Abramis brama orientalis, Berg

Taxonomic description of subspecies

Breams of the Caspian Sea populations are referred to the eastern subspecies. They are similar in their meristic features.
Abramis brama orientalis (the Volga River delta): D III 8-10, more frequently 9, A III 22-28, 25.2 on average. Lateral line scales 48-58, 52.2 on average, gill rakers on the first gill arch 20-27, 24.1 on average, vertebrae 42-45 (43.3 on average). Pharyngeal teeth formula: 5-5, less frequently 5-4. Antedorsal length - 56.3% of body length (TL), postdorsal length - 35.5% of TL. Maximum body depth - 35.8, minimum - 9.8. Snout length - 6.5, eye diameter - 4.8, head length - 21.6, head depth at nape - 18.9. Forehead width - 8.4, caudal peduncle length - 14.5 (Sidorova, 1980).
Intraspecific forms. According to L.S. Berg (1949), distinctions between the typical subspecies Abramis brama brama occurring in the basin of the North, Baltic, Black and White Seas and the subspecies Abramis brama orientalis inhabiting the basin of the Caspian and Aral Seas consist in the number of gill rakers on the first arch, vertebrae and scales in the lateral line.
Related forms. Abramis sapa (Pallas, 1814), or white-eyed bream, is dispersed in fresh waters of Europe, in the basins of the North, Baltic, Black Azov and Caspian Seas. Abramis ballerus (Linnaeus, 1758), or blue bream, is distributed in Europe from the Rhine to Ural River (Bogutskaya, 1998).

Distribution of subspecies within the Caspian Sea

Abramis brama orientalis inhabits the lower reaches of the Volga and Ural Rivers, North Caspian and Kizlyar Bay. It is distributed in the Kura River basin from Mingechaur reservoir to all additional water bodies. The species also occurs in the Divichin firth and Kumbashinka River.
Status as per International Red Data Book: N/A
Status as per National Red Data Books: N/A
First record for the Caspian Sea: Abramis brama Kessler, 1872
Redescription of subspecies: Markun, 1929; Grib and Vernidub, 1935; Shaposhnikova, 1948; Berg, 1949; Kozhara, Izyumov, 1991.

General characteristics of subspecies

Ecological-taxonomic group. Nekton
Origin. Autochthonous species of freshwater origin, Ponto-Caspian faunistic complex.
World distribution. Abramis brama orientalis inhabits the basins of the Caspian and Aral Seas.
Habitat. Benthic fish
Abramis brama orientalis inhabits three types of water bodies during its life span: rivers, delta-front of the Volga River, shallow areas of the Caspian Sea. It spawns at the low floodplains during spring flood season; feeds in the delta-front and sea. The most abundant are populations in the Volga and Ural Rivers. Freshwater forms exist as well.
Migrations. Abramis brama orientalis is a semi-anadromous fish, characteristic migrations are: spawning, feeding and wintering.
The Volga bream hibernates in the lower part of the delta and in the delta-front, in shallow water areas of the sea. In spring young fish migrate into the North Caspian, where the richest feeding grounds are located; mature specimens migrate into the rivers for spawning. The peak run of spawners takes place through the second half of April - first ten days of May at water temperature 8-12⁰C. Post-spawners make downward migration to the sea and the fore-delta, where they feed through summer and autumn. In September they move ashore (autumn migration); bream densities in the sea decrease gradually. By late October its run becomes less active.
The peak run into the Kura River is recorded in December and January. Bream migration into the Kumbashinka River occurs in March-April at water temperature 6.4-21.6⁰C.

Relation to abiotic environmental factors

Relation to salinity. Brackishwater euryhaline subspecies.
The Volga bream occurs at feeding grounds of water salinity up to 14�. Distribution of fish in the North Caspian is restricted by the isohaline curve 8� (upper limit of favorable salinity). The highest densities in all parts of the sea are recorded in zones with low salinity, 2-4� (Tanasiychuk, 1959; Sidorova, 1971). Spawns in fresh water (up to 2�).
Relation to temperature. Eurythermic species.
Abramis brama orientalis inhabits the zones with water temperature varying from 0.1 to 28⁰C. During the summer-autumn period, bream feeds actively in the North Caspian at water temperature up to 28⁰C. At the temperature above 28⁰C its growth rate decreases. The lethal temperature is 33-34⁰C (Alabaster, Lloyd, 1984). The spawning migration into the Volga River begins at water temperature 2-4⁰C, mass migration occurs at 8-12⁰C. It spawns at water temperature 8-25⁰C while the peak spawning occurs at 11-19⁰C.
Vertical distribution. Bottom fish, occurs at depths up to 9 m. Most young and adult fish keep at a depth of 4-5 m; in the Volga River delta-front - at depth 1-3 m.

