Rheophilic Fish Research Articles

Groyne-heads as potential summer habitats for juvenile rheophilic fishes in the Lower Oder, Germany

The present study aims to test the hypothesis that artificial structures, the riverward ends of groynes or groyne-heads, function as potential habitats for young rheophilic fish. The investigation was undertaken in summer 1998 on the River Oder, in the Polish-German National Park ‘Lower Oder Valley’, eastern Germany. Fish were caught on groyne-heads using point abundance sampling by electrofishing and compared with specimens collected by the same method in seven additional mesohabitats (navigable side-canal, sandy river bank, riprap, deep groyne, sandy groyne, connected backwater, polder waterbody). Groyne-heads were inhabited by bottom-oriented 0+ rheophilic stone loach Barbatula barbatula (L.) and burbot Lota lota (L.), whereas 0+ rheophilic cyprinid fish were more abundant in shallow-sloped, sandy shoreline mesohabitats. Of all sites investigated, 1+ juveniles were most abundant on groyne-heads, in which the rheophilic group formed a large proportion of the total catch. From our results we conclude that groyne-heads constitute an important habitat for both 0+ and 1+ juvenile rheophilic fish during summer-time, but that its use is limited by the stochastic availability due to varying discharges.

ENVIRONMENTAL AUDITING: The Fish Fauna of the Doubs River Prior to Completion of the Rhine-Rhone Connection

/ The part of the Doubs River between Montbeliard and Dole (France), i.e., downstream from the confluence with the Allan River, will be affected by the Rhine- Rhone connection project. In order to improve the understanding of the Doubs ichthyofauna, aquatic environments of the Doubs were sampled by electrofishing. Fish diversity and the presence of some rheophilic species demonstrated the good ecological quality of some stretches of the Doubs. This quality was due to alternating areas with very diversified aquatic environments (riffles, islands and side-arms, backwaters) and a considerable range of flow velocities. The differences in the structure of the fish communities of the different types of aquatic environments were more qualitative (fish species) than quantitative (number of species and number of fish). However, the mean number of fish was statistically lower in the canals (Freycinet canal and channelized part of the Allan River) than in the main course and in the backwaters. The natural parts of the Doubs (unnavigable reaches) showed the most diversified environmental structure and had the most rheophilic fish communities. Thus, the rheophilic species were well represented, but they proved also the most vulnerable to river regulation. However, the most abundant fishes throughout the Doubs River were generalists with no special requirements for food sources or spawning substrate.KEY WORDS: Fish communities; Regulation; Restoration; Floodplain; Large ship canal; Doubs River

Functional morphology of gills and respiratory area of two active rheophilic fish species, Plagioscion squamosissimus and Prochilodus scrofa

Measurements of gill dimensions were carried out on two ecologically distinct active rheophilic teleost species, the curvina Plagioscion squamosissimus and the curimbatáProchilodus scrofa, and were analysed in relation to body mass according to the equation Y=aWb. The gill respiratory areas of P. squamosissimus and P. scrofa were large as expected for active fish and increased with increasing body mass (b=0.70 and 0.72, respectively) showing no significant difference between them. However, the large respiratory area of both species was realized in a different way revealing an adaptation to the plasticity of head components related to feeding habits. Consequently, significant differences were found between the number and average length of gill filaments and the bilateral area of secondary lamellae. The respiratory area of P. scrofa was due mainly to larger bilateral surface area of the secondary lamellae and its growth coefficient (b=0.51) that was significantly higher (P<0.05) than that found for P. squamosissimus (b= 0.36). The frequency of secondary lamellae mm−1 of filament was similar in both species (22 ± 2 on one side of gill filament). The dimensions of gill components and the respiratory area of these species suggest a complex interaction between head form, and feeding habits related to the functional morphology of the gills to meet the oxygen requirements of each species.

Winter distribution and habitat use by fish in a regulated lowland river system of south‐east England

The macrohabitat preferences of 1+ fish (10 cm FL) and the microhabitat use of 0+ juvenile fishes in the River Lee catchment (UK) were examined from data collected over a 3‐year period between late autumn and early spring using depletion sampling and point abundance sampling, respectively. Canonical correspondence analysis and habitat profiles revealed preferences in the more rheophilous fish species (e.g. brown trout, Salmo trutta L., barbel, Barbus barbus (L.)) for features characteristic of upstream natural channels and meander sections of the by‐passed old river, with the more ubiquitous (e.g. perch, Perca fluviatilis L.) and limnophilous fishes [e.g. pike, Esox lucius L., tench, Tinca tinca (L.)] preferring habitats mainly in downstream channelised stretches. The microhabitat of 0+ juvenile fishes in the River Lee was similar to that reported elsewhere for the same species, influenced mainly by channel width, depth, and distance from the bank, though microhabitat overlap in 0+ roach, Rutilus rutilus (L.), and gudgeon, Gobio gobio (L.), was greater in the Lee than observed in larger, more open river systems.

Effects of reduced oxygen level on the mortality and hatching rate of Chondrostoma nasus embryos

Exposure of embryos of Chondrostoma nasus to a strongly reduced oxygen content (about 10% of air saturation) enhanced mortality and depressed hatching success. Viable larvae hatched only from the controls and from the group exposed to reduced oxygen during the earliest embryogenesis (from fertilization to gastrula). In the groups exposed from gastrula to eyed stage and from eyed stage to hatching, a high percentage of fish hatched, but all were deformed and almost all died during the following 1–5 days. Hatching period was prolonged in the groups exposed to reduced oxygen content. At a spawning area C. nasus had deposited a large portion of eggs in areas of reduced oxygen content. On the other hand, eggs placed at the substratum surface were exposed to high predation pressure from Barbus barbus, Lota lota and ducks (Anas platyrhynchos). The trade‐off between predation pressure at the substratum surface and reduced oxygen conditions in the interstices resulted in a narrow space for successful development of embryos of this endangered rheophilic fish species under natural conditions.

Reactions of dace to linear accelerations

It is demonstrated that the rheophilic fish dace (Leuciscus leuciscus) is able to detect the direction of its movements in a water flow by perceiving and analysing positive and negative accelerations from 15 up to 50 cm s−2, by the use of labyrinth organs. Tests were conducted on fish with ‘switched off’ mechanoreceptors and labyrinth organs, under conditions which eliminated the use of visual orientation. It was also demonstrated that the values of linear accelerations which stimulated dace compensatory movements against water currents were comparable with the values of accelerations which could arise in river flows as a result of pulsation in current velocity. The results support the hypothesis that rheophilic fish are able to use inertial stimuli for their spatial orientation.

Some practical methods for harvesting fish ponds and handling live fish

Methods to simplify the cropping and handling of rheophilic fish and nocturnal prawns, utilizing their behavior are described.