Seasonal dynamics of food consumption, growth and production of 0+ fish and their impact on zooplankton in a reservoir with trophic gradient

Project No. 206/06/P418

Applicant: MSc. Mojmír Vašek, PhD.

Financial support: Czech Science Foundation

Duration: 2006-2008

Deep-valley reservoirs are unique aquatic ecosystems characterized by a high degree of spatial and temporal variability. This project aimed to analyze how variable environmental conditions within a model reservoir influence seasonal dynamics of age-0 fish abundance, food consumption, growth and production. Dynamics of age-0 fish was studied in the Římov Reservoir during two subsequent years, 2006 and 2007, that differed markedly in hydrological and weather regimes. A few generalist species from two families, Percidae and Cyprinidae, dominated age-0 fish assemblages. At the start of growing season, percids were abundant in pelagic habitat, but later on they shifted to littoral zone. An opposite trend in habitat use was recorded for age-0 cyprinids. Flooded shoreline vegetation enhanced survival of age-0 fish in 2006, while increased spring temperatures in 2007 accelerated ontogenetic development of age-0 fish. Underyearling fish in the Římov Reservoir were largely planktivorous throughout the whole growing season of both years. In the pelagic zone of the reservoir, impact of age-0 fish on zooplankton of the genus Daphnia was quantified using bioenergetics modelling. The estimated consumption rates of age-0 fish assemblages were found too low to be responsible for the midsummer decline of Daphnia population. In summary, extensive data on abundance, distribution, growth, production and food consumption of age-0 fish were collated during this project. The data provided valuable information on the structure and functioning of a reservoir ecosystem and, in practice, they can be beneficial for management of fisheries and water resources.