On the occurrence, diet and reproduction of Neogobius fluviatilis in Madarsoo stream, Golestan National Park (north eastern Iran)

Abstract

The abundance of Neogobius fluviatilis in the Madarsoo stream ranged from 0.1 to 0.75 specimens per m² and fish biomass from 0.21 to 4.88 g per m². The rate of growth displayed sexrelated differences. Chironomidae, Ephemeroptera and Trichoptera were the most abundant benthic invertebrates among 10 categories of collected organisms. The Ivelev Index showed that Ephemeroptera with 0.2–0.8 and Chironomidae with 0.2 were the most important food items for N. fluviatilis. The Shannon Diversity Index for food items ranged from 0.04 in June to 0.56 in May. It was shown that as diversity of potential food organisms in the stream bed increases, so diversity in gut increases too. Based on the Gonado Somatic Index, the spawning peak was found to be in March, which is earlier than in other areas in the Caspian basin. The sex ratio was 1 male to 3 females, which is different from other areas in the Caspian basin.