The ichthyofauna of the Moksha River , a tributary of the Volga river basin , Russia

The results of an 11-year study of the ichthyofauna in the Moksha River (central part of European Russia) are described here. Thirty-seven species were recorded, including 34 present in rivers and 26 in lake systems. Relative abundance and the occurrence of fish species from different types of water bodies are provided and the diversity of the ichthyofauna for this region is discussed.


Introduction
The Moksha River is one of the largest tributaries of the Oka River drainage, and the largest right-bank tributary of the Volga river basin.As a result, there is fragmentary information on the diversity of ichthyofauna in this basin.
Although this region of Russia is densely populated, the ichthyofauna of the Moksha River was not deeply studied by any recent long-term integrated research project.The first main studies about the fish diversity of the Moksha River were by Magnitskii (1928aMagnitskii ( , 1928b)), which recorded species from the Penza province and documented the differences between the ichthyofauna of Moksha and the adjacent Sura River.Posteriorly, a more detailed study in this same region was conducted by Dushin (1967Dushin ( , 1978)), in a period that saw a massive degradation in many Russian rivers caused by pollution.More recently, a great number of unconnected studies in local journals were published (Artaev et al. 2013, Kuznetsov and Barkin 2003, Lysenkov et al. 2010, Lysenkov and Pjanov 2015) with some level of information of fish diversity for this region, but they did not provide a complete scenario of fish abundance and distribution extension of the species in the Moksha river basin.The goals of this study were to assess the diversity, occurrence, distribution extension, and abundance of fish species in different types of water systems to the Moksha river basin.

Materials and Methods
Study site.The Moksha River is situated on the Russian plains between altitudes of 80 to 270 m.The river comprises about 656 km and drains an area of 51,000 km 2 .The Moksha River is a plain-type river.Precipitation in the drainage's southern area is approximately 475 mm per year but in the northern portion it can reach up to 500 mm (Yamashkin 1998).The monthly average runoff of ANNOTATED LIST OF SPECIES rivers in the Moksha drainage varies throughout the year.Low-water periods are in the summer/fall and winter periods, and 70% of the annual runoff is during the spring flood (Mil'kov 1981).Melting snow is the major source feeding the rivers in this region, while groundwater runoff accounts for about 24% and precipitation in the form of rain account for just 5%.The average air temperature of the warmest month (July) is 20 °C and of the coldest month (January), -12 °C.(Mil'kov 1981).
Data collection.A total of 34,716 individual were collected between 2004 to 2015, using seine net (6 m × 1.25 m, 6 mm between knots and 10 m × 1.25 m, 8 mm between knots, but 6 mm in the pocket), dip net (1 m × 1 m of frame; 1.5 m pocket length, 6 mm of mesh size), and stake gill nets (30 m × 1.5 m, 1.7, 3.0, and 5.0 cm between knots).Specimens were fixed in 10% formalin and preserved in 70% alcohol, and posteriorly identified using the identification keys of Kottelat and Freyhof (2007).Taxonomic nomenclature is following Eschmeyer (2017).Specimens were captured under the permits of Federal Fishery Agency No. 348 on extraction of aquatic biological resources YP No. 035786.Collected fishes were cataloged in the Ichthyological Collection of Mordovian State Nature Reserve.A list of species sampled in this study and its catalog number are listed in Table 1.The samples and the geographic coordinates of locations are provided in Table 2.
Data analysis.The habitats over the Moksha River and other water systems where the specimens were collected were categorized according to the physiognomy of the system and then classified into distinct groups according to the distance range of the sampling site from the source of the river 0-25 (Fig. 1A), 26-100 (Fig. 1B), 101-300 (Fig. 1C), and 301-500 km (Fig. 1D), which was calculated using freely available topographic maps at a scale of 1:200 000.The categorization of those water bodies that do not represent the category "rivers" in this study included flowing and landlocked oxbows, karst and suffusion lakes, ponds, and storage reservoirs (Fig. 2).Landlocked oxbows: lakes isolated from the river but periodically connected to it during spring floods; they vary from 0.2 to 45 ha in area and are from 2 to 10 m deep (Fig. 2A, B).Flowing oxbows: lakes permanently connected to the river either directly or via a tributary of the main river; these lakes are 0.9-17.4ha in area and 3-8 m deep (Fig. 2C).Karst and suffusion lakes: resulted from collapse or subsidence of the terrain; they are few in number and do not have a direct connection to the river;   -190, P-192, P-193, P-195, P-196, -197, P-198, P-199, P-200, P-201, P- -190, P-191, P-193, P-195, P-196, P-198, P-200, P-201, P-203
Reservoirs: over 1,000,000 m 3 (187-1090 ha; Fig. 2F).The occurrence of species was calculated as a × 100/b, where a is the number of water bodies where the species was recorded and b, the total number of examined water bodies.The mean shared in catch is the arithmetic mean for the relative sharing in catch calculated for the water bodies where a species was collected.

