The Growth and Mortality of Four Species of Fish in the River Thames at Reading

This paper results from a series of observations made on fish populations in the River Thames at Reading between October 1958 and October 1959. The work forms part of a long-term ecological investigation being carried out in the Caversham-Sonning reach of the river. The four species being discussed in this paper are roach-Rutilus rutilus (L.), bleak-Alburnus alburnus (L.), dace-Leuciscus leuciscus (L.) and perch-Perca fluviatilis L. These four species comprised 91 %Y of the total catch and estimates of their population densities have been reported (Williams 1965). The stock densities recorded were extremely high and the present study on growth and mortality is a necessary step in the evaluation of both the interrelationships within the community and those between the community and its environment. Very few population studies have been made of coarse fish in Britain, especially from rivers. For some species, however, there are published data on growth in various habitats which may serve to indicate whether or not the Thames fish are stunted. Only for perch is there comparable work on both growth and mortality in another habitat (Le Cren 1958).