A test of a model for planktivorous filter feeding by bream Abramis brama

Synopsis The planktivorous feeding of bream, Abramis brama on Daphnia hyalina and Bosmina coregoni was analyzed in a stepwise regression analysis with the average size (and standard deviation) of consumed organisms as dependent variable and the size of the fish, the average size (and standard deviation) of the organisms and their density in the environment as independent variables. Three basic predictions on filter feeding were formulated and tested. It was predicted that the (average) prey size should increase with fish size, but that the standard deviation should decline. Secondly the prey size should be strongly correlated with the prey size available and thirdly the prey density should have little effect on the size selection. These hypotheses could not be rejected for bream>10 cm feeding on B. coregoni and for bream>20 cm feeding on D. hyalina. The hypotheses were not valid for smaller bream as these acted as particulate or combined filter- and particulate feeders.     

The algal periodicity in Tjeukemeer during 1968–1978

The seasonal periodicity of algal numbers and biomass and of chlorophyll-a was investigated in the shallow, eutrophic, alkaline and peaty lake, Tjeukemeer, The Netherlands, during 1968–1978. Diatoms and Scenedesmus spp. were abundant throughout the whole period.Several blue-green algal species, occurring since 1971, usually dominated for most of the year. Relative abundance of algal species in Tjeukemeer during the study period were compared with that in 1955–1960.