Results
The list of species, its abundance and distribution (Fig. 3) are briefly described below.The sympatric occurrence of species and rate occurrence in different water systems are shown in Table 3.

Material examined. Table 1.
Presence of a bicuspid endolateral tooth and spadelike caudal fin.This species was found in the southeastern portion of the Moksha River, which is the northeastern extent of the species' range.The Moksha River is one of the few tributaries of the Volga River drainage where this species inhabits (Artaev et al. 2013).During spring spawning, this lamprey is observed on almost all pebble shoals in the upper reaches of the Moksha River and its tributaries (Fig. 4).Material examined.Table 1; Fig. 5.
Presence of 56-71 lateral plates and first dorsal plate not fused to the head.It was not collected in this study, but was observed in the middle and upper reaches of the Moksha River on a regular basis (Kuznetsov et al. 2008, Lysenkov andPjanov 2015) (Fig. 5).Over the last decade, the abundance of this species has increased in the Moksha River, likely due to a regular release of the juveniles into the Oka River (Lysenkov et al. 2006).

Material examined. Table 1.
The only member of this family in European Russia; identified based on its long snout and large mouth.It is a widespread species in rivers and lakes but has been never recorded in karst and suffusion lakes.It is more fre-   quently observed in rivers (15.4-76.9%)than other water bodies; and most frequently at a distance over 100 km from the source.In non-river habitats, the species is more frequently found in landlocked oxbows (45.2%).
Presence of 23-30 branched anal-fin rays and 51-60 scales on lateral line.It was observed in all river types and other water bodies, except for ponds.It is rare in shallow rivers and its abundance is low; however, it is more common in larger rivers.Abramis brama is much more frequently found in floodplain lakes, flowing oxbows than in landlocked oxbows.It was found in reservoirs.Abramis brama is likely not native to the upper portions of the Moksha River, up to 25 km from the source, but rather it escaped from the constructed ponds in the upstream portions of the river.Berg, 1924 Material examined.Table 1; Fig. 6A.

Alburnoides rossicus
The only representative of this genus in the Volga River drainage (Bogutskaya and Coad 2009), identified by a small black spot on each side of lateral line pore and 12-17 branched anal-fin rays.Although included in the Russian Red List since 2001 (Danilov-Danilyan 2001), it is still rather abundant in the Moksha River (Ruchin et al. 2007(Ruchin et al. , 2009)).This species lives only in rivers, and its abundance in the Moksha drainage increases forward to downstream (12.8% in the river on a distance of 26 km from the source up to 38.5% in the river from 301 to 500 km from the source); more abundant (35.8%) in the portion between 26 and 100 km from the source of river.(Linnaeus, 1758)

, Bleak
Cyprinus alburnus Linnaeus 1758: 325.Alburnus alburnus- Kottelat and Freyhof 2007: 164.Material examined.Table 1; Fig. 7C.Presence of 45-48+3 lateral line scales; 17-20 branched anal-fin rays; and 16-22 gill rakers on first gill arch.It is an abundant species and is absent only in ponds; recorded in all sampled rivers at a distance of 26 to 500 km from the source.In upstream sections of rivers (up to 25 km from the source), its occurrence rate was 28.2%; in other water bodies, the rate varied from 16.1% in landlocked oxbows to 37.5% in flowing oxbows.The percentage of A. alburnus in catches increase with the size of the river, reaching 40% in sections of river between 200 and 500 km from the source.Its abundance in other water bodies is considerably smaller, about 1-9.1%.(Linnaeus, 1758), Zope.

