Neogobius melanostomus, (Pallas)

Taxonomic description of species

Appearance typical of gobies. Body elongate, covered with scales, posterior portion slightly compressed laterally. Sensitive canals and pores present. Nape, top of head, neck, belly, and pectoral peduncle covered with scales. No barbels. No swim bladder. First dorsal fin rays 6-7, second dorsal with 12-17 rays. Color: body light brown or gray with dark spots on sides. Differs from other Neogobius sp. with shorter head and presence of bright black spot on posterior part of first dorsal fin. Spawning males are black overall.
Intraspecific forms. Caspian populations were formerly considered as subspecies. Division into subspecies is not accepted in contemporary studies (Miller, 1986; Vasilyeva, 1998).
Related forms. Related forms of round goby inhabit the Black, Azov, and Caspian Sea basins:
Neogobius bathybius (Kessler, 1817)
N. caspius (Eichwald, 1831)
N. eurycephalus (Kessler, 1874)
N. fluviatilis (Pallas, 1814)
N. gymnotrachelus (Kessler, 1857)
N. iljini Vasiljeva et Vasiljev, 1996
N. platyrostris (Pallas, 1814)
N. ratan (Nordmann, 1840)
N. rhodioni Vasiljeva et Vasiljev, 1994
N. syrman (Nordmann, 1840)

Distribution of species within the Caspian Sea

Distributed throughout the Caspian. In the North Caspian the biggest concentrations are recorded at the outlet of eastern branches of the Volga river, areas of Kulaly Island and Chistaya banka; the eastern part of the North Caspian is less occupied (Stepanova, 1983). In the Middle and South Caspian this species inhabits shallow zones of western and eastern coasts; it is the most abundant and widely distributed species among gobies (Ragimov, 1976).
Status as per International Red Data Book. IUCN Red List, 1996: DD
Status as per National Red Data Books: N/A
First record for the Caspian: Eichwald, 1831
Redescription of species: Gaibova, 1952; Ragimov, 1967; Vasilyeva, 1998

General characteristics of species

Ecologo-taxonomic group. The species may be equally referred both to nekton and macrozoobenthos. The most pelagic species as compared with other gobies.
Origin. Refers to Ponto-Caspian zoogeographic group. Ponto-Caspian endemic.
World distribution covers coastal zones of the Black and Caspian Seas, the whole area of the Azov Sea, lower reaches of the rivers flowing into them, as well as the Sea of Marmora. In late 1950-s, round goby was accidentally introduced into the Aral Sea in the course of introduction of mullet from the Caspian Sea (Konovalov, 1959; Markova, 1962; Miller, 1986). Round goby successfully invaded Kuibyshevskiy reservoir and was found in the Middle Volga and Moskva River (Gavlena, 1970; Sokolov et al., 1994), its abundance increases there.
Habitat. Occurs at shell/sand and silt beds, prefers shells and stony grounds (Ragimov, 1968, Stepanova, 1983); can be found among thick vegetation (Ilyin, 1949).
Migrations. Spawning and feeding areas are located adjacently (Ilyin, 1949). In winter migrates to deeper sea areas (up to 150-200 m), in spring and summer feeds at depth 0.5-15 m.

Relation to abiotic environmental factors

Relation to salinity. Euryhaline species. Marine fish, penetration into fresh water bodies had derivative character. Found in Kaidak and Mertvyi Kultuk bays at salinity 20.0-36.9� (Khaldinova, 1951).
Relation to temperature. Eurythermic species. The water temperature at habitats varies from -1^oC to +30^oC, though the fish is less active at temperature below +6^oC (Ilyin, 1949).
Vertical distribution. Euribathic species. Occur at sea depths 5-10 m; during spawning might be found at 0.2-0.5 m depth. By winter it moves to depths of 60-70 m, single individuals were found at 150-200 m.
Relation to oxygen conditions. Dwells at the bottom where oxygen deficiency occurs more frequently. Threshold oxygen concentration varies from 0.3 to 0.9 mg*l^-1 depending on weight of fish.
Relation to fluctuations of the sea level. During the period of the sea level rise (1978-1995), as a result of desalination the abundance of round goby in the North Caspian declined 3-fold, its habitat area decreased as well. Feeding on crustaceans reduced, cannibalism was recorded (Stepanova, 1994, 1996).

