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Chitgar lake is the biggest urban lake in Iran with a surface 130 hectare and located in Tehran City. This study has been done inside the lake and its tributary river (Kan), in September 2017, and May and November 2018 and March 2019, and the main porposes were identification, dispersion, abundance, length, weight and age composition, sex ratio, reproduction and diet of fish species. Gill-nets, beach seine and cast-net inside the lake and electroshocker inside the river used for sampling in 3, 10, 10 and 3 stations, too. Results showed 17 species belong to 7 fish families (Cyprinidae, Pangasiidae, Bagridae, Clariidae, Loricariidae, Esocidae and Characidae) which of them, Cyprinidae has the most diversity with 11 species. One, 3 and 13 speceis were endemic, native and exotic respectively and among exotic fishes, 4, 3 and 6 were accidental , ornamental ones and introduced for aquaculture propose. Fish species were nearly distributed in all stations. Hemiculter leucisculus and Cyprinus carpio were abundant with gill-nets with 72.5% and 13.8%, H. leucisculus and Alburnus hohenackeri were abundant with beach seine with 70.6% and 15.3% and H. leucisculus, Pseudorasbora parva and Carassius gibelio were abundant with cast net with 47.0%, 21.0% and 20.0% of caught fish specimens, too. The averages of total length was determinated 8.3±1.9, 10.8±3.9, 20.5±2.6, 34.1±11.8, 13.4±5.4, 4.3±1.8 and 51.9±10.9 cm, body weight 5.9±3.2, 23.3±23.1, 138.4±50.5, 944.6±1372, 26.1±26.5, 1.1±1.5 and 1138.1±838 g and condition factor 0.91±0.1, 1.32±0.1, 1.55±0.2, 1.64±0.2, 0.72±0.1, 0.88±0.1 and 0.77±0.1 in A. hohenackeri, Capoeta buhsei, C. gibelio, C. carpio, H. leucisculus, P.parva and Esox lucius respectively, too. Total length, body weight and condition factor have had significant differences among seasons and between males and females of 5 species (A. hohenackeri, C. carpio, H. leucisculus, P. parva and E. lucius). A. hohenackeri and P. parva age range were 0+ to 4+, C. buhsei and E. lucius 0+ to 5+, C. gibelio 2+ to 5+, C. carpio 0+ to 9+ and H. leucisculus 0+ to 9+ years old. Growth was assessed isometric in C. buhsei, C. gibelio, C. carpio, Hypophthalmichthys molitrix and P. parva, negative allometric in A. hohenackeri and positive allometric in H. leucisculus and E. lucius. Female ratio was more than males in C. gibelio and H. leucisculus, males were dominant in C. buhsei, C. carpio and P. parva but the others had not difference with standard amount (1female:1male), too. Spawning season was determinated in spring for A. hohenackeri, C. buhsei, C. gibelio and P. parva, in spring and summer for C. carpio and H. leucisculus and last autumn and winter for E. lucius, though it seemed reproductive activities were incomplete in C. gibelio, C. carpio and E. lucius according low abundance of small-sized specimens (0+). Maturity took place in 1, 2, 2, 3, 2, 1 and 2 years old of life in females of A. hohenackeri, C. buhsei, C. gibelio, C. carpio, H. leucisculus, P. parva and E. luciusrespectively. Annual fecundity was estimated 1133-2909 (2151.7±589.3) eggs in A. hohenackeri, 8822-12587 (9853.4±1606) eggs in C. buhsei, 64964-2111152 (382666±450565) eggs in C. carpio and 20820-51753 (36619.6±10297) eggs in H. leucisculus and absolute fecundity was 29727-136170 (65689±31743) eggs in E. Lucius. The intensinity of fullness was determinated 211, 208, 216, 109, 279, 628, 278 and 170 for A. hohenackeri, C. buhsei, C. gibelio, C. carpio, H. leucisculus, H. molitrix, P. parva and E. Lucius, respectively that showed high , medium, medium and relatively weak feeding in H. molitrix, H. leucisculus, P. parva and the other species. The study of food composition in gut of dominant fish species in Chitgar lake showed 5, 30 and 5 benthos, algae and zooplankton genera in the gut of A. hohenackeri, 7, 17 and 4 benthos, algae and zooplankton genera in the gut of C. buhsei, 2, 32 and 11 benthos, algae and zooplankton genera in the gut of C. gibelio, 10, 26, 10 and 3 benthos, algae, zooplankton and fish genera in the gut of C. carpio, 9, 30, 11 and 1 benthos, algae, zooplankton and fish genera in the gut of H. leucisculus, 32 and 11 algae and zooplankton genera in the gut of H. molitrix, 2, 26 and 11 benthos, algae and zooplankton genera in the gut of P. parva and 1 and 5 benthos and fish genera in the gut of E. lucius, respectively. Thus in Chitgar lake were A. hohenackeri, C. buhsei, C. carpio and H. leucisculus as omnivorous, C. gibelio, H. molitrix and P. parva as planktivorous and E. lucius as carnivorous fishes, too. It is suggested annual releasing of necessary immature individuals of silver carp (for control of phytoplankton) and pike (for control of small-sized unwanted fish populatins such as H. leucisculus and P. parva) in order to improve of water quality of Chitgar lake.Keywords: Chitgar Lake, Fish, Abundance, Diet, Reproduction.
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