Material examined. Table 1.
Presence of 33-34 branched anal-fin rays and upper position of the mouth.It is a rare species in the Moksha River (Fig. 4) and it was observed in the flowing oxbow lakes in the lower and middle portions of the river (12.5%), as well as in the middle and lower portion of the main river channel itself (7.7%).The share in catches is less than 1%.

Material examined. Table 1.
Presence of 32-42 branched anal-fin rays and by the sub-terminal mouth position.It has been recorded only in the middle and lower portions of the Moksha River (Fig. 4).Its presence in catches and occurrence rate increase with the river size but is still insignificant.(Linnaeus, 1758), White Bream.

Material examined. Table 1.
Presence of 19-23 branched anal-fin rays and subinferior mouth, which cannot be extended as a tube.The white bream has been observed in all types of water bodies, except in the smaller rivers (up to 25 km from the source) and the karst and suffusion lakes.The species reached the maximum occurrence 101-500 km from the source.In general, this species most frequently occurs in flow-through lakes and least frequently in ponds.(Linnaeus, 1758)

Material examined. Table 1.
Presence of a convex edge in dorsal fin and 23-33 gill rakers in first gill arch.This species avoids rivers, as well as is absent in the streaming oxbows connected to the rivers.This species is common in landlocked oxbows, karst and suffusion lakes, ponds, and storage reservoirs.It is most frequently found in storage reservoirs, which account for over 50%.The largest presence in the catch (65.4%) was recorded in karst and suffusion lakes.(Bloch, 1782)

Material examined. Table 1.
Presence of a concave border of dorsal fin and 37-52 gill rakers in first gill arch.This species used to be rarely captured in the 1960s (Dushin 1967), but is more frequently found nowadays, when compared to the congener C. carassius.The Prussian carp avoids large rivers (101-500 km from the source), as well as streaming oxbows.The occurrence in rivers farther than 100 km from the source is low, but abundant.The highest share in catches is recorded in landlocked oxbows and ponds; a high occurrence was observed in ponds and storage reservoirs.Yakovlev, 1870, Volga Undermouth.
Presence of an arched mouth and 50-62 scales on lateral line.It is a frequent species, but rather abundant and was recorded only in rivers 101-500 km from the source.Linnaeus, 1758, Common Carp.Cyprinus carpio Linnaeus 1758: 320-Kottelat and Freyhof 2007: 148.

Cyprinus carpio
Material examined.Table 1.Presence of two pairs of barbels and 15-20 branched dorsal-fin rays.According to our observations, it was found only in storage reservoirs; however, artificial stocking of this species in ponds is known, as well as rare cases when it is caught in the Moksha River and its oxbows.Vasil'eva, Mendel, Vasil'ev, Lusk & Lusková, 2008, Volga Gudgeon. Gobio volgensis-Mendel et al. 2008: 1073. Gobio gobio-Reshetnikov et al. 2003a: 250.Material examined.Table 1.Presence of two pairs of maxillary barbels, naked thorax between pectoral fins, and by the speckled dorsal and caudal fins.This species was recently recognized as valid, formerly considered junior synonym of G. gobio (Mendel et al. 2008), and inhabits rivers, ponds, and water reservoirs.In many shallow rivers, this species together Barbatula barbatula reach the upper streams.The share in catches decreases according to the increase in the river size.This species was rather common for rivers, accounting for over half of the cases in all types of rivers, and was rarely found and not abundant in landlocked oxbows.(Heckel, 1843), Belica.

Leucaspius delineatus
Squalius delineatus Heckel 1843: 1041.Leucaspius delineatus- Kottelat and Freyhof 2007: 203.Material examined.Table 1.Presence of an incomplete lateral line with eight to twelve pored scales, superior mouth position and keel covered by scales between pelvic origin and anus.The belica inhabit all types of rivers and water bodies, being most frequently found in landlocked oxbows and ponds, and it was somewhat less frequent in karst and suffusion lakes.The highest share in catches was observed in the same water body types and rivers up to 25 km from the source.Note that most ponds are formed in these small rivers and most likely the pond populations assist in maintaining a high abundance of this species in very small rivers.(Linnaeus, 1758)

Material examined. Table 1.
Presence of an elongate maxilla reaching beyond anterior margin of the eye, and a symphysis on the lower jaw.Leuciscus aspius was absent in the upper portions of rivers (0-25 km from the source) and attains the highest abundance in the river sections between 101-300 km from the source.This species was observed in the oxbows.The percentage in catches (2.3%) was observed in larger rivers (301-500 km from the source); in remaining cases, the occurrence was less than 1%.(Linnaeus, 1758), Ide.

