The diet and growth of roach (Rutilus rutilus (L.)) in Lake Vesij�rvi and possible changes in the course of biomanipulation

Abstract

Previous studies have suggested that the roach Rutilus rutilus (L .) stock of Lake Vesijarvi is one of the main factors delaying the recovery of the lake after sewage diversion . This study is concerned with the documentation of the diet of roach in the lake . In total, 531 roach were examined . Both in the pelagial and in the littoral the roach had mixed diets in May and in September-October . The importance of zooplankton decreased and the importance of benthos and plants increased with increasing size of roach . In July, in the pelagic zone all sizes of roach fed exclusively on zooplankton (Bosmina spp .), while in the littoral zooplankton had the highest volume proportions only in the smallest (< 130 mm) roach . The frequent use of plant food and slow growth rate of large roach indicate a low availability of animal prey . As the fish densities decrease due to the mass removal taking place in the lake, the percentage of plant food in the diets of roach will probably decrease and the growth of roach will increase . Additionally, the tendency of the roach to migrate into the pelagic zone in early summer may be reduced, which would decrease their predation on the zooplankton .

The food of roach, Rutilus rutilus (Actinopterygii: Cypriniformes: Cyprinidae), in a biomanipulated water supply reservoir

“…Our results, however, indicate that there are age differences, with one-year-old fish consuming mainly detritus and zooplankton and older fish showing a significant preference for detritus, macrophytes, and periphyton. Age differences have also been observed by Horppila (1994), who found that the importance of zooplankton decreased and that of benthos and plants increased, with increasing roach size. Similarly, Volta and Jepsen (2008) observed a clear age difference when comparing diet of in shallow and deep reservoirs, with young roach consuming mainly algae and older specimens consuming mainly zooplankton, detritus and macrozoobenthos.…”

Changes in roach (Rutilus rutilus (L.)) diet and growth in relation to river water quality

“…Comparing the composition of the diet with the structure of macroinvertebrate assemblages, roach feed on those macroinvertebrate taxa in the Žeimena River which are the most abundant. Contribution of different taxa to the diet changes together with the size of individuals, and this is in line with known general pattern (Horppila, 1994;Jamet et al, 1990). The overall diversity of food items in the diet of roach in the moderately polluted Mūša River is greater, but plant material forms a major part of the food and was consumed most frequently irrespective of the size of roach individuals, although abundance of many macroinvertebrate taxa on which roach feed is nearly twice greater than that in the Žeimena River.…”

“…According to Horppila (1994), the frequent use of plant food indicates a low availability of animal prey. But this cannot be an explanation in case of the Mūša River, where macroinvertebrate taxa are numerous and diverse.…”

“…It is known to be an opportunist species that can feed on zooplankton, benthic invertebrates, planktonic algae, epiphytes, macrophytes and detritus (Brabrand, 1985;Rask, 1989;Giles et al, 1990;Horppila, 1994;Specziar et al 1997); feeding behavior may vary in relation to the environment (Jamet et al, 1990).…”

Direct and indirect mechanisms behind successful biomanipulation

“…neither by external-nor sediment-derived phosphorus inputs (Kairesalo, et al, 1995;Hartikainen et al, 1996). This phosphorus increase, however, coincided with the early-summer migration of adult roach populations from the littoral areas to the pelagic zone (Peltonen & Horppila, 1992;Horppila 1994b). During 1989-93, these migrating fish, in particular, were the target of the trawlings which led to a dramatic reduction in their biomass; from 172 kg ha −1 (i.e.…”