Page 48 - World Aquaculture Magazine - March 2011

46 March 2011
be insufficient to provide an ade-
quate means of livelihood. Thus,
char dwellers are involved in
secondary occupations. Accord-
ing to the survey, all respondents
reported that dead-river fish cul-
ture was their secondary occu-
pation. The majority of respon-
dents (70 percent) were involved
with fish production in dead-riv-
ers for income generation, while
27 percent did so for household
consumption. The proportion
of respondents needing to learn
fish culture technology was only
three percent.
Dead-river Aquaculture
The peak season of dead-river fish
culture was from October to March.
Fish fingerlings were stocked in Oc-
tober and harvested primarily in
March, a culture period of around
six months. A range of hatchery and/
or nursery produced fish species were
cultured in the Holholia dead-river.
The selection of fish species depended
on availability. Fish farming groups
mainly stocked Indian major carp
including catla (Catla catla), rohu
(Labeo rohita ), mrigal (Cirrhina cir-
rhosus) and exotic carp such as big-
head carp (Aristichthys nobilis ), com-
mon carp ( Cyprinus carpio), grass
carp (Ctenopharyngodon idella), and
silver carp ( Hypophthalmichthys
molitrix). They also stocked silver
barb (Barbodes gonionatus) and Nile
tilapia ( Oreochromis niloticus). How-
Table 1. Salient features of the Holholia dead-river
fish culture in 2008.
Feature Value
Total area (ha) 4.45
Group members 70
Fish culture season November - March
Stocking rate (fingerlings/ha) 2,505
Productivity (kg/ha) 972
Production costs (PC) (US$/ha) 160
Gross revenue (GR) (US$/ha) 992
Net return (GR-PC) (US$/ha) 832
Net return for a group member (US$/ha) 12
Total net return for a group member (US$/4.45ha) 53
Harvesting of fish by a group of fishers.
Small indigenous fish are also captured with cultured
fish.
ever, many respondents reported that
they avoided grass carp because the
species consumed and uprooted rice
plants. Many char dwellers culture
rice on the shore of the river. In gen-
eral, group members do not attempt
to stock any specific ratio of fish spe-
cies. The stocking density of fish fin-
gerlings was reported to be 2,505 per
ha in 2008. The average size of finger-
lings stocked varied between 7 and 12
cm. Male members of fish farming
groups usually procured fingerlings
and women were involved in stocking
with the help of men.
Dead-river fish culture is an ex-
tensive aquaculture system that pri-
marily relies on natural food (phyto-
plankton, zooplankton, periphyton
and benthos). As such, no feed or fer-
tilizer were applied in dead-river fish
culture. According to respon-
dents, dead-river fish farming
required significant labor input
to strengthen bamboo fencing
to prevent the escape of stocked
fish, as well as entry of preda-
tory fish. Labor is also required
for fish harvesting. Partial har-
vesting of larger fish (700-1,200
g) is practiced, allowing smaller
fish to grow. A total of 20 partial
harvests were conducted during
the fish harvesting season. Fish
harvesting itself is a specialized
service where 7-10 professional
fishers usually harvest fish using
seines. Harvested fish are kept in
plastic or aluminum containers
containing river water until they are
sold to the market.
A number of interdependent fac-
tors affected growth rates and pro-
ductivity of fish in dead-river culture,
including environmental factors,
stocking and survival rates, fingerling
quality, water quality and other as-
pects of river management. The size
of fish at stocking, the duration of
culture and the size at which the fish
were harvested also influenced total
yield. Farming groups stocked larger
fingerlings which could have had a
positive effect on survival and growth
as well as yield. The total yield of fish
reported by respondents was 972 kg/
ha in 2008 (Table 1). It was difficult to
estimate the amount of stocked fish
harvested but it was suggested by re-
spondents that stocked fish account-