This paper gives the first detailed data on the number and body part related distribution of superficial neuromasts in twelve common European Cypriniform species and examines whether such anatomical variables can be related to rough scale habitat occurrence. The fishes (Barbatula barbatula, Barbus barbus, Chondrostoma nasus, Cobitis taenia, Leuciscus cephalus, Leuciscus leuciscus, Phoxinus phoxinus, Rutilus rutilus, Rhodeus sericeus, Scardinius erythrophthalmus, Tinca tinca, Vimba vimba) were classified in two generalized 'ecological guilds', 1) rheophilic and 2) limnophilic or indifferent, based on literature data. The total number of superficial neuromasts was consistent within each species, but differed considerably between species. Lowest numbers of superficial neuromasts were found in Barbatula barbatula (21 ± 4.9 superficial neuromasts per cm body length) (mean ± SD), highest numbers in Vimba vimba (233 ± 36.1). Both species can be classified as rheophilic. Over all no relationship was found between the total number of superficial neuromasts and large scale habitat occurrence. IntroductionThe lateral line is a hydrodynamic sensory system unique to fishes and aquatic amphibians. Fish use lateral line information for many behaviours, including spatial orientation, rheotaxis, station holding, schooling, prey detection, predator avoidance and intraspecific communication (for review see BLECKMANN, 1994). The smallest sensory receptor of the lateral line is the neuromast, a sensory structure that occurs freestanding on the skin (superficial neuromast or SN) or in sub-epidermal fluid-filled canals (canal neuromast or CN) that open to the environment through a series of pores. SNs usually occur in distinct lines or groups on the head, trunk and tail fin, while lateral line canals often form a network over the head and occur as a single canal on the trunk (reviewed by COOMBS et al., 1988; MONT-GOMERY et al., 1995). Although our knowledge on the anatomy of the SN-system is relatively limited, it is well known that it shows a high diversity. Fish may have only a few or up to several thousand SNs located on the head, trunk and tail fin (for reviews see COOMBS et al., 1988;WEBB, 1989

1. We hypothesised that increased flow in the main stem of the River Rhine would influence the invertebrate communities of its tributaries and therefore investigated the invertebrate fauna of six tributaries over 2 years. 2. We collected quantitative invertebrate samples at three sites in each tributary: in the tributary mouth (influenced by Rhine water whenever flow in the Rhine exceeded mean annual level), in the zone reached by average floods (return period 1.5 years) in the Rhine (average flood level sites), and immediately upstream of the range of extreme Rhine floods (reference sites). Samples were taken in spring, summer and autumn of each year, at different flow levels of the Rhine. We also compared substratum composition at the three sites. 3. Tributary mouth sites had the finest substratum, the lowest total invertebrate density and the lowest taxon richness. At average flood level and reference sites, these three parameters were similar. 4. Taxa known to prefer larger rivers were mostly confined to the tributary mouth sites, and species preferring upland streams dominated at the average flood level and reference sites. 5. Multivariate analyses confirmed the influence of the Rhine on the tributary mouth sites. Invasive invertebrate species, which usually appear only in the Rhine itself, were found at the tributary mouth sites but not further up in the tributaries. 6. Our study shows that increased flow in the main stem of the Rhine influenced substratum composition and invertebrate communities at the tributary mouth sites. These results imply that the relationship between the main stem of a river and its tributaries is not one-way (from tributary to main stem), but rather a two-way interaction.

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