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The production performances of giant freshwater prawn Macrobrachium rosenbergii and Nile tilapia Oreochromis niloticus in C/N-controlled periphyton-based polyculture systems were evaluated in triplicate. Three different management practices were compared: the traditional practice without addition of periphyton substrates and carbohydrate (Control), addition of maize flour to maintain a carbon: nitrogen rate of 20:1 (treatment CN) and addition of both maize flour and periphyton substrates (treatment CN+P). This experiment used a pre-optimized stocking density of tilapia and freshwater prawn by Asaduzzaman et al. Aquaculture [286 (2009) 72]. All ponds were stocked with prawn (3 m2) and monosex Nile tilapia (1 m−2). Bamboo side shoots were posted vertically into the pond bottoms as periphyton substrate covering an additional area of 171 m2 for periphyton development. A locally formulated and prepared feed containing 17% crude protein with C/N ratio close to 15:1 was applied twice daily in all ponds considering the body weight of freshwater prawn only. Water quality parameters, except total alkalinity did not vary significantly ( P > 0.05) among treatments. Both, organic matter and total heterotrophic bacterial loads ( THB) in the sediment were significantly (P < 0.05 ) higher in treatment CN+P followed by treatment CN and control. Periphyton biomass in terms of dry matter and chlorophyll a values constantly decreased during the culture period. Substrates contributed 66% and 102% higher net yield of freshwater prawn than CN and control treatment respectively. [ABSTRACT FROM AUTHOR]

A polyculture experiment with the large carp rohu, Labeo rohita (Hamilton), carla, Catla catla (Hamilton) and either mrigal, Cirrhinus mrigala (Hamilton) or common carp, Cyprinus carpio (L.) (as cash crop fish), and the small indigenous fish punti, Puntius sophore (Hamilton) (as food for the small-scale farmer family) was carried out at the Field Laboratory of the Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh. The main objective was to compare polycultures of large carp in which the bottom feeder is either the native mrigal or the exotic common carp. Secondary objectives were to assess the effects of adding the small indigenous species punti to polycultures of large carp, and to compare the effects of mrigal and common carp on punti production and reproduction. It was found that (i) common carp damaged embankments, had no effect on carla, improved rohu performance by 50% and total fish production by 20%; (ii) punti addition did not affect rohu, catla and total yield, improved mrigal performance by 50%, and decreased common carp performance by 20%; and (iii) punti was not affected either by common carp or by mrigal. However, its performance was not satisfactory, probably owing to frequent netting, which might have hindered growth and breeding. In spite of the embankment damage caused by common carp, this bottom feeder seems to be more promising than mrigal, because it leads to higher fish production. The addition of punti to the large carp polyculture is a viable proposition, as it does not reduce cash crop production, and might be a good food source for a small-scale farmer's family. [ABSTRACT FROM AUTHOR]