Abstract
Six experiments were done to examine the effects of inclusion of silver carp (Hypophthalmichthys molitrix)
on pond ecology and fish production in carp-SIS (small indigenous species of fish) polyculture and to assess
its socio-economic benefit from this type of rural aquaculture. Experiments Ist, 2nd and 4" were carried out in
the Field Laboratory Complex of the Faculty of Fisheries, Bangladesh Agricultural University (BAU), and
the 3rd 5th and 6th in Phulpur Upazila of Mymensingh district from 2004 to 2006. The first trial was
conducted to evaluate the impact of addition of silver carp on SIS (mola, Amblypharyngodon mola and punti,
Puntius sophore) in carp-SIS polyculture when bottom feeder was common carp (Cyprinus carpio) or mrigal
(Cirrhinus cirrhosus). The experiment had 4 treatments with 4 replications each. In all the treatments 10,000
punti, 10,000 mola and 8,000 bottom feeder/ha were stocked. The addition of silver carp in mrigal ponds
showed a negative effect on both adult SIS, while common carp ponds showed a weaker negative effect on
mola and a positive effect on punti. Common carp was not affected by silver carp but yield of mrigal
decreased by 39% while total yield was increased by 20% in common carp ponds. The second trial was
conducted to test the effects of silver carp and of each SIS on the growth, survival and yield of the large and
small fish and on pond ecology. The experiment had 6 treatments with three replications per treatment. In all
the treatments, 3,300 rohu, 3,300 catla and 3,300 common carp/ha were stocked. Silver carp 1,000 and/or SIS
25,000 (mola/punti)/ha were added to the appropriate treatments. The addition of silver carp did not affect
punti and mola reproduction severely but negatively affected rohu and catla growth and yield by 20-25%. It
also did not affect common carp yield while reduced punti yield by 10% and mola yield by 50% but silver
carp's own biomass increased total yield by 20%. The addition of 250 mola or 250 punti did not affect the
yield of any of the large carps. In third experiment, effects of silver carp and the SIS mola and/or punti on
fish polyculture production and pond ecology were studied. The trial had 8 treatments with 5 replications
each. In all the treatments, 3,300 rohu, 3,300 catla and 3,300 common carp/ha were stocked. Silver carp
1,000 and/or SIS 25,000 (either all mola, all punti, or half of each one)/ha were added to the appropriate
treatments. The addition of silver carp decreased rohu and catla yields by 45-50%, did not affect punti and
mola reproduction severely but reduced the yields by 25% and 35%, respectively while increased silver carp
yield by 12%. The fourth and fifth trials were conducted to reduce the negative effect of silver carp on other
carps and to increase total yield and income due to its stocking. Fourth trial had 6 treatments with 3
replications, in which 300-500 silver carp/ha was added or partially substituted major carps when bottom
feeder was the common carp. In fifth trial, there was 8 treatments with 5 replications each, in which 500/ha
silver carp was added or substituted the same number of major carps when bottom feeder was either common
carp or mrigal. In both the cases, the stocking density was 10,000 carps (rohu, catla and either common carp
or mrigal, at 1:1:1 ratio) and 25,000 SIS/ha. The 300/ha silver carp can be considered to be a "no effect"
stocking density, while 500/ha and 1,000/ha silver carp might be preferred by farmers to keep the option of
selling or consuming the silver carp. The sixth study was conducted to assess the nutritional and socioeconomic benefits of introduction of carp-SIS polyculture technology in rural households belonging to two
groups viz. fish farming households and non-fish farming households. The consumption of large and small
fish was found to increase significantly (P<0.05) among the fish farming households than the non-fish
farming households. Implementation of the carp-SIS polyculture technology increased large carp production
104%, SIS 292% and total yield 109% in their ponds while income increased from aquaculture by 205% and
total income 210%. Women participation was visible in carp-SIS aquaculture activities without compromising
with other households works.