Liza aurata, (Risso, 1810)

Taxonomic description of species

Head rounded in section. Head scales large, reach posterior nostril, scale on back and head has one canal in the middle. DI VI, II 6-7, A III (7) 8-9. Color: several golden longitudinal stripes on sides, big golden spot at upper edge of operculum.
Intraspecific forms. None
Related forms. Liza saliens (Risso, 1810)- leaping grey mullet.

Distribution of species within the Caspian Sea

Distributed in the Middle and South Caspian Sea. Single specimens occur in the North Caspian.
Status as per International Red Data Book. N/A
Status as per National Red Data Books. N/A
First record for the Caspian Sea. 1933, eastern coast of the Caspian, Krasnovodsk region (cited: Karpevich, 1975)
Redescription of species. Berg, 1949:998

General characteristics of species

Ecologo-taxonomic group. Nekton. 
Origin. In 1931-1934, juveniles of golden grey mullet were introduced into the Caspian from the Black Sea (targeted introduction).
World distribution. The Atlantic Ocean, from England up to the South Africa, Mediterranean, Black and Azov Seas.
Habitat. Pelagic zone.
During migration and spawning, adult fish inhabit pelagic zone of the sea at the depth of 5-700m. During the feeding/ fattening period the older juveniles and adult fish dwell at the bottom of coastal waters, depths - 0.5-30m.
Migrations. Winters in the southern part of the South Caspian, mostly at the Iranian coastal waters. In March, as soon as the water gets warmer, feeding migration starts along the shallow areas of the eastern and western coasts to the Middle Caspian (appears there in April). Then it migrates to the North up to the Mangyshlak Peninsular and islands Chechen and Tyuleniy (in the end of May). In June-July, it is found in the vicinity of Maly Zhemchuzhny island. During migration keeps in small shoals at the surface water layers and feeds actively. In September-October the mature fish migrate to the deepwater part of the Middle and South Caspian (300-700 m deep), where spawning occurs. The young fish do not undertake considerable migrations.

Relation to abiotic environmental factors

Relation to salinity. Euryhaline fish species, occurs both in fresh water (0.05⁰/₀₀, the Dnieper river near Kherson ) and in highly salinated water bodies (57⁰/₀₀, Lake Sivash). Mass mortality is recorded at salinity rate 65⁰/₀₀. In the Caspian Sea resides at salinities ranging from 3 -5⁰/₀₀ to 13-14⁰/₀₀.
Relation to temperature. Thermophilic warm-water species.
The optimum temperature is 23-25^oC. The fish cease feeding at 6-8^oC, lose mobility at water temperatures 2-3^oC and dies at 1-1.5^oC.
Juveniles are found in shallow water at water temperature 37.5^oC (Probatova, Tereschenko, 1951)
Vertical distribution. Adult fish and older juveniles keep mostly in shallow coastal areas at depths 0.5-30 m, in winter move to the depths 50-100 m. Spawning and development occur above the depths 300-700 m.
Relation to oxygen conditions. Less sensitive to concentration of dissolved oxygen than some other fish species. Occurs in lagoons, where oxygen concentration does not exceed 2.3 cm3*l^-1. Survived under experimental conditions at oxygen concentration 0.35 cm3*l^-1 (Tomozo, 1940).
Relation to fluctuations of the sea level. Sea level rise results in the increase of coastal shallow areas and the expansion of the feeding grounds.

Feeding

Feeding type. Detritophagous
Feeding behavior. Pasturing 
Food spectrum. Larvae and fry (0.5-2,0 cm TL) feed on plankton and detritus at the water surface. Diatoms, larvae of mollusks, plankton crustaceans prevail in the diet. When larvae attain 2.0-6.0 cm TL, they move to the coastal area, where they feed both on plankton and benthic organisms (Gammaridae, larvae of Chironomidae, worms). Further, detritus becomes the major food item. Adult fish scrape off the fouling organisms (periphyton) from rocks and silt. Mollusks (Hydrobia and others) and worms (Nereis) are included in the food spectrum as well. 
Food supply. Unlimited 
Quantitative characteristics of feeding. N/A

Reproduction

Reproduction type. Sexual 
Reproduction areas. The central area of the South and Middle Caspian
Terms of reproduction. Spawning takes place from July till October in the upper surface (up to 0.5 m) layer above the depths 300-700 m at water temperature 25.6-29.4⁰C, salinity value - 13⁰/₀₀. Reproduction process peaks in the second half of September.
Fecundity. Fecundity ranges from 158*10³ to 4440*10³ eggs. Pelagic eggs are small (diameter 0.6-0.9 mm), keep in the upper 0.5 m layer. Single eggs are found in 1.6-m layer.
Limiting factors. Wind-induced waves, abrupt change of the temperature, consuming eggs by different plankton organisms.

Life history and development

Life history stages. The species is characterized with the short embryonic period. In twenty-four hours after fertilization (at water temperature 21⁰C), the body of the embryo is segmented, eyes present. By the next twenty-four hours, hatching occurs. The length of the larva is 2.4 mm. Fingerlings reach the length 2-3 cm by the end of October, yearlings attain 4.4 cm TL by May.
Relation to environmental factors. In fresh water the eggs of golden grey mullet are not capable to be fertilized, and die. The roe loses its floating capability and drowns at salinity less 8.82 ⁰/₀₀. Mortality of embryos and larvae increases drastically when the water temperature drops abruptly.
Age of maturity. Maturation occurs at the minimum age of three years, generally at the age of 4-6 years.
Thermal conditions of development. N/A
Quantitative characteristics of growth. As the golden grey mullet reproduces in autumn, the growth of fry during the first months (winter) is very low. Growth rate increases in the forthcoming spring and peaks in July-August. The rapid growth continues until the fish are 3-4 years old. Growth rate slows down considerably after the first spawning occurs.

