A study on the relationships between fish stomach content and stream benthic macroinvertebrate fauna

Stomach content of benthic fish species (Barbus cyclolepis, Heckel 1837 and Gobio bulgaricus Drensky, 1926) and macroinvertebrate species within fauna were investigated in Karasu Creek flow into Büyükçekmece Lake. The benthic organism as stomach content with sedimentary benthic macroinvertebrates were compared each other and possible association between these two content were investigated. Electroshock fishing were performed in designated stations on Karasu Creek in seasonal periods and repeated for 3 days in a row. Moreover, samples were obtained by Surber sampling. Empty stomach (VI) and Index of fulness (FI) and relative importance index (IRI) were used to evaluate fish diet while Schoener İndex were used to evaluate the inter species food competition between species. Electivity Index was used to compare the stomach content of fishes and sedimental macroinvertebrates. 70 Barbus cyclolepis were obtained for the study. Fish ages were distributed between the 0 and III groups. Standard length values were 3.5-13.5 cm and weight values were changed 1.2232-50.8213 g. Female:Male ratio was 1:0.94. Lenght-weight relation for all subjects detected as W=0,0253*SL2,9226. The lowest condition factors were detected in the III age group for females (1,982), highest condition factor values were detected in the I age group for males (2,288). 59 of 70 (84,29 %) Barbus cyclolepis had full digestive tract but 11 of them (15,71 %) had empty tract. In terms of individual ratio the most common invertebrate in the stomach was "Insecta (N % : 97.81)". 90 Gobio bulgaricus were obtained for the study. Fish ages distributed to I-IV groups. Standard length values ranged between 2.5 and 9.6 cm, and weight values ranged from 0.2989 to 18.3014 g. Female:Male ratio were 1:1,56. Lenght-weight relation for all subjects detected as W=0,0209*SL3,0081. The lowest condition factor was detected in the II age group for females (1,950), highest condition factor values were detected in the IV age group formales (2,191). 63 of 90 (70 %) Gobio bulgaricus had full digestive tract but 27 of them (30 %) had empty tract. In terms of individual ratio the most common invertebrate in the stomach was "Insecta (N % : 91,13)". There were significant association of seasonal dietary groups between two species according to Schoener Index comparement. Insecta was dominant group as individual ratio (N) in spring season while "Molusca" was dominant group in summer, autumn and winter seasons according to invertebrate distribution of sediman layer. Again, "Mollusca" was the most dominant group in all seasons but "Entognatha" was the least frequent group. Moreover, dietary groups and sediman species were compared by Electivity Index. According to the findings, Barbus cyclolepis prefers "Digested Insecta fragments" in summer, autumn and spring but "Diptera" in winter whereas Gobio bulgaricus species prefers "Diptera" in summer and winter but "Gastropoda" in autumn and "Digested Insecta fragments" in spring.