The importance of substrate size and interstitial space in the microhabitat selection by the stream-dwelling catfish Hatcheria macraei (Actinopterygii, Trichomycteridae).

The study tests whether diurnal microhabitat use by Hatcheria macraei depends upon specific environmental parameters and/or the abundance of other fish. We carried out a 1-year field study in a low-order river of northern Patagonia, Pichileufu River, and used experimental trials to determine substrate preferences. Fishes were captured during daylight and physicochemical environmental variables were recorded. Headwater zones were dominated by rainbow trout ( Oncorhynchus mykiss) and brown trout ( Salmo trutta), while native fishes, H. macraei and the creole perch ( Percichthys trucha) were more abundant downstream. H. macraei inhabited mostly shallow microhabitats with fast water velocity and substrates having significant interstitial spaces, independently of the abundance of other fishes. Experimental trials pointed out that H. macraei preferred mostly coarser substrates (>6 cm), avoiding fine ones. This study highlights the importance of erosional zones with high water velocity, large substrates, and suitable interstitial space in the microhabitat selection of H. macraei. The knowledge of microhabitat use by native fish populations is critical for management and conservation strategies and should be taken into account before any river modification. [ABSTRACT FROM AUTHOR]