Feeding

Feeding type. Heterotrophic
Feeding behavior. For feeding on sedentary and inactive animals round goby features a variety of morphological adaptations in oral, maxillomandibular and pharyngeal structures (Bogachik, 1967). Pharyngeal apparatus of crushing type enables consuming mollusks; specialized maxillomandibular apparatus facilitates feeding on sedentary forms of Mytilaster, Dreissena, and Balanus.
Food spectrum. Crustaceans, worms, mollusks, as well as vegetation and larval insects. Importance of benthic organisms rises in diet of larger fish, feeding on plankton decreases (Gaibova, 1952, Stepanova, 1996).
Food supply. Higher Crustaceans (amhipods, mysids, crabs), mollusks (Dreissena, Mytilaster, Abra, Didacna, Monodacna), and worms hold much significance in food supply of the species.

Feeding habits of round goby in the North Caspian
(T.G. Stepanova, unpublished data)

In the North Caspian feeding on Crustaceans decreased concurrently with increased importance of mollusks in late years (Stepanova, 1996). At the western coast of the Middle Caspian round goby feeds on mollusks (48.2-85.8%) and crustaceans (15.0-32.7%). In the South Caspian the most significant are crustaceans (50-60%) followed by fish (30-35%) and Nereis (20-25%) (Gaibova, Ragimov, 1979).

Reproduction

Reproduction type. Sexual
Reproduction areas. Spawns both in fresh and saline water (Khaldinova, 1951, Koblitskaya, 1981). Spawning areas are situated in the coastal area at depth 0.5-8.0 m. Females deposit eggs on various solid substrate (stones and deserted shells of mollusks) and underwater objects (wood, iron, etc.).
Terms of reproduction. In the northern part of the Caspian Sea spawning lasts from April-May till August-September; at the western coast of the South Caspian - from early March till September-October (Ragimov, 1968; Stepanova, 2001). Batch spawning, up to 6 batches per spawning season.
Fecundity. Fecundity varies in wide range from 314 to 3744 eggs.

Limiting factors. The main reasons for eggs mortality are: oxygen deficiency, pollution of coastal areas with oil products, and tides, which completely dry sizeable spawning areas. If male does not protect deposited eggs, they are eaten completely by crustaceans in 2-3 hours.

Life history and development

Life-history stages. Hatching occurs on the 14th - 20th day; newly hatched gobies possess well developed/ definitive organs of locomotion, vision, digestion, respiration, though comparatively big yolk sac is present (Moskalkova, 1967, 1978; Dmitrieva, 1968). Gobies related to genus Neogobius feature shorter larval development (absence of pelagic stage). TL at hatching is 5.0-5.5 mm, in July-August fry is 40-60 mm TL, by September fingerlings reach 70 mm (Koblitskaya, 1981). Juveniles inhabit benthopelagic water layer. Underyearlings are 25 - 69 mm TL (Stepanova, 2001).
Relation to environmental factors. N/A
Age of maturity. Females mature at the age of 2 years, males - at the age of 3 years (Savvaitova, 1959). In the North Caspian gobies mature more rapidly (at 3.0 - 3.4 cm TL) than in the Middle Caspian (4.5-6.0 cm TL)
Thermal conditions of development. Incubation occurs at water temperature 18-27^oC and lasts 17 and 9 days, respective to the lower and upper thermal limit, at still lower temperature embryonic development takes 21 day (Dmitrieva, 1968).
Quantitative characteristics of growth. Age-related changes in length and weight are described by Shmalgauzen growth equation (1935):
L = 49.2 t^0.322; W = 2.8518 t^1.099; where
L - total length, mm
W - weight, g
t - age, years
In the course of the first year of life, males and females are almost equal in size. Starting from the second year, growth rate of males is higher than in females. After the 1st spawning growth rate is retarded (Stepanova, 2001).

