Natural feeding habit of the Persian sturgeon (Acipenser persicus) in the southern Caspian Sea in different length classes

Feeding regime of 55 Persian sturgeon caught from southern basins of the Caspian Sea was studied in 3 length classes of <30, 30-60 cm and >60cm. Fish were sampled using bottom trawl at 85 sampling sites at depths varying from 2 to 100m. Food organisms identified in gut contents belonged to families of Gobiidae, Mysidae, Gammaridae, Nereidae, Ampharetidae, Psudocumidae, Clupaidae, Syngnathidae, Scorbicularidae, Cardidae and insects. Our study revealed that feed diversity decreases with increase in length e.g. 8 food items were observed at length class 1 while fish at length group of II and III fed on 5 and 2 items respectively. Mysidae, Gobiidae and Nereidae were the dominant food at length class below 30 cm and for those fish categorized at 30- 60 cm length class the dominant food was Gobiidae and Mysidae. Family Gobiidae was the dominant food for fish in length class over 60 cm. Mean values of gut vacuity index (CV) for length class 1 was 28 which refers to a good feeding condition. This index in length class 2 and 3 were 4.54 and 50 respectively refering to an intermediary feeding condition.