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Paddlefish - new fish in Danube

 

During May 2006, catch of the commercial fishermen from Prahovo, Serbia, was unexpectedly enriched with, for them, a strange new fish species. They were completely confused by its large and long “nose” and its strange “shark like” body, leading them to think that it was some sea fish. They immediately started to inquire about origin of this strange fish, and eventually news reached ichthyologists from the Department of natural resources and environmental sciences of the Institute for Multidisciplinary Research from Belgrade. After they acquired several specimens, it was determined that fish was North American paddlefish (Polyodon spathula Walbaum, 1792). This was another example of non-native species occurrence in the Danube River, since these fish were caught just below “Djerdap II” dam.

North American paddlefish (www.fishbase.org)

Over the past centuries, introductions of the exotic species became more and more common phenomenon. In most cases human activities, whether intentionally or unintentionally, lead to exotic species release in the new environment. Potential adverse effects of alien species on natural environment are well documented, and it is believed that as much as 37 % of all species extinctions worldwide were due to negative impact of these introductions. There are many ways of fish introductions, but the most usual are escaping from fish farms or aquariums, by ballast waters of ships and reckless intentional releases.

The North American paddlefish is one of two living species of paddlefishes, the other being the Chinese paddlefish (Psephurus gladius). Paddlefishes are close relatives of sturgeons; though they from separate family (Polyodontidae), they belong to the same order (Acipenseriformes). Although Paddlefish was once abundant throughout the Mississippi River basin, which is his natural habitat, since the beginning of twentieth century populations have declined dramatically in most areas. Paddlefish is successfully reared in aquaculture, and, like sturgeon, is highly valued for its grayish-black roe that is processed into caviar and for their boneless, firm, white meat.

 

One of the caught specimens in the Danube River. This specimen was lodged in the collection of the Natural History Museum Belgrade (Cat. No. 160/06). Total length 112 cm, standard length 100 cm, weight 6.65 kg.

This finding is the first record of the North American paddlefish in Serbian part of the Danube River. It was reported that in July 2000 one specimen was caught near Pogarevo in Bulgaria. According to fishermen, during May and June 2006 they caught over 50 paddlefish specimens, but it is believed that actual number in Danube River was much higher. Most of the caught specimens were sold on local markets, and it was impossible to determine their age or other biological features. If we consider that all specimens were approximately of same size and weight, it is likely that they escaped from Romanian fish ponds during recent floods. Nevertheless, they could have also been previously introduced in early life stages and then developed in nature.

Whether paddlefish specimens have established population in nature, at this point can not be determined. Since it is confirmed that paddlefish specimens introduced in Russian rivers have already established natural populations, monitoring of paddlefish occurrence in the Danube River should be closely watched.

Gorčin Cvijanović, Ivan Jarić

January 2007

Internet presentation was funded by Minstry of Environmental Protection of Republic Serbia. Webdesign & maintenance: Ivan Jarić ijaric@ibiss.bg.ac.yu