A review of historical and recent area of distribution of tubenose goby Proterorhinus marmoratus was undertaken using critical analysis of published literature, data from two large fish collections (Natural History Museum, Kiev, Ukraine, and Zoological Institute, St Petersburg, Russia), personal collections of the authors sampled during extensive field activities in 1998-2004, and unpublished reports of the Institute of Lake and River Fisheries in Volgograd. Historically, riverine P. marmoratus from the Black Sea-Azov basin were distributed in the upper reaches of the rivers Dnieper and the Don even before the construction of water retention structures; this form at present has demonstrated only limited upstream range expansion. The native ÔCaspian tubenose gobyÕ is mostly connected with sea and delta habitats. We adduce some arguments for the tubenose goby's recent invasion of the Middle and Upper Volga as a result of introductions of the Don-Azov riverine form rather than upstream dispersal of the Caspian marine form.

The parasitic fauna in the lower Volga River basin was investigated for four gobiid species: the nonindigenous monkey goby Neogobius fluviatilis (Pallas, 1814), the round goby N. melanostomus (Pallas, 1814), the Caspian bighead goby Ponticola gorlap (Iljin, 1949), and the tubenose goby Proterorhinus cf. semipellucidus (Kessler, 1877). In total, 19 species of goby parasites were identified, of which two - Bothriocephalus opsariichthydis Yamaguti, 1934 and Nicolla skrjabini (Iwanitzki, 1928) - appeared to have been introduced from other geographic regions. The monkey goby had significantly fewer parasitic species (6), but relatively high levels of infection, in comparison to the native species. Parasitism of the Caspian bighead goby, which is the only predatory fish among the studied gobies, differed from the others according to the results of discriminant analysis. The parasitic fauna of the tubenose goby more closely resembled those of Caspian Sea gobiids, rather than the Black Sea monkey goby.

Benthophilus durrelli and B. ragimovi, two new species of tadpole-gobies, are described. Both belong to an assemblage of Benthophilus species with clearly differentiated dermal ossifications. B. durrelli inhabits estuarine regions, deltas, lower reaches of rivers, and dam lakes in the Sea of Azov basin and is introduced in the Volga. It was hitherto not distinguished from the Azov tadpole-goby, B. stellatus, from which it differs in the posterior position of the second dorsal fin (behind vs. in front of the anal-fin origin), comparatively small (vs. considerable) difference in size of tubercles and granules, rectangular dermal fold with slightly undulated margin (vs. triangular, with clearly undulated margin), narrow (vs. wide) first semiring-like blotch behind the first dorsal fin, and 17-21, commonly 18-20 transverse rows of neuromasts on the flanks (vs. 20-25). B. ragimovi, a deepwater species, is only recorded at western coast of middle and south Caspian from Chechen’ Island to Astara. It differs from the closest congener, B. pinchuki, in the weak (vs. well-developed) depression on the head, absence of granules in the head depression, very small, densely-set granules located on whole upper head surface and anterior part of back, sometimes also on caudal peduncle (vs. enlarged granules located only along the lateral margins of the head depression), reduced first tubercles of the dorsal row (vs. anterior dorsal tubercles of the same size as the posterior ones).

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Data based on the results of published, unpublished, and questionable materials concerning the occurrence of anadromous sturgeons after damming of the Don River downstream and upstream of the Tsimlyansk hydroengineering complex are presented. Two peaks of approaches of spawners to the dam in the 1950s and 1980s were recorded. The first peak was related to the wild population that existed in these years; the second peak was a result of mass artificial propagation. At the first stage, the Russian sturgeon (Acipenser gueldenstaedtii Brandt et Ratzeburg, 1833) and the beluga sturgeon (Huso huso (Linnaeus, 1758)) prevailed downstream from the dam; at the second stage, only the Russian sturgeon was recorded. Since 1955, only 21 individuals of anadromous sturgeons have made it through the dam by a fish ladder. During the years 1952-1961, 1145 individuals were transported into the reservoir, including 218 ind. of beluga. Some individuals of beluga were transported later as well. There are data indicating the presence of juvenile beluga individuals that originated from natural spawning in the reservoir before the 1970s. The last known spawners of Russian sturgeon and stellate sturgeon (Acipenser stellatus Pallas, 1771) in the reservoir were recorded in the 1980s or 1990s. Solitary beluga individuals may occur nowadays. It is suggested that the youngest of the noted individuals belong to the generations of the early 1990s. It is concluded that the extremely innumerous landlocked form of the Azov beluga may still exist in the reservoir.