Structural and functional population characteristics

Sexual structure. In June and August, males prevail over females in number, in September sex ratio changes in favor of females. It is probably attributed to the fact that the major part of males dies, and recruitment of newly mature individuals does not replenish the losses.

Sexual structure of round goby, North Caspian population, in 1984, %

Age-size structure. Mean age of the North Caspian population - 2 years old, maximum age - 4 years old, mean TL - 51.5 mm, maximum age - 4.2 years old, minimum size - 5.0 mm, maximum size - 90 mm (Stepanova, 2001). 
Males are bigger in size than females. Mean length of males of the same age group is 59.4 mm, in females - 52.8 mm. In the Middle and South Caspian the maximum age is 5-6 years (Ragimov, 1976).

Size and sexual composition of round goby  population in the North Caspian in August, 1984 (%)
(data provided by T.G. Stepanova)

Quantitative characteristics. In 2000, abundance of the species in the North Caspian amounted to 309.37 million individuals, stock reserve - 1.58 thousand tons. Compared with corresponding data for the year 1974, the abundance decreased 2.6 times (821.73 million individuals), biomass decreased 1.9 times (2.96 thousand tons) (Stepanova, 1996).
Population trends. Population abundance tends to decrease.

Interspecific relations

Round goby as a benthophagous species competes with other gobies, cyprinids (specifically, roach), and sturgeons. Rate of food affinity calculated upon species composition of food items (Shorygin, 1952), was the highest when compared with the other gobies - Neogobius fluviatilis, Hyrcanogobius bergi, and N. gymnotrachelus. Food affinity was attributed mainly to consumed crustaceans. Gobies are important food item of sturgeons, shads, inconnu, asp, zander, catfish, and seal. Gobies contribute to 80% of total food weight in adult Russian sturgeon and beluga (Polyaninova, 1985), up to 40% in winter and summer diets of seal.

Importance of species to bioresources production of the Caspian Sea

Economic significance of species. Round goby has certain importance in anglers fishing at city areas of Makhach-Kala, Derbent, Baku, Bautino, Aktau, Bektash, Turkmenbashi, etc.
Commercial characteristics of species, catches. No commercial importance
Fishing gears and fishing zones. None

Impact of fisheries on the population status

Gobies come as bycatch in shad harvests at the western coast of the middle Caspian, though their number is not assessed/ registered.
Human impact/Threats. Considering inactive behavior pattern of the species and specific ways of oil contamination, hydrocarbon pollution will cause the most significant damage to the population.
Conservation measures. Exploitation of artificial spawning grounds at shallow areas of the Caspian Sea and its bays is proposed as conservation measure for Gobiidae stocks

