| Summary: | The effect of diel period (i.e. day vs. night) and its dependence on the spatial position of the sampling site were evaluated on the assessment of fish assemblage attributes in a wadeable lowland stream (Hajagos stream, Hungary). Species richness, composition and abundance data of two 150 m long reaches, of which one situated directly at the tributary mouth and one 6 km upstream were compared using three pass removal by electrofishing in three seasons (summer, autumn, spring) to test the effect of spatial position on day and night patterns. No differences in any assemblage level variables were found between day and night. Although fish assemblages showed large temporal variations, spatial position of the sampling site had the most influential effect on fish assemblage attributes compared with seasonal and/or day night patterns. Consequently, the diel period had rather negligible effect in the studied stream. Daytime electrofishing data seems to be highly representative for the accurate assessment of fish assemblages in relatively small (less than 5 m wide) wadeable streams and maybe used reliably for any model of community organization (e.g. food web studies).
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