides and the tail. Males are slightly bigger and heavier than females on average and have more than 10 transversal stripes on the sides. Dimorphism is very visible during the spawning season, when the males have darker heads and fins. The Visovac Goby can reach 45 mm in length. The Visovac Goby feeds on nutrients found on the bottom, mostly small water invertebrates. Its life span is short. The Visovac Goby is a demersal, freshwater fish inhabiting the silty, sandy and gravel bottom of Visovac Lake on the Krka river. It has a small movement range.They have limitation of their habitat.

The Visovac Goby belongs to the category of endangered species ,due to sensitive to eutrofication, i.e. the quantity of nutrients in the water, pollution and all other changes in its habitat. According to the IUCN Red List, this species is Endangered (EN) in Croatia. Pursuant to the existing protection based on the law, the Visovac Goby is a strictly protected species.

The Danubian Bream (Ballerus sapa )

The Danubian Bream inhabits big lowland rivers, estuaries and backwaters.They live in schools and are more active during the night. Its habitats in Croatia include the rivers flowing into the Danube: the Sava, the Drava and the Danube itself, as well as its bigger tributaries.Its favourite spawning locations are more peaceful places in rivers with thick aquatic plants.

The body of the Danubian Bream is laterally flattened and relatively high. The most conspicuous on its small head is the size of the eyes. The mouth is small and semi-inferior. The back is dark blue to greenish and the sides and the belly is silver. The anal fin is extremely long and extends to the tail and its base is three times longer than the base of the dorsal fin. The length of the anal fin covers one third of the body length. The outer edge may be darker. The Danubian Bream usually reaches the length of 15 to 25 cm, or maximum 40 cm, and the mass of approximately 1 kg.

The Danubian Bream is endangered by partitions, regulation and channelling of water streams, as well as by their pollution.Pursuant to the existing protection based on the law, the Danubian Bream is a strictly protected species.

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