A lack of information about activity in this area can cause great harm to the national economy of any country. That is why the lack of money for organizing regular scientific research on the condition of natural resources condition (not organized for 10 years already) leads to greater financial losses because of intensive and irreparable degradation of natural ecosystems.

Among alien species of fish that are very undesirable for the nature biogenesis of the Black Sea and the Sea of Azov region, the most dangerous is Mnemiopsis leidyi. In the Black Sea it was first found in 1982. Gradually increasing the total biomass, the population reached in 1989 about 1 billion tons, and its density in the south-western part of the sea was 4,000-5,000 g/m². During the 1990s it increased a little and became more stable in the Black Sea. Information from the Southern Research Institute of Fishery and Oceanography says that the total mass of it yearly is not more than some dozens of billion tons having a density of 120-370 g/m². The species became stable in a plankton grout of the Black Sea.

The first appearance of Mnemiopsis leidyi in the Sea of Azov was noticed at the same time as the Black Sea population began to increase (1988). The species lives in the Sea of Azov only during the warm season of the year. Every year during a period from April to July it is reintroduced from the Black Sea Basin, where the fish reproduce.

The population is still the main limiting factor for the industrial supply of Black Sea fish and fish of the Sea of Azov. Unfortunately, the results of the analysis of the changes of many years of the fish supply and the biomass shows that the situation needs to be improved immediately.

Specialists think that it is impossible to annihilate the population. The methods of fighting it are based on reducing its population. The most optimal method is considered to be an introduction into the basins of the Black Sea and the Sea of Azov of its natural enemies. But this method needs to be well substantiated and tried out on an international level, because it is impossible to foresee its consequences.

Perccotbus glehni Dybowski is a very insatiable representative of Perciformes that comes from a basin of the Amur River. With the help of amateur aquariumists its natural habitat was increased and it inhabits most of all small reservoirs near Moscow. In Ukraine it was first registered in 1988 in the Vishnia River (tributary of San), and was also found in the river Zolota Lipa (tributary of the Dnieper). Today spreading is unknown as a result of a lack of scientific information.

According to undocumented information Perciformes was found in the reservoirs of Ternopil Region (1997) and in Lviv Region (in particular in the nature reserve Rostochia). The expansion of its natural habitat is very undesirable; the species is very strong and will survive in spite of a difficult condition of natural abiotical factors (including freezing and lack of oxygen in the water). It spawns in the summer; the spawn is guarded. The grown-up individuals eat young individuals of various invertebrates. It is very insatiable, reaches an age of 5-7 years, and is not industrially important. Preudorasbora parva (Schlegel) is a small fish, that belongs to Cypriniformes. It originally comes from a basin of the river Amur.

The species was brought accidentally to a Karakum Channel and to some Central Asia reservoirs, and then, again accidentally found itself together with herbivorous fishes in the water bodies of Ukraine (was found first in the rivers Danube and Dnister, and than in the low-lying areas of Dnieper and Dnister) (1978). During the 1980s it was observed in reservoirs of the Dnieper cascade (beginning from the Kremenchug reservoir and lower).

At the beginning of the 1990s, a large number of the species was found in the reservoirs/precipitation tanks of Kiev WES-5 and the reservoirs near it. Its natural habitat is unknown because of a lack of scientific information. Young individuals eat plankton and adult individuals eat benton, but the part of plankton in the food is rather considerable. Its natural enemies in Ukraine are unknown as are its parasites.

Not long ago Lepotis gibbosus (L.) was brought to Europe by amateur aquariumists from North America. When it came to the Danube River it quickly entered the Black Sea and reached the Dnister River estuary. It has been found in the Odesa bay. Today the natural habitat of the species is unknown because of a lack of scientific information. It spawns in the coastal lakes of the Danube, and its spawn is guarded. It has no industrial importance, and is harmful to other fish species because it eats spawn and young individuals.

There could be other species of such fish, but due to a lack of scientific information (as a result of lack of scientific research) this question cannot be answered.

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