Rice-fish culture: feeding, growth and yield of two size classes of Puntius gonionotus Bleeker and Oreochromis spp. in Bangladesh

Concurrent rice-fish culture experiments were conducted in Bangladesh to compare and evaluate the feeding, growth, condition factor, survival and yields of two sizes of silver barb (Puntius gonionotus) and tilapia (Oreochromis spp.) in 1994 and 1995, respectively, and to compare paddy yield and ecological conditions between rice-fish and rice-alone situations. Survival, specific growth rate, condition factor and yields were better with the small-sized (5.6-6.1 cm) P. gonionotus than the larger-sized (8.8-9.6 cm) P. gonionotus and either sizes (4.0-7.5 and 9.5-14.7 cm) of Oreochromis spp. P. gonionotus was found to be a macrophy-tophagous column feeder with benthic foraging habit on tiny molluscs. There was clear evidence of its foraging on paddy grains. Conversely, Oreochromis spp. was found to be a detritivorous browser or surface grazer. Ontogenetic shifts in diet were pronounced in P. gonionotus while absent in Oreochromis spp. Best mean net fish yield was 271.03 kg ha(-1) crop(-1) with small P. gonionotus in 78 days culture, significantly higher than with Oreochromis spp. (P < 0.05). Paddy yields were 1.5-3.7 t ha(-1) crop(-1) in rice-fish and 1.5-1.8 t ha(-1) crop(-1) in rice-alone culture with insignificant differences between the years (P > 0.05). Water quality parameters were, in general, within the acceptable range for aquaculture. Small sizes of P. gonionotus should be preferred over the Oreochromis spp. for the integration of rice-fish nursery systems but further work should be done on the dietary importance of rice grains to P. gonionotus. (C) 1997 Elsevier Science B.V.