Linear growth of golden grey mullet
(Cited: Dubrovina, 1951)

Structural and functional population characteristics

Sex ratio. At the age of 3-4 years, sex ratio is equal to 1:1 (data for the North Caspian), the number of females in senior age groups (5-8 years) exceed that of the males 3-7-fold. In average, for all age groups the sex ratio was estimated as 1:2.
Age-size structure. In the Caspian Sea golden grey mullet reaches the age of 11-12 years old, usually 9-10 years. TL of females amounts to 55 cm, weight - 2.5 kg, that of the males - 43 cm and 1.26 kg, respectively. (Tereschenko, 1950; Dubrovina, 1951). In 1999, the average TL of fish in the North Caspian corresponded to 38.7 cm, weight - 924.4 g. The majority was represented by fish 3 - 8 years old. 
Quantitative characteristics. An abundant, widespread fish species in the Middle and South Caspian
Population trends. No decline in abundance was observed.

Interspecific relations

Young fish represent a food item of zander and catfish; adult fish is recorded in the diet of beluga.

Importance of species to bioresources production of the Caspian Sea

Economic significance of species. A valuable commercial fish species
Commercial characteristics of species , catches. The stocks are underused, particularly over the recent years. The maximum number is harvested during winter at the Iranian coast. In 1965-1970, its harvest amounted to 0.72 thousand tons in average, in cold winters increased up to 1.4-1.9 thousand tons. At the Azerbaijani coast grey mullet comes as a by-catch to other commercial fish species, in fixed nets and beach seines. The maximum harvest was recorded in 1957- 1961, 0.25 thousand tons in average, further it showed steady reduction - to 6 tons in 1996-2000. No fishing is executed at present at the Turkmenian coast, where the catches of golden grey mullet accounted to 488 tons in 1950-1954, 303 tons - in 1960-1964. Small numbers are caught sporadically at Mangyshlak peninsula and near the Dagestan coast.
Fishing gears and fishing zones. Harvested with fixed nets and beach seines, haul and circular seines with a pocket, and different traps.

Impact of fisheries on the population status

None.
Human impact/ Threats. The status of population will be substantially disrupted due to considerable pollution of the sea and, specifically, shallow coastal areas. 
Conservation Measures. Reduce level of pollution in the coastal zones of the Caspian sea.

References

Abdurakhmanov, Yu. A. 1962. Fish of freshwater bodies of Azerbaijan Azerbaijan SSR AS Press. Baku. 407 p. 
Adburakhmanov, Yu. A. 1966. Fish of Azerbaijan Baku. Azerbaijan SSR AS Press. Baku. 224 p. ( in Azerbaijani).
Avanesov, E.M. 1972. The present conditions grey mullet reproduction (the genus Mugil ) in the Caspian Sea. Voprosy Ikhtiologii (Problems of Ichthyology). Vol.12, 3: 464-470
Badamshin, B.I. 1938. Mullet and its fry in the waters of Mangyshlak area. Rybnoye Khozyaistvo (Fisheries), 2: 37-38 
Berg L.S. 1949 Fish of freshwater bodies of the USSR and adjacent states. Part 3 . USSR AS. Noscow-Leningrad. P.p. 930-1382
Dubrovina, I.A. 1951. Mullet in the Northern Caspian and at the Kazakhstan coast of the Caspian Sea. VNIRO Proceedings. Vol. 18: 135-146
Khoroshko, A.I. 1989. Mullet. In: Caspian Sea. Ichthyofauna and commercial stocks. Nauka Press. Moscow. P.p. 178-184
Kudelina, E.N. 1950. Mullet feeding in the Southern Caspian. Proceedings of the Caspian Basin Branch of VNIRO. Vol. 11: 87-108
Kuliev, Z.M. 1989. Fish of the Kirov Bay of the Caspian Sea. ELM Press. Baku. 184 p.
Pertseva-Ostroumova, T.A. 1951. On the reproduction and development of mullet introduced in the Caspian Sea . VNIRO Proceedings. Vol. 18.
Probatov, S.N. 1953. The results of the air exploring of Caspian mullet and possibilities of its fishing on the routes of migration. Rybnoye Khozyaistvo (Fisheries), 8:18-22
Probatov, S.N. and Z.P. Tereshchenko, 1951. Mullet in the Caspian Sea and its fishing. Pishchepromizdat. Moscow. 36 p.
Tereshchenko, Z.P. 1950. The materials on biology and fishing of the Caspian mullet. Proceedings of the VNIRO Caspian Basin Branch. Vol. 11, p.p. 49-86
Tomozo, G.I. 1940. Mullets (Mugilidae) in the north-eastern part of the Black Sea. Proceedings of theNovor.Biol .St. Vol. 2, p.p. 81-122

Compiled by:

Z.M. Kuliev (AzerNIRKh, Baku, Azerbaijan)
D.B. Ragimov (Azerbaijan AS, Baku, Azerbaijan)