Optimization of stocking ratios of two Indian major carps, rohu (Labeo rohita Ham.) and catla (Catla catla Ham.) in a periphyton-based aquaculture system

Production of combinations of rohu (Labeo rohita) and catla (Catla catla) f rom periphyton-based aquaculture system was compared using 12 ponds and six stocking ratios: 100% rohu alone (treatment 100R), 80% rohu plus 20% catla . (80R/20C), 60% rohu plus 40% catla (60R/40C), 40% rohu plus 60% catla (40 R/60C), 20% rohu plus 80% catla (20R/80C) and 100% catla alone (100C). Pond s (75 m(2), depth 1.5 in) were stocked at a rate of 15 000 fingerlings ha(- 1). Bamboo poles (mean length = 2.0 m; mean diameter 5.5 cm; 9 poles m(-2)) used as periphyton substrates were planted vertically into the pond bottom s and ponds were fertilized fortnightly with cow manure, urea and triple su per phosphate (TSP) at rates of 4500, 150 and 150 kg ha(-1), respectively. Phytoplankton biomass decreased with increasing catla biomass whereas perip hyton biomass decreased with increasing biomass of rohu. Ash content of per iphyton increased with increasing number of catla and decreasing number of rohu. Growth of catla was dependent (P less than or equal to 0.05) on stock ing density but that of rohu was independent (P > 0.05) of stocking density , possibly because of the reliance of the latter on periphyton for food. Hi ghest fish yield was recorded in treatment 60R/40C (586 kg ha(-1)), followe d by treatments 40R/60C (459 kg ha(-1)), 80R/20C (439 kg ha(-1)), 20R/80C a nd 100R (both 225 kg ha(-1)),and 100C (146 kg ha(-1)), respectively, over t he 70-day period. A stocking ratio of 60% rohu and 40% catla appears approp riate for periphyton-based production systems of Indian major carps, althou gh the ratio is likely to be influenced by both stocking density and food s upply. (C) 2001 Elsevier Science B.V. All rights reserved.