Relation to oxygen conditions. Oriental bream is referred to the group tolerant to comparatively low oxygen content in water. Optimum oxygen concentrations, at which bream develops more successfully and the loss of embryos is the least, varies from 10 to 17.6 mg O₂/l (Zhukinsky, 1981). When oxygen concentration decreases to 3-5 mg/l, severe morpho-functional alterations lead to the total mortality of embryos.
Relation to fluctuations of the sea level. A drop in sea water level by 2 m in mid-1970-s caused degradation of hydrological and hydrochemical conditions in the North Caspian. The area of low-salinity zones (up to 6�) was reduced. The food supply of (low-)brackishwater complex decreased; feeding areas sustained mostly in the western parts of the sea. These changes resulted in a considerable decline in the population of the North Caspian bream.

Feeding

Feeding type. Heterotrophic euryphagous (benthophagous) fish 
Feeding behavior. The mouth is subterminate, when wholly open looks like a very long proboscis directed downward at a certain angle to the longitudinal axis of the body. Operculum and its muscles are well developed, which is indicative of a powerful sucking ability of the mouth. In adult fish, pharyngeal teeth on the last gill arch grind the food.
Food spectrum. The diet of Abramis brama orientalis consists of mollusks, crustaceans, worms, Chironomidae, plants, sediment, insects. Since 1973, its feeding ration includes crab. 
Food supply. In 1990-s, biomass of main food organisms (Cumacea, Ampharetidae, Oligochaeta, Chironomidae) for bream in the North Caspian amounted to 17.6 g/m². During 1997-1999, biomass of food organisms was 6.1g/m².

Changes in biomass of the most important food items of oriental bream (g/m²)

Quantitative characteristics of feeding. The annual diet of oriental bream exceeds 11.5% of fish weight (Shorygin, 1952).

Reproduction

Reproduction type. Gamogenesis
Abramis brama orientalis is referred to phytophilic fish. Eggs are deposited on aquatic plants as well as on drifting remains of aquatic vegetation. Due to their adhesive membrane, eggs stick to plants. 
Reproduction areas. The major spawning sites of Abramis brama orientalis are located in the lower zone of the Volga River delta. Typical spawning sites are temporarily flooded water bodies, low- floodplains and lakes. River channels are second in importance. Spawning in the Ural River takes place at river banks.
Abramis brama orientalis in Azerbaijan spawns in supplementary water bodies located in the lower reaches of the Kura River, the system of Saryssu, Adzhikabul Lakes, the Kizlyar Bay.
Terms of reproduction. Spawning begins in early May coincident with spring flood. Mass spawning occurs in mid-May; spawning temperatures vary within 8-25⁰C. Spawning in Azerbaijan in Saryssu lakes starts in the third ten-day period of April, in the Kumbashinka River system - in May and June. Abramis brama orientalis spawns every year. During its life cycle, it can spawn 8-9 times.
Fecundity. Absolute individual fecundity of fish aged 3-11 years varies from 317,000 to 503,700 eggs. Average fecundity is 120,000-130,000 eggs. Fecundity increases correspondent to increase in length, weight and age of fish. Relative fecundity varies from 139 to 401 eggs per 1 g body weight (internal organs excluded), from 116 to 327 eggs per 1 g of total body weight.
Limiting factors

• Temperature regime at spawning sites:
  most eggs perish at a temperature below 6⁰C (Tanasiychuk et al., 1954). The rise in temperature up to 25.6⁰C results in early hatching of undeveloped prelarvae.
• Oxygen regime: optimal oxygen concentration is within 10-17.6 mg O₂/l (Zhukinsky, 1981).
• Sufficient food supply during transition of larvae to exogenous feeding and feeding of young fish at low floodplains.
• Larval survival is restricted greatly by predation.

