La vision classique des limnologistes fut de considerer les interactions entre les composants des Ccosystemes lacustres comme un flux d'influence unidirectionnel des sels nutritifs vers le phytoplancton, le zooplancton, et finalement les poissons, par l'intermediaire de processus de controle successivement physiques, chimiques, puis biologiques (StraSkraba, 1967). L'effet exerce par les poissons planctophages sur les communautes zoo-et phytoplanctoniques ne fut reconnu qu'a'partir des travaux de HrbaEek et al. (1961), HrbaEek (1962, Brooks & Dodson (1965), et Stras'kraba (1965. Ces auteurs montrerent (1) que dans les Ctangs et lacs en presence de poissons planctophages predateurs visuels, les communautes zooplanctoniques etaient composees d'especes de plus petites tailles que celles presentes dans les milieux depourvus de planctophages et, (2) que les communautes zooplanctoniques resultantes, composees d'especes de petites tailles, influencaient les communautes phytoplanctoniques.Bien que la variabilite de la reponse du phytoplancton a la predation par les poissons revele l'importance d'autres facteurs (tels que la limitation en sels nutritifs et la competition interspecifique des algues), ces travaux demontrerent que les communautes zoo-et phytoplanctoniques pouvaient effectivement Ctre affectees par l'alimentation selective des poissons planctophages. Pendant les deux dernieres decennies, de nombreux travaux en limnologie se sont concentres sur cet impact radical des poissons sur les communautes planctoniques. La reponse directe des communautes zooplanctoniques a la predation visuelie des poissons planctophages (appeles en anglais 'particulate feeders') a suscite un interst tout particulier, alors que les effets multiniveaux causes par les poissons planctophages filtreurs (predation sur le zooplancton plus broutage du phytoplancton) ont CtC plus rarement abordb. Les objectifs de cette revision sont de documenter les inter-relations poissons-plancton, afin (1) d'obtenir des elements d'appreciation de l'impact des poissons sur les communautts planctoniques, et (2) d'etablir des modeles mecanistiques d'alimentation planctophage tenant compte du repertoire alimentaire et de la selectivite du poisson, des reponses adaptatives du plancton, et des conditions du milieu.L'approche utilisee ici est basee sur des resultats experimentaux de terrain et de laboratoire provenant de la litterature concernant les systemes tropicaux et temper& d'eau deuce (parfois marine). Quatre groupes de poissons planctophages sont distingub: les pmdateurs visuels limit& par la taille de leur bouche (c'est-a-dire les larves et les especes de petites tailles: 'gape-limited predators'), les predateurs visuels proprement dit ('particulate feeders'), les filtreurs par pompage ('pump filter feeders'), et les filtreurs par deplacement ('tow-net 98 filter feeders'). Pour chaque groupe, les mecanismes de selection des proies sont analyses, aussi bien du point de vue du predateur que de la proie. Afin de rechercher les mecanismes determinant la select...

Fish play a key role in the trophic dynamics of lakes, not least in shallow systems. With climate warming, complex changes in fish community structure may be expected owing to the direct and indirect effects of temperature, and indirect effects of eutrophication, water-level changes and salinisation on fish metabolism, biotic interactions and geographical distribution. We review published and new data supporting the hypotheses that, with a warming climate, there will be changes in: fish community structure (e.g. higher or lower richness depending on local conditions); life history traits (e.g. smaller body size, shorter life span, earlier and less synchronised reproduction); feeding mode (i.e. increased omnivory and herbivory); behaviour (i.e. stronger association with littoral areas and a greater proportion of benthivores); and winter survival. All these changes imply higher predation on zooplankton and macroinvertebrates with increasing temperatures, suggesting that the changes in the fish communities partly resemble, and may intensify, the effects triggered by eutrophication. Modulating factors identified in cold and temperate systems, such as the presence of submerged plants and winter ice cover, seem to be weaker or non-existent in warm(ing) lakes. Consequently, in the future lower nutrient thresholds may be needed to obtain clear-water conditions and good ecological status in the future in currently cold or temperate lakes. Although examples are still scarce and more research is needed, we foresee biomanipulation to be a less successful restoration tool in warm(ing) lakes without a strong reduction of the nutrient load.