Leuciscus idus
Cyprinus idus Linnaeus 1758: 324.more abundant and frequent in the latter.The rudd fish is most frequent in the streaming oxbows (75% of the examined water bodies), as well as landlocked oxbows and storage reservoirs (38.7 and 66.7%, respectively), and least frequent in the karst and suffusion lakes.This species was observed in all types of rivers, but it is not abundant and has a low share in catches (0.1-2.7%).Its occurrence rate gradually increases according to the river enlargement, from 2.5% at 25 km from the source, to 15.4-25% at 101-500 km from the river source.(Linnaeus, 1758) Material examined.Table 1; Fig. 7A.Presence of a convex border of anal fin, and by the orange to red color in the anal and pelvic fins.The chub inhabits all types of rivers and oxbows, and was absent in the karst and suffusion lakes, ponds, and storage reservoirs.This species was most frequently caught in rivers 26 to 500 km from the source, being the most abundant species (maximum share, 8.6%).The chub was more frequently found in flow-through lakes than in landlocked oxbows.(Linnaeus, 1758), Tench.

Tinca tinca
Cyprinus tinca Linnaeus 1758: 321.Tinca tinca- Kottelat and Freyhof 2007: 296.Material examined.Table 1.Green pattern color of body and presence of small scales.This species does not inhabit rivers and has been observed only in other types of water bodies, except for karst and suffusion lakes.It most frequently inhabits reservoirs (33.3%) and streaming oxbow lakes (12.5%), with a slightly rarer occurrence in ponds and landlocked oxbows (7.1 and 6.5%, respectively).Its share in catches in all types of habitats varies in the range 1.7-2.6%.
Cobitis barbatula Linnaeus 1758: 303.Barbatula barbatula- Kottelat and Freyhof 2007: 329.Material examined.Table 1.Presence of 15-16 branched caudal-fin rays and by the cylindrical body shape.It has been recorded in rivers of all types and river ponds.This is the most abundant species in shallow rivers, which inhabit the springhead of many rivers, frequently being the only representative of species of the fishes in such channel rivers.According to river enlargement, its occurrence rate and share in catches decrease, stabilizing at levels of 15.4-16.7 and 1.2-2.2%,respectively, 100 km from the river source.The stone loach abundance in ponds was low (0.4%), as well as its occurrence rate (3.6%).Nichols, 1925, Siberian Loach. Cobitis melanoleuca Nichols 1925: 3-Kottelat and Freyhof 2007: 309.Material examined.Table 1.

Cobitis melanoleuca
Long and laterally compressed body shape and presence of two black spots on the caudal-fin base.It has been observed in rivers up to 100 km from the source.Its occurrence rate is rather stable with river enlargement (37.7-41%), while the share in the catch decreases from 13.4 to 7.3%.This species was rather rare in other types of water bodies; it was recorded only in one pond, where its share in the catch was less than 1%.Linnaeus, 1758, Spined Loach.Cobitis taenia Linnaeus 1758: 303-Kottelat andFreyhof 2007: 314.Material examined.Table 1; Fig. 7D.Long and laterally compressed body shape; presence of one black spot on the caudal-fin base.This species is morphologically similar to the Siberian loach, which inhabits rivers and is uncommon in other types of water bodies (recorded in only one landlocked oxbow).Unlike the Siberian loach, C. taenia was observed in all types of rivers.The abundance in rivers varies in the range 0.9-5% and the occurrence rate in the range 23.1-54.7%.(Linnaeus, 1758), Weather Fish.