Life history and development

Life history stages:

1. Embryonic - lasts 145-150 hours in natural conditions (Kononov, 1941).
2. Prelarvae - during the first six days they exist due to yolk sack storage, TL - 5-7 mm.
3. Larvae � transfer to exogenous feeding. The larval period lasts 17-20 days.
4. Juveniles - immature period - fry reaching the length of 20-25 mm migrate downstream into the sea. In September-October, they reach 70-75 mm TL. During the second year of their life cycle, development of gonads begins but fish is not able to reproduce yet.
5. Adult period - oriental bream starts spawning in the third year of its life cycle.
6. Senile period - the sexual function ceases in the 13-th year of life.

Relation to environmental factors. Maximum mortality is recorded at the early stages of development. The main contributing factors are: abrupt fluctuations and fall of water temperature during embryogenesis, unfavorable oxygen conditions, food deficiency during initiation of active feeding, predation by fish.
Age of maturity. Insignificant part of population matures at the age of two years (at 18-19 cm TL), some 40% - in the third year (24.5 cm TL), mass maturation (73.6%) occurs at the age of 4 years (27.7 cm TL). Males mature earlier than females
Thermal conditions of development. Optimum water temperature for developing eggs in the Volga River delta is 16.0-20.0⁰C; larvae develop at water temperature 16.0-25.0⁰C. 
Water temperature in the sea during the feeding season changes from 21 to 23⁰C in June to 18-21⁰C in September.
Quantitative characteristics of growth. Growth is the most rapid during the first two years of life. Beginning from the third and, specifically in the fourth year, growth rate decelerates noticeably because of mass maturation. Weight gain is most significant in the second and third years. Relation between body weight and length is described by the equation W=0.027*l^2.935

Linear and weight gain of oriental bream (inverse calculations)
(M.A.Sidorova, unpublished data)

Abramis brama orientalis grows rapidly during summer months (June-August) and in September. Growth increment during these months constitutes up to 75-85% of the annual value.

Structural and functional population characteristics

Sex ratio. Males prevail in younger age groups of the spawning population. Males at the age of 3 years old account, on average, for 61.5%, at the age of 4-5 years - 50% of population number. The relative abundance of males further decreases. In general, there is no considerable domination of one sex in the spawning population, i.e., the sex ratio is close to 1:1.
Size- age structure. The Volga bream (spawning population) varies in length from 17 to 49 cm, from 170 to 2,060 g in weight. Individuals over 40 cm TL are rare; most fish are 23-33 cm TL. Bream is a fish of medium-length life cycle. The spawning population consists of 2-12 year-old fish, fish aged 3-6 years prevail. Older fish (9-12 year) are scarce. Mean length, weight and age in the spawning population vary within 28.0-30.0 cm, 470-600 g and 4.5-5.2 years, respectively.

Age composition of the spawning population of oriental bream in the Volga River delta, %
(M.A. Sidorova, unpublished data)

Quantitative characteristics. The Volga River population of Abramis brama orientalis is the most abundant in the Caspian Sea. Its abundance depends on a lot of factors of which the most important are: hydrological conditions in the rivers and seawater level. In mid-1970-s, a decrease of the Volga River discharges and drop in seawater level reached their minimum. During that period, a drastic decline in the stock of oriental bream was recorded. Large volumes of runoff repeated during 1980-s -1990-s, positively affected the spawning success of bream. A rise in seawater level and associated increase in the North Caspian area (including freshened zones) provided favorable conditions for feeding at sea. The catches of bream in 1990-s increased. In 2001, the commercial stock of bream was estimated to be 58,000 tons.

Catches of oriental bream in the North Caspian, thousand tons

Population trends. In 2002-2003, the abundance of Abramis brama orientalis is expected to grow due to its reproductive success in 1997-2000 (large volumes of spring flood and a long flood periods).

Interspecific relations

Bream is a prey fish for some predatory fish (zander, asp, catfish, pike) as well as for birds (cormorant and others). Bream juveniles are consumed by the Caspian seal (0.2%) and beluga (Polyaninova, 1985).
During the summer period, Abramis brama orientalis competes with the other benthivorous fish species (roach, juvenile stellate and Russian sturgeons, gobies) for crustaceans (Cumacea, Corophiidae, Gammaridae), mollusks (H. angusticostata, H. vitrea), worms (Ampharetidae, Oligochaeta) at the North Caspian feeding grounds - food affinity index can reach 50%. Competition is less pronounced in adult breams. Currently, food competition in the North Caspian is not regarded as intensive due to relatively low abundance of sturgeons and other semianadromous fish species.

