A catch‐effort method of estimating fish density and biomass using three small seine nets placed simultaneoulsy to enclose a known area of water is described. The efficiency of capture in the first catch was high for both density and biomass with an overall average of 70 and 69% respectively, and 95% confidence limits of approximately 20% for both.

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1. The production of three-spined sticklebacks, Gastero.steus aculeatus, estimated in the margin of a large cbannelized lowland river, averaged 42.3 g m"^ yr~' and the P/B ratio was 3.7. The production value greatly exceeds those previously recorded for G. aculeatus and results from tbe very high population densities.2. Life-bistory tactics of tbe sticklebacks included both r-and K-selected traits.3. Tbe fish were carnivorous in tbe summer months but predominantly detritivorous in the winter.

Following the implementation of an experimental habitat improvement programme in the River Perry, a small lowland river in Shropshire, using low dams, current deflectors and artificial cover structures, marked changes in fish distribution and abundance were recorded in some study sections which appeared to be related to the effects of the improvement structures in recreating natural river features such as the pool‐riffle pattern. Over the site as a whole, the population densities of dace and chub increased from means of 325 fish ha−1 and 229 fish ha−1 in the year before habitat improvement to means of 568 fish ha−1 and 313 fish ha−1 in the year following habitat improvement, increases of 75 and 37% respectively. Similarly, standing crops of dace and chub increased from pre‐improvement means of 19.7 kg ha−1 and 66.6 kg ha−5 to post‐improvement means of 25.8 kg ha−1 and 83.0 kg ha−1, increases of 31 and 25% respectively. Distribution mapping studies revealed considerable fish relocation following habitat improvement, with large concentrations of fish being recorded in the vicinity of the improvement structures. It is concluded that the improvement programme was successful in partially mitigating the adverse effects on the fishery of previous land drainage river channel works.

The contents of the stomachs of 38 rainbow trout stocked in Llyn Alaw, Anglesey, in August 1969 and caught between October 1969 and February 1970 were analysed. The fish were actively feeding on the bottom fauna throughout the winter and 21 of the stomachs were full or distended. The mean volume of the contents of the stomachs was 2–8 times greater than that of the contents of stomachs of similarly sized brown trout caught at the same time.