Misgurnus fossilis
Cobitis fossilis Linnaeus 1758: 303.Misgurnus fossilis- Kottelat and Freyhof 2007: 319.Material examined.Table 1.Presence of three pairs of barbels with four long barbel-like mental lobes and a cylindrical body shape.It was observed in muddy rivers to 25 km from the source and in oxbows.This species is most abundant and frequent in streaming oxbows.Linnaeus, 1758, Wels Catfish.Silurus glanis Linnaeus 1758: 304-Kottelat andFreyhof 2007: 340.Material examined.Table 1.Presence of two pairs of mental barbels and 83-91 total anal-fin rays.This is the sole species of the family Siluridae in the Volga river drainage.According to our observations, it inhabits only rivers to 25 km from the source.Its abundance increased with river enlargement from 0.6 to 5.9%, and its occurrence rate from 3.8 to 15.4%.
Gadus lota Linnaeus 1758: 255.Lota lota- Kottelat and Freyhof 2007: 462.Material examined.Table 1.Presence of only one mental barbel, centralized, and pelvic origin anterior to pectoral-fin origin.It was recorded only in rivers; its share of the catch varies from 1.5 to 4.2%, and occurrence rate from 7.7 to 18.9%.

Family Percidae
Gymnocephalus cernua (Linnaeus, 1758)  24-27% SL.This species inhabits different size rivers, oxbows, and storage reservoirs, most frequently in rivers 101-300 km from the source (47.7%) and storage reservoirs (66.7%).In the latter, this species was most abundant in catches (19.1%).Linnaeus, 1758, European Perch.Perca fluviatilis Linnaeus 1758: 289- Kottelat and Freyhof 2007: 530 Material examined.Table 1 Presence of dark blotch on posterior portion of dorsal fin, and five to eight bold dark bars on flank.It is a wide-spread species, which was recorded in all types of water bodies.In rivers, this species is most frequent 100 km from the source and in other water bodies, in streaming oxbow lakes.Its share in river catches is low and varies from 2.8 to 9.7%, being approximately the same for the flow-through lakes.Such as for the remaining water bodies, its share in catches is higher, amounting to 12.8-31.4%,with a maximum in ponds.(Linnaeus, 1758), Pike-perch.Presence of two dorsal fins without spines, first and second dorsal fin with six to eight unbranched rays, and second dorsal fin with eight to 12 branched rays.This is an invasive species, first found in 1979 (Potapov et al. 1998).It was recorded in small rivers (to 101 km from the source) and all other types of waterbodies, except for storage reservoirs.Its highest occurrence rate was observed in oxbows as well as karst and suffusion lakes (75-87.6%).Its occurrence rate in ponds is moderate (28.6%), and in rivers, low (10.3%;rivers to 25 km from their source); or very low (1.9%; rivers at 26-100 km from their source).The highest abundance was observed in landlocked oxbows, where its average share in catches is 30.9%.Gratzianov 1907, Volga  Material examined.Fig. 6D.Presence of 1 lower jaw pore, and incomplete lateral line usually with 17-25 pores.This is the only species of the genus Cottus in the Volga river drainage.It is a rare species, inhabiting only rivers system.Five localities are known to the distribution of this species and are shown in Fig. 4 (Artaev and Ruchin 2015), one of them (Fig. 4, easternmost point) housing a stable population; the remaining cases represent solitary catches.