Food affinity (%) between oriental bream and benthivorous fish of the North Caspian (1974-1979) (Polyaninova et al., 1985)

Importance of subspecies to bioresources production of the Caspian Sea

Economic significance of subspecies. Abramis brama orientalis is a commercially important fish of the Caspian.
It is referred to medium-rich fish; processed as canned product, smoked fish, canned roe.
Commercial characteristics of subspecies, catches. Bream dominates in catches of freshwater species (40% of the total harvest). Over the past decade, catches of bream in the Volga and Ural Rivers varied within 15,200-27,400 tons. The largest yield was recorded between 1994-1997, 23,200 -27,400 tons.
Fishing gears and fishing zones. Bream fishing is conducted in the Volga and Ural Rivers using beach seines in spring (April, May) and autumn (September-October). It is taken from the shallow area of the sea and delta front with fyke nets and fixed nets, from the Kizlyar Bay and at the coast of Kalmykia using fyke nets and drag nets. Catches in these areas are not large (600-700 tons).

Impact of fisheries on the population status

Commercial harvests extract mainly mature individuals of oriental bream. Stable commercial and biological characteristics of the spawning population indicate the sustainable utilization of its commercial stocks. Some 27-30% of the commercial stock is harvested, which does not exceed natural mortality in medium age groups.
Human impact/Threats. Changes in flood conditions due to the Volga River damming adversely impacted spawning grounds and reproduction of bream. Development of agriculture in the delta resulted in the reduction of spawning areas and degradation of reproductive conditions.
Unfavorable toxicological conditions also negatively affect Abramis brama orientalis. Its muscles and liver are revealed to accumulate such contaminants as DDT, organochlorine pesticides, zinc. Xenobiotics retained by fish may disturb its functional state.
Conservation measures:

1. fulfill fisheries requirements to water discharges in the Volga River delta during spring and summer;
2. carry out fine reclamation of spawning sites in the Volga River delta;
3. ban oil and gas field development in the delta;
4. observe fixed quotas on bream catches.

References

Alabaster, D.Sh. and F. Lloyd, 1984. Criteria of water quality for freshwater fish. Food Industry. Moscow. 343 p.(in Russian)
Berg, L.S. 1949. Freshwater fish of the USSR and adjoining states. USSR AS. Part 2. Moscow-Leningrad. P.p. 774-780 (in Russian).
Berg, L.S. 1952. Aral bream (Abramis brama orientalis B.) VNIRO Press. Vol. 30. Pp. 71-73 (in Russian)
Birshtein, Ya. A. Feeding of benthic feeding fish of the Caspian Sea (beside sturgeons) during 1948-1949 and their use of Nereis Sussinea. In: Accklimatization of Nereis in the Caspian Sea. MOIP. Moscow. Pp. 115-144 (in Russian) 
Belova, L.N. and M.K. Popova, 1985. Fish feeding. Roach. Bream. In: Caspian sea. Fauna and biological productivity. Nauka Press. Moscow. Pp. 187-209 (in Russian)
Belova, L.N. and A.A. Polyaninova, 1985. Food relations between benthic feeding fish in the Northern Caspian. In: Caspian Sea. Fauna and biological productivity. Nauka Press. Moscow. Pp. 248-256 (in Russian)
Grib, A.V. and M.F. Vernidub, 1935. On the taxonomy and biology of bream (Abramis brama L.) in the eastern part of the Gulf of Finland. ASU Scientific Notes. Biology, 1: 106-120.
Kessler, K.F., 1872. Abramis brama. News of the Society of Naturalists, X, 1: 68.
Klyashtorin, L.B. 1982. Water respiration and oxygen consumption of fish. Light and Food Industry. Moscow.
Sidorova, M.A. 1980. Distribution of bream Abramis brama orientalis B. in the Northern Caspian. CaspNIRKH Proceedings, Vol. 26: 162-167.
Zhukhinsky, V.N. Impact of abiotic factors on the diversity and viability of fish in early ontogenesis. Agropromizdat. Moscow. 243 p

Compiled by:

M.A. Sidorova (CaspNIRKh, Astrakhan, Russia)

Acknowledgements:

The author is grateful to L.N. Belova, L.V. Malinovskaya and E.V. Kravchenko for providing data on fish food supply and feeding.