The Diel Changes in Feeding Activity, Microhabitat Preferences and Abundance of Two Freshwater Fish Species in Small Temperate Streams (Omerli, Istanbul)

Abstract

We examined the abundance, food and microhabitat use of Proterorhinus marmoratus (Gobiidae) and Cobitis vardarensis (Cobitidae) during both day and night in two small temperate streams of the Black Sea region (North-West Turkey) between May and June 2005. Drift sampling catch per unit effort revealed significantly higher relative densities at night than during the day. Of the 110 fish captured during the seven sampling periods, 77 (88%) were C. vardarensis with the Býcký Stream having the most fish specimens both in frequency of occurrence and relative density. The main environmental variables that characterized the overall microhabitat use were velocity, light, depth, and proportions of cobbles. The fullness frequency of the gut contents was at their peak between 22:00 and 04:00 a.m and the most active feeding time was usually after midnight. Surface insects composed mainly of chirinomid larvae were the dominant food item for both species in the streams during the sampling period. Further studies are needed at multiple spatial scales to assess how habitat use and feeding habits varies with fluctuating population densities.