World Aquaculture - September 2023

32 SEPTEMBER 2023 • WORLD AQUACULTURE • WWW.WAS.ORG Pond management. Effective pond management was the key to nutrient distribution, facilitating concurrent effects of pond ecosystem functioning. Pond preparation, followed by manuring, was an essential step in sewage-fed fish farming. Each Bheri in EKW is renovated every 5 years to make it functional, or simply left to dry if siltation has not affected its productivity. For oxidation, bottom soil is tilled up to a depth of 8-12 cm after drying. Lime is applied at 500 kg/ha to increase pH and eradicate parasites and their cysts (Figure 4). Application of mahua oil cake at 2500 kg/ha follows liming to develop a suitable production environment, if necessary. Farming method. Usually, multi-stocking and multiharvesting was undertaken as a suitable method in EKW, considering its commercial importance and economic viability to farming communities. Intake of sewage took place in regular intervals at 2.5 percent of total volume of pond water, but varied depending on sewage availability. Water depth varied between 0.7 and 1.5 m. When pond water turned green, it was time to stock fish. Cultivable fish species were stocked several times a year, depending on the intensity of harvest operations as well as market demands. Fish were dipped in a potassium permanganate treatment before being released into sewage fed water to protect against infections. Composite fish culture was undertaken as an ideal practice of farming to harness the natural food web of the entire pond ecosystem. Fish culture strategy. The management strategy adopted in sewage-fed farms in EKW included (1) selection of species, (2) choice of species, (3) stocking density, (4) species size, (5) culture type, (6) species ratios, (7) harvest, and (8) depuration (Mandal et al. 2018). Selection of species was determined according to the feeding habits of various herbivores, carnivores, omnivores, and detrivores. Herbivores feeding on phytoplankton were the most efficient users of inputs. Detrivores fed on dead and decaying organisms, carnivores fed on small organisms including annelid larvae, insects, crustaceans and mollusks, and omnivores fed on both plants and animals. The diverse feeding habits of fish reared in sewage-fed farms allowed a strategic implementation FIGURE 4. A semi-dry sewage-fed ‘Bheri’ treated with lime in EKW. FIGURE 5. Fishermen dragging a net. FIGURE 6. Different fish species harvested from a sewage-fed ‘Bheri.’