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About 30 species of economic fishes have been caught in the sea waters of Guilan province annually; the most important of them included kutum fish (Rutilus kutum), golden grey mullet (Chelon auratus) and sharp-nosed grey mullet (C. saliens). The aim of this study was to determine the food spectrum and dominant food items of these fishes on the shores of Guilan province. The fish were captured with seine net with mesh sizes 6, 20 and 33 mm in the shores of Talesh, Anzali, Kiashahr and Chabaksar from winter 2020 to autumn 2021. The results showed that in R. kutum coefficient of vacuity index (CV) was calculated 1, 9 and 28%, the mean the Relative Length of Gut (RLG), was 0.78, 0.86 and 0.87 and the mean intensity of fullness (IF) 392, 226, and 73 in the age group of 0+-1, 2-3 and 4-6 years old, respectively. Filamentous algae, 13 types of benthic, 26 genera of phytoplankton, 2 types of zooplankton as well as fish (eggs and larvae) were identified in the percentage of 73, 86, 62, 5, and 2% respectively were observed in the gastrointestinal tract of R. kutum in size group of 3-12 cm (261 specimens). The family Cardiidae from benthos, the genera of Navicula, Nitzschia and Rhoicosphenia from phytoplankton included the dominance of 34.1, 25.5 and 11.9% and bivalve larvae included 99.3% of zooplankton number. In the gastrointestinal tract of R. kutum, in size group of 22 -48 cm (101 specimens), only 4 types of preys have been found and all of them were benthos including bivalve, Cerastoderma glaucum and 3 types of crustacean, Balanus improvensis (Balanidae), Gammaridae and crab, Rhithropanopeus harrisii, that C. glaucum and B. improvensis constituted about 89.7% and 9.9% of total benthos, respectively. In Chelon auratus, was calculated the vacuity index was 4, 0 and 0%, respectively, the mean relative length of gut, 1.23, 2.39 and 2.82 and the mean intensity of fullness 522, 472 and 186 in group ages of + 0, 1-2 and 3-6 years old, respectively. In the digestive tract of C. auratus in group age of lower than 7 cm total length (n=118), detritus, 5 types of benthic, 27 genera of phytoplankton and 7 types of zooplankton were identified, which were observed in 54, 34, 100 and 71% of the studied fish, respectively. Gammaridae and Chironomidae with 48% and 34% of benthic numbers; Nitzschia and Navicula included 32.6% and 32.3% of phytoplankton cells and naupli of Acartia included with 79.8% of zooplankton numbers were dominant. In the gastrointestinal tract of 7-15 cm total length (n=43), detritus, 2 types of benthic, 22 genera of phytoplankton and 3 types of zooplankton were identified, which were observed in 62, 4, 100 and 20% of the studied C. auratus, respectively. It was abundant Foraminifera with 67% of benthic numbers, Nitzschia and Navicula included 35.6% and 34.2% of phytoplankton cells and naupli of Copepods included 79.8% of zooplanktons, respectively. In the gastrointestinal tract of bigger than 15 cm specimens of C. auratus (50 specimens), detritus, 4 types of benthic, 33 genera of phytoplankton and 6 types of zooplanktons were identified which were observed in 98, 4, 100 and 54% of the fish numbers, respectively. Foraminifera, Cerastoderma and unidentified bivalves comprised 36.7%, 20.4% and 30.6% of benthic numbers, respectively, the genera Binuclearia, Exuviaella and Synedra were dominant with 44.6%, 8.1% and 8% of phytoplankton cells and nauplius of Copepod was abundant with 83.9% of zooplankton numbers. In Chelon saliens, was calculated vacuity index 14, 10 and 13%, mean relative length of gut, 1.11, 1.37 and 1.47 and the mean intensity of fullness was 400, 348 and 487, in group ages of 0+, 1-2 and 3-6 years old, respectively, and there was significant differences among age groups, among seasons and among stations. There was detritus, 5 types of benthic, 23 genera of phytoplankton and 9 types of zooplankton in the gastrointestinal tract of C. saliens in lower 7 cm length group (n=318), which were observed in 22, 47, 100 and 69% of the fish specimens, respectively. Cardiidae and Gammaridae were dominant with 55.7% and 26.1% of benthic numbers, Oscillatoria, Navicula and Cyclotella were dominant with the percentage of 37.9%, 14.2% and 12.5% of phytoplankton cells, and nauplius of Copepods was abundant with 95% of zooplankton numbers. In the gastrointestinal tract of 7-14 cm length group of C. saliens (n=162 specimens), detritus, 8 types of benthic, 24 genera of phytoplankton and 7 types of zooplankton were identified, which were observed in 20, 57, 100 and 30% of the studied fish, respectively. Cardiidae and Tubifex worm established 41.6% and 28.7% of benthic numbers, the genera of Navicula and Nitzschia with 29.8% and 20.3% of phytoplankton cells were dominated among phytoplankton and nauplius of Copepods and bivalve larvae made 57.5% and 25.1% of zooplankton numbers, respectively as dominant groups. In the gastrointestinal tract of bigger than 14 cm length group of C. saliens (165 specimens), detritus, 9 benthic species, 32 genera of phytoplankton and 10 types of zooplankton were identified, which were observed in 24, 73, 100 and 37% of this fish species, respectively. Foraminifera and Cardiidae with 58.1 and 31.5% of benthic numbers, involved as dominant groups. The genera of Navicula and Nitzschia with 23.8% and 19.3% of cell numbers were dominated among phytoplankton and bivalve larvae and Foraminifera with 37.7% and 33.5% included among the dominant group of zooplankton numbers. In general, it can be said that the intensity of fullness and also the dietary diversity of small to large specimens of all studied species (except R. kutum adults), was appropriate in the coasts of Guilan province. Vacuity index, relative length of gut and intensity of fullness usually variation among age groups, seasons and stations were observed, but station variations were relatively insignificant in all three species. Phytoplankton diversity was also similar in all specimens (between 22 and 33 genera) but the diversity of benthic and zooplankton, both it was often different among species and among longitudinal or age groups in any species, too. The study found that juvenile R. kutum is a benthivore and algae-feeder but adults are benthivore. Chelon auratus is omnivorous mostly detritvore, an C. saliens were omnivorous mostly carnivorous and benthivore.
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