The occurrence of the Chinese sleeper Perccottus glenii Dybowski , 1877 in the Southern Bug River Basin , Ukraine

In 2013, 71 specimens of Perccottus glenii Dybowski, 1877 were caught in Ukraine in a tributary of the Southern Bug River, known as the Hirskyi Tikych. Present study confirms the expansion of this invasive species in Ukraine and also in Europe.


Introduction
The Chinese sleeper, Perccottus glenii Dybowski, 1877, is a representative of the Odontobutidae family (Acanthopterygii: Perciformes), which originated in freshwater rivers flowing into the Japanese, Okhotsk and Yellow seas, in the Far East, Asia (Mori 1936;Berg 1949).This fish was first introduced to European waterbodies following a release by aquarists.It is currently one of the most successful fish in European waterways (Reshetnikov 2010).The Chinese sleeper is a small fish with a short life cycle, feeding on a wide variety of invertebrates, tadpoles and fish throughout its life cycle.It has no fishery value and therefore considered an undesirable invasive species, with a significant non-native range in both Europe and Asia (Reshetnikov 2010).
In Ukraine, the Chinese sleeper occupies the basins of the Danube (including the Prut and Tisza basins), Dniester, Dnieper and Bug rivers (Movchan 1989;Korte et al. 1999;Sabodash et al. 2002;Movchan et al. 2003;Kosco et al. 2004;Kutsokon 2012;Kvach 2012).The Southern Bug River is one of the largest rivers in Ukraine (806 km); it is the largest river among the rivers flowing exclusively by the territory of Ukraine (Kravchuk 1993).Some data exists regarding the presence of this species in the upper reaches of the Southern Bug system, but site-specific references or geographical coordinates are lacking (Reshetnikov 2013).The purpose of this study was to verify and confirm the presence of P. glenii in the Southern Bug River Basin.

Material and methods
Fish fauna analyses were carried out in the Hirsky Tikych River, which is one of the left tributaries of the Southern Bug River.Sampling was located near the village of Buzivka, Central Ukraine (49°6′27.9″N30°5′55.78″E).The river was characterized by a muddy bottom, sometimes with vegetation including Ceratophyllum, Phragmites, Potamogeton and Typha.Fish were sampled by trawl (8 m long, 0.5 cm in cell diameter) in both the spring (24.05.2013) and autumn (05.11.2013) seasons; depth of field up to 1 m.
Morphological analysis was carried out on captured fish.Standard length (SL) of each fish was measured.Number of rays on dorsal (D 1 , D 2 ) and anal (A) fins, and the number of transverse rows of scales (Squ) were counted; sex and stage of sexual maturity were also determined.

Results
In total, 71 specimens of Chinese sleeper were caught in the Hirskyi Tikych River: 49 specimens were caught in May (38.3% of total catchment) and an additional 22 specimens in November (2.8 % of total catchment); SL=62.9±1.4 (47.8-81.4mm) (n=44) (Figure 1).Meristic features are presented in Table 1.Of the 33 dissected specimens among collected in May, 15 were female and 18 male, while the November sample had 9 females, 11 males and 2 juveniles.Male/female ratio was almost equal (1:1.2) for both seasons.
In May, male specimens were both less mature (stages II and III) and ready to spawn (stage IV).Most males were in the 3 rd stage of sexual maturity (61%), with the lesser part in the 2 nd and 4 th stages (33% and 6% respectively).Most of females had reached maturity Stage IV (87%).Some females (13%) had two well developed batches of eggs: one already realized (stage VI), the other almost ready to be emitted (stage IV).Stage IV individuals were observed among females (22 %) and males (9 %) in November.Other observed individuals of Chinese sleeper were in the following stages: females: Stage II (56 %), III (22 %); males: Stage I (36 %), Stage II (18 %) and III (36 %).
A further 8 fish species were captured in May, and 12 in November (Table 2).An invasive fish species, the stone morocco, Pseudorasbora parva (Temminck and Schlegel 1846) dominated the catchment in both seasons (27.3 % in May and 62.5% in November).The percentage of alien species (Perccottus glenii, Pseudorasbora parva, Carassius gibelio and Pungitius platygaster) was significant both in spring and autumn, 70.3% and 68.5% respectively.

Discussion
This research confirms the successful penetration of P. glenii into the river systems of the Black Sea basin, and also the expansion of its nonnative range in Ukraine and Europe.To date, there is no published data regarding the presence of P. glenii in the Southern Bug River.Limited data from the upper river system was presented  (Kutsokon 2010).The riverbed at the site of the study is also favorable to other alien species.The most numerous alien fish species was the stone morocco.The distribution of this species is also directly related to the location of aquaculture ponds (Karabanov et al. 2010).
Meristic features of P. glenii are largely similar to the statistical range of previously published data for Ukraine (Sokolov 2001; Table 1).The number of branched-rays were slightly greater in the anal fins and the number of lateral rows of scales were also higher.There may be some morphological variation of this species in Ukraine.Sampled fish generally measured between 50 to 80 mm (Figure 2).Specimens of Chinese sleeper sampled in November were ready for spawning.Perhaps this was caused by weather conditions, i.e. a cold September followed by a warm October.Since all specimens examined were sexually mature, the size-class can be considered as a basis for spawning.Data collected corresponds to the reproductive biology of the Chinese sleeper, namely portioned spawning and active care of offspring by the male.

Table 2 .
Percentage of fish species in the Hirskyi Tikych River, near Buzivka village, Ukraine (May and November 2013).