No abstract

The impact of a common brown trout farm on water quality was investigated at a site well flushed by lapping and tidal current. Dissolved oxygen, suspended matter, phosphate, nitrite and nitrate were seemingly not affected by the farm. High concentrations of ammonia were clearly observed close to the raft, but rapidly vanished a short distance from it, when the fish biomass was at least 576 tonnes. At that time the nitrogen loadings from the farm were estimated at 101 kg/day. On the site, phytoplankton was similar to that of the nearby French coastal area of the English Channel, concerning generic composition (extensively dominated by diatoms) and the seasonal succession of genera. The farm did not cause any increase of faecal coliform bacteria. At this stock level, the dispersal characteristics of the farm site greatly reduced its apparent impact on the water quality.

An environmental monitoring study was carried out between 1993, 1995 on the site of a marine trout farm located in the Bay of Cherbourg (English Channel), France. The study dealt with the sea bottom and solid waste from the farm, and concerns the deposition rate, sediment analysis and chemistry (fine fraction < 63 μm, organic matter, carbon, nitrogen and trace metals such as Cu and Zn), bottom oxygen demand, benthic macrofauna, and underwater video surveying. The observed impact was very moderate and localised, and showed no real abnormality. This was mainly due to the strong hydrodynamics characterising the site. A separate phase of the same study dealt with dissolved waste and the water mass (Part One: Current and water quality).

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