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SUMMARY 1. We examined whether a large stock of tilapia (>750 kg ha−1, in littoral areas >1300 kg ha−1), mostly Oreochromis niloticus (L.) and Tilapia rendalli (Boulenger), could contribute to the eutrophication of a tropical reservoir (Lago Paranoá, Brasília, Brazil) by enhancing P‐loading. 2. We took advantage of an extensive fish kill (>150 tons removed) during May–August 1997 in a hypereutrophic branch of the reservoir to compare water quality characteristics 1 year before and after this event by means of BACI statistics. We also measured P‐excretion rates in laboratory trials to assess the P‐loading of the reservoir by the tilapia relative to tributary inputs and loading from a sewage treatment plant. 3. Concentrations of chlorophyll a (decline from 84 to 56 μg L−1, P=0.018) and total P (decline from 100 to 66 μg L−1, P < 0.001) decreased significantly in the branch of the reservoir affected by the fish kill, compared with a similar but unaffected branch that served as a control. Because P‐loading by both a sewage treatment plant and tributaries remained high after the incidence, the fish kill was likely to contribute to the observed water quality improvement. 4. Removing 150 tons of dead tilapia corresponded to 20 days of external total phosphorus load (TP‐load) to the branch, and resulted in a reduction of 5.1 kg P day−1 in internal recycling via tilapia excretion, which is equivalent to 12% of the external TP‐load. 5. Implementing professional tilapia cast‐net fisheries could be an efficient biomanipulation approach to improve water quality and limit the occurrence of cyanobacteria blooms and fish kills in hypereutrophic branches of Lago Paranoá and similar tropical lakes.

SUMMARY 1. In a comparative study, we examined the potential for fish to structure planktonic food webs in shallow mesotrophic to hypereutrophic Northeast Brazilian reservoirs. The food webs were dominated by three guilds of fish (facultative piscivores, generalist planktivores and omnivores), small herbivorous zooplankton and bloom‐forming cyanobacteria, with few littoral macrophytes. 2. A principal component's analysis on data from 13 reservoirs (27 sampling dates in 1995–99) revealed that euphotic depth, the relative density of phytoplankton (i.e. the percentage of overall phytoplankton density) represented by cyanobacteria, and the relative biomass of fish (i.e. percentage of overall biomass) represented by omnivores and facultative piscivores, explained most of the variance in the data. Physico‐chemical conditions, lake morphometry and rainfall were secondary factors. 3. Phytoplankton was related to fish guild structure. Chlorophyll concentration increased with total phosphorus and the relative biomass of omnivorous fish, decreased with the relative biomass of facultative piscivores, but was unrelated to the biomass and mean body size of herbivorous zooplankton. Chlorophyll concentration and the densities of filamentous and colonial cyanobacteria decreased with the ratio of the biomass of facultative piscivores to that of omnivores (FP : OM). 4. We propose two complementary mechanisms for the observed relationships between fish and phytoplankton. At a low biomass of facultative piscivores, juvenile zooplanktivorous fishes may induce a trophic cascade on zooplankton in the littoral zone. Regardless of piscivore biomass, piscivores and omnivores may regulate phytoplankton via multichannel omnivory because of the predominance of omnivorous or detritivorous foraging behaviour. 5. Manipulative experiments are needed to explore further whether, depending on priorities in the use of the reservoir, fisheries management could alter the FP : OM ratio either to enhance fish yields or to reduce phytoplankton densities and cyanobacterial blooms.

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We quantified the effects sf planktivore biomass and planktivore type in an experimental messcosm study sf factorial design in which five levels of fish biomass (0-75 @m3) were cross-classified with two plantivore types: filter-feeding gizzard shad (Dorossrna cepedianurn) and visual-feeding bluegill (Lepomis macrochirus). As fish biomass increased, cladocerans, cyclopoids, particulate phosphorus (PP) >200 pm, and chirsnomids declined; conversely, rotifers, primary productivity, chlorophyll a, turbidity, unicellular flagellates, colonial and unicellular green algae, pennate diatoms, total phosphorus, and 20-200 and 12-20 p m PP were enhanced. In the presence of gizzard shad, as compared with bluegill, cyclspoids, turbidity, unicellular green algae, pennate diatoms, >200 pm PP, and chironomid tubes were higher whereas colonial green algae and c0.2 pm PP were lower. Fish biomass operated independently of planktivore type for most variables, except copepods, colonial green algae, turbidity, and 20-200 krn PP. Although gizzard shad and bluegill have different trophic cascade pathways, fish biomass was more important than planktivore type as a regulator of plankton communities and water quality. planktivore biomass md plankton biomass appear to be nonlin-