| Research on practices for improving water quality in channel catfish Ictalurus punctatus ponds was conducted at the Auburn University Fisheries Research Station, Auburn, Alabama, in 1998 and 1999. The objective of this two-year study was to determine better management practices to enhance water quality and improve production efficiency. In the first year, oxidation of bottom soil by drying, tilling, and applying sodium nitrate was performed (dry-till and dry-till with sodium nitrate treatments). The second year, based on the results obtained during the first year, precipitation of phosphorus (P) from water by applying gypsum was compared to the dry-till treatment (dry-till and dry-till with gypsum treatments). Control ponds were not subjected to bottom drying, tilling, sodium nitrate, or gypsum treatment. Channel catfish fingerings were stocked at 15,000/ha.; In the first year, water in ponds from dry-till and dry-till with sodium nitrate treatments had lower concentrations (P < 0.01) of soluble reactive P, nitrate (NO3−) and nitrite (NO2−) nitrogen (N), total ammonia (NH3) nitrogen, total suspended solids and turbidity, and higher values of pH, Secchi disk visibility, total alkalinity, total hardness, and calcium (Ca2+) hardness than water in control ponds. Ponds of the dry-till treatment also had lower concentrations (P < 0.01) of total P and total N than control ponds. Total fish production and survival rate did not differ among the treatments (P > 0.05). The findings suggested that drying and tilling pond bottoms between crops could achieve water quality improvement. Applying sodium nitrate to dry, tilled pond bottoms did not provide water quality improvement.; In the second year, the treatment with the best results from the first year, dry-till, was compared with a dry-till with gypsum treatment. Enough gypsum was applied to give a total hardness of about 200 mg/L, and gypsum was reapplied as needed to maintain the hardness. Compared to the control, dry-till and dry-till with gypsum treatments had lower concentrations ( P < 0.01) of total and soluble reactive P, total N, and total NH3-N, and higher concentrations (P < 0.01) of dissolved oxygen. Ponds of the dry-till with gypsum treatment also had lower concentrations (P < 0.01) of chlorophyll a&barbelow;, chemical oxygen demand, and total alkalinity than the control. Total fish production and survival rate did not differ ( P > 0.05) among the treatments. These findings suggest that drying and tilling pond bottoms between crops and treating low hardness waters with gypsum could achieve water quality improvement. |
