New approaches for assessing the impacts of non-native freshwater fishes in the Mediterranean region, Muğla, Türkiye, 26 - 29 Ekim 2010, cilt.1, no.1, ss.17
Non-native freshwater fish species may easily be introduced and become one of the important
components of the ichthyofauna of newly created small reservoirs through stocking common
carp, Cyprinus carpio. Although detrimental effects of non-native freshwater fish on native
fish species is very well known world-wide, it is little studied in small artificial water bodies
established for irrigation and drinking water purposes, and there are no known such studies in
Turkey. The present study is the first such attempt, and compares life history traits (condition,
reproduction) and food in six small reservoirs, two containing native fish species only
(allopatry), two containing non-natives only (allopatry), and two with both natives and nonnatives
(sympatry). Body condition (LK) and relative fecundity (per unit of body weight) of
native fish species was greater in allopatry living lonely while they were higher for non-native
species in sympatry living together with natives. Plant and insects were the most common
prey items for native, Squalius cephalus whereas detritus, Gammarus sp., zooplankton eggs
and insects were preferred prey for non-native Carassius gibelio gibel carp, Lepomis gibbosus
pumpkinseed and Pseudorasbora parva. Diet overlap with gibel carp was greatest for chub.
Diet similarity based on taxonomy correlated strongly with diet similarity based on size.
Differences in condition and fecundity between the native and non-native species does not
appear to be due to differences in available food or ecological conditions, so elevated
condition and reproductive output in non-native species in sympatry may be due to nondietary
competitive interactions. The present preliminary study highlights the needs for
further study of effects of non native fishes on native species in small artificial lakes mostly
established on natural stream ecosystems and the potential for negative consequences of nonnative
species should not be underestimated.