Population structure and feeding ecology of endemic gudgeon Gobio insuyanus ladiges, 1960

This study focuses on Gobio insuyanus, a local endemic and endangered fish species native to Turkish freshwaters. Of the 12 Gobio species found in Turkey, 11 are considered endemic to the country. Gobio insuyanus occurs in a few small springs in the Insuyu stream. Individuals collected from the Stream and Spring habitats varied between 16.6 mm and 145.4 mm. The maximum age of the species was determined to be VII, and it was found that I+ age individuals were dominant in the population. In terms of sex ratios, females were found to be dominant in the population (D:E; 1.64:1.00), while the sex of 47 individuals (15.6%) could not be determined. According to the data obtained from 198 fishes whose stomach was analysed, it was found that G. insuyanus is a omnivore that feeds mainly on the adult and larval stages of insects, amphipods and on zooplankton. Seasonal, ontogenetic and habitat (Spring and Stream) differences in the diet composition of the species were observed. While Diptera larvae were the dominant food category in the Stream habitat, Gammaridae individuals were more common in the Spring habitat. Gammarid larvae were dominant in autumn, whereas odonate larvae became dominant in spring. The relative importance of dipteran larvae in the diet was highest in summer. Taking into account the ontogenetic differences in feeding, it was found that adults showed a slightly higher specialisation and therefore a lower diet diversity. The adults fed mainly on gammarids, whereas the juveniles, which had a higher diet diversity, fed mainly on dipteran larvae. There was no significant difference in diet between the sexes. It was found that the trophic level of the species varied between 3.25 and 3.35 when unidentified detritus was excluded from the diet. Keywords: Gobio insuyanus, Population Structure, Feeding Ecology, Endemic Gudgeon