References

Bogachik, T.A. 1967. Morphological adaptation of the mylo-pharyngeal aparatus of gobies Gobiidae. J. Voprosy Ukhtiologii (Problems of Ichthyology). Vol. 7, 1(42): 108-115.
Caspian Sea: Fauna and biological productivity. 1958. Gobies nutrition. Nauka, Moscow pp. 214-220.
Gaibova, R.A. 1952. Gobies of Shikhovo-Karadag area of the Caspian Sea. Proceedings of the Institute of Zoology of Azerbaijan SSR AS. Vol 15, pp. 53-106.
Gaibova, R.A. and D.B. Ragimov, 1979. On the problem of goby feeding at the western coast of the Middle and Southern Caspian. News of Azerbaijan SSR AS. Series of Biological Science. 4: 58-64.
Gavlena, F.K. 1970. Caspian goby Neogobius melanostomus affinis Eichwald as a new element of the ichthyofauna of the middle Volga River. Bulletin of the In-land Waters. 6: 44-45.
Dmitrieva, E.N. 1968. Morpho-ecological analysis of Neogobius fluviatilis (Pallas) development at the embryo stage. Morpho-ecological studies of fish development. Nauka Press. Moscow. pp. 90-113.
Eichwald, E. 1831. Ecologia Zoologia specialis. p. 76.
Ilyin, B.S. 1949. Gobies. Atlas: Commercial fish species of the USSR. Pisshchepromizdat. Moscow pp. 642-644.
Khaldinova, N.A. 1951. Data on reproduction and development of fish in salty bays of the Northern Caspian. VNIRO Proceedings. Vol. 18, pp.99-120.
Koblitzkaya, A.F. 1981. Inventory on freshwater fish juveniles. Moscow. pp. 178-183.
Miller, P.J. 1986. Gobiidae in FNAM. Paris. UNESCO. Vd.3. pp. 1019-1085.
Moskalkova, K.I. 1967. Ecological-morphological characteristics of round goby (Neogobius melanostomus) development. In: Morphological analysis of fish development. Nauka Press. pp. 95-119.
Moskalkova, K.I. 1978. Development of Azov round goby Neogobius melanostomus (Pallas) in view of specifications of its existence in individual and historical development. Ecological-morphological and ecological-physiological investigations of fish development. Nauka Press. Moscow pp.72-88.
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Ragimov, D.B. 1976. Materials on distribution and abundance of gobies at the western coast of Middle and Southern Caspian. News of the Azerbaijan SSR AS. Series of Biological Sciences, 2: 83-88
Savvaitova, K.A. 1959. Some problems of the biology of non-valued fish in the lower part of the Volga River delta. Research Reports of Higher School. Biological Science, 2: 22-37.
Shorygin, A.A. 1952. Feeding and nutritional interrelations of fish in the Caspian Sea. Pishchepromizdat. Moscow. 268 p.
Skazkina, E.P. 1964. Some characteristics of round goby respiration. Proceedings of the Azov-Black Sea Research Institute of Fisheries and Oceanography. 22: 125-131.
Sokolov, L.I., E.L. Sokolov and V.A. Pegasov, 1994. Ichthyofauna of the Moscow River within the precincts of the city and some data on its state. J. Voprosy Ikhtiologii (Problems of Ichthyology). Vol. 34, 5: 364-641. 
Stepanova, T.G. 1983. Abundance, distribution and nutrition of gobies in the Northern Caspian In: Complex utilization of the biological resources of the Caspian and Azov Seas. Moscow pp. 279-280.
Stepanova, T.G. 1996. Gobies under the conditions of rising level of the Caspian Sea. In: Proceedings of the 7th Conference of the RAS Hydrobiological Society. Vol.152-154. Kazan. 
Stepanova, T.G. 2001. Some features of reproduction and growth of gobies in the Northern Caspian. In: Ecology of young fish and problems of Caspian fish reproduction. VNIRO Press pp. 268-276.
Shmalgauzen, I.I. 1935. Definition of basic terms and methods of animals growth determination. Moscow pp. 8-60. 
Shulman, G.E., E.P. Vengrzhin, B.N. Dubinina, 1957. Characteristicsof gas exchane in gobies (Neogobius melanostomus and N. gyrman)of the Sea of Azov in view of their habitat conditions. J. Voprosy Ikhtiologii (Problems of Ichthyology), 8: 77-80.
Vasilieva, E.D. 1998. The family Gobiidae. In: Annotated catalogue of Cyclostomata and fish of Russian continental waters. Nauka. Moscow. pp.125-145.

Compiled by:

Stepanova T.G., CaspNIRKh, Astrakhan, Russia
Ragimov D.B., Institute of Zoology Azerbaijani AS, Baku
Mitrofanov I.V., Kazakhstan AS Institute of Zoology, Alma-Aty