The lsraeli Joumal of Aquaculture - Bamidgeh 51(2), 1999, 47-57
EFFECTS OF FEED PROTEIN CONCENTRATION
AND FEEDING RATE COMBINATIONS ON QUALITY OF POND
WATER AND EFFLUENT IN CHANNEL CATFISH CULTURE
Amit Gross, Claude E. Boyd and R. T. Lovell
Department of Fisheries and Allied Aquacultures, Auburn University, Alabama 36849, USA
(Received 30.11.98, Accepted 22.4.99)
Three feeds with different concentrations of crude protein were applied to 400 m² channel catfish ponds at the Auburn University Fisheries Research Unit. Fish were fed to satiation with the 26% crude protein feed; the other two diets (32% and 36% crude protein) were applied in amounts calculated to provide the same crude protein input as for the 28% crude protein diet treatment. Using this practice, feed application decreased as feed crude protein increased; likewise, phosphorus and organic matter loads to the ponds decreased.
The feeding practice and diets used in this study had no measurable effects on nitrogen concentrations in pond waters and effluents or on fish production. Despite the smaller phosphorus inputs with 32% and 36% protein feed, only a small fraction of the applied phosphorus remained in the water column. The differences in phosphorus input among treatments did not affect phosphorus concentrations in pond water or effluents. When fishponds were drained for harvest, the quality of the effluent did not change until about 75% of the water had been released. The water quality in the effluents then deteriorated because the pond bottom was disturbed by the outflowing water, fish activity and harvest. By holding the last 25% of the water in the ponds for 12-24 h after fish harvest, much of the suspended matter was removed by sedimentation. The water can then be released slowly to prevent resuspension of the sediment and obtain a better quality effluent.