Investigations into the effects of fish farming practices on water quality of some Transvaal rivers

D.Phil.The results of this investigation suggested that fish hatcheries may cause a deterioration in water quality of thereceiving stream. With regards trout hatcheries, two sources of pollution were distinguished. These were tenned normal or continuous hatchery effluent and secondly dam cleaning effluent. The former effluent was of little pollution consequence. The bacterial analyses indicated that faecal bacterial concentrations were largely determined by the concentration of these bacteria already present in the influent water. However, hatcheries can result in an increase in faecal bacterial concentrations downstream. Biological growth potential investigations suggested that both normal effluents and dam cleaning effluents were only slightly enriched in comparison with the influent conditions. Metabolizable nutrient addition to the effluent water was considered to be of little importance. Although the hatchery effluent from trout hatcheries may result in marked disturbances in the aquatic macro-invertebrate fauna, the organism community structures indicated that severe organic pollution was not occurring. The communities of the macro-invertebrates had become almost normalized within 300 m of the hatchery outfalls'. The water chemistry analyses confirmed the biological findings. The suspended material from both trout and carp hatcheries was the most important contributor to pollution. Recommendations included the use of the existing chemical and physical standards of the Water Act of 1956, however that these should be supplement~d by other biological parameters. A distance of 1 km should exist between a trout hatchery and a farm boundary unless effluent treatment is undertaken. Carp dam effluent may have to be treated depending on the water quality of the receiving stream