Discussion
Moksha River drainage is inhabited by 37 species of fish herein recorded, in which 34 of them recorded in river ecosystems and 26 in lake habitats.
The stream volume had a rather insignificant effect on the number of species observed in the examined group of rivers.The number of species in catches increases according to the enlargement of the river, reaching a plateau of 10-11 species in the river sections over 100 km from the source.The occurrence rates of Abramis brama, Blicca bjoerkna, Squalius cephalus, and Silurus glanis showed a distinct trend of an increase with the stream size (distance from the source); Barbatula barbatula showed a distinct opposite trend (decrease in occurrence rate with distance from the source).Some species, such as Acipenser ruthenus, Ballerus sapa and Chondrostoma variabile, occur in larger rivers, whereas others such as Rhynchocypris percnurus, Carassius gibelio, Perccottus glenii, Misgurnus fossilis and Cobitis melanoleuca are absent in larger streams.The first four species do not inhabit larger rivers, they are limnophilic species.The presence of limnophilic species in small rivers could be most likely explained by the fish escaping from ponds in small streams.Most species showed an increase in occurrence rate with the enlargement of the river and its stabilization occurs at a distance exceeding 100 km from the source.
The richest species composition among the remaining examined groups of water bodies was found in landlocked oxbows, including 21 species, and the poorest were found in karst and suffusion lakes (11 species).In general, the largest number of species was recorded in the oxbows, which can be explained by their tight association with the river floodplain formed during the spring floods.A comparison of landlocked and streaming oxbows showed that the former has a larger number of species.Presumably, this is determined by more diverse conditions in the landlocked oxbows, including different areas, depths, association with an open or a closed part of the floodplain, as well as different oxygen regimes, which change depending on the presence of underwater springs.An average of 6.5 species is present in one catch from streaming oxbows versus 5.3 species in landlocked oxbows.Presumably, this difference is explainable by the group of landlocked oxbows including small water bodies, subject to suffocation, which contain only two species each.The karst and suffusion lakes originated and are located independently of the river network, allowing fish migration; most of these water bodies are isolated from rivers, determining their poor ichthyofauna (12 species).Ponds and storage reservoirs are artificial water bodies formed by damming of a stream; they differ in the size of the dammed water flow: ponds are formed on shallow rivers and brooks, storage reservoirs on larger rivers.Despite this difference, the number of species living there is equal; however, three species on the average were present in one pond locality versus ten species in storage reservoirs.A larger number of species in each storage reservoir could be explained by their ichthyofauna being formed by larger rivers, which is richer in species composition and in some cases, additionally by floodplain water bodies, as well as their larger sizes, resulting in a higher diversity in biotopes.
The following species can be regarded as rare for the Moksha River drainage: Acipenser ruthenus, Cyprinus carpio, Pelecus cultratus, Sander volgensis, and Cottus gobio.Perccottus glenii (recorded for the first time in 1979) and Rhynchocypris percnurus (recorded for the first time in 1978) are invasive species in this river basin (Potapov et al. 1998).
This was the first study to comprehensively analyzing the ichthyofauna of Moksha river basin, and the results of this study revealed two species previously unreported for Moksha river, Romanogobio albipinnatus and Cobitis melanoleuca, in which previous studies could not differentiate it from closest related species (Dushin 1967(Dushin , 1978)).In our study we could not capture Acipenser ruthenus although we had evidences in the Moksha river by fishermen's catches data and underwater pictures divers (Fig. 5); and Sander volgensis was only recorded from literature (Lysenkov et al. 2010).

Figure 1 .
Figure 1.Sampling sites.A. Skachki River, locality classified at a distance of 25 km from the source river.B. Aza River, locality classified at a distance of 26-100 km from the source river.C. Middle reach of Moksha River, locality classified at a distance of 101-300 km from the source river.D. Lower reach of Moksha River, locality classified at a distance of 301-500 km from the source river.

Figure 2 .
Figure 2. Reservoirs sites.A. Large landlocked oxbow in the floodplain Atmis River.B. Lake Vertyachka, small landlocked oxbow in the floodplain Moksha River.C. Lake Mordovskoe, streaming oxbow in the floodplain Moksha River.D. Lake Morskoy Glaz at karst origin.E. Pond in Tambov oblast.F. Vadinskoe storage reservoir, view from the plane to a height of 5 km.

Figure 3 .
Figure 3. Map of sampled sites, middle European part of Russia, Moksha river basin.

Figure 4 .
Figure 4. Map of occurrence of rare and restricted species, middle European part of Russia, Moksha river basin.

Figure 5 .
Figure 5. Shoal of Acipenser ruthenus in the Moksha River at a depth of 10 m.Photo by diver I. Sibgatullin.

Table 1 .
List of species examined in this study and the correspondent cataloged number of vouchers at the Ichthyological collection of Mordovian state reserve.

Table 2 .
Geographic coordinates of the sampling fishes cataloged at Ichthyological Collection of Mordovian State Reserve.

Table 3 .
Share in catch and occurrence rate in different groups of water systems.Sh= share in catch; Oc= occurrence rate; and (+) = literature data.* Abundance of the Ukrainian brook lamprey was not surveyed.

the indicated distances from the source, km Streaming oxbows
, Russian Schneider.

Table 1 .
, Ruffe.Presence of two confluent dorsal fins, and body depth Material examined.

Table 1 ;
Table 1 Presence of spindle-shaped body, canine teeth in the anterior portion of each jaw, and 80-97 scales on lateral line.It was observed in large rivers 100 km from the source (Ivanchev and Ivancheva 2010).Its occurrence rate is 8.3% and the share in catches is low.Perccottus glenii Dybowski 1877: 28-Kottelat and Freyhof 2007: 549.Fig. 6C. Sculpin.