Abstract
The present study was conducted to assess the impact of purposeful stocking of
common carp (Cyprinus carpio) on the species diversity of indigenous fish, their
yields, abundance and economic return in three beels named Korati (58 ha), Noli
(12 ha) and Proyag (62 ha) in three separate haors under Kishoregonj district
during April 2012 to March, 2014. Common carp fingerlings (average 2 cm) were
stocked at 2000 individual ha-¹ in Karati beel and Noli beel where Proyag beel was
treated as control beel without any stocking. Pertinent data were collected from
samples of fishers catch and fingerling stocking record. During investigation, a
total of 75 species of indigenous fish including 6 prawn species were recorded
from the control beel and 63-65 species from the treated beels belonging to 48
genera under 29 families. Shannon Weiner diversity index was calculated to be
3.083 in Korati, 3.144 in Noli and 3.178 in Proyag beel. In case of family wise fish
yields, Cyprinidae with an average of 545.31 kg ha-1 was the most dominant
family followed by Engraulidae with 136.07 kg ha¹ in the stocked beels. On the
contrary, Cyprinidae (241.19 kg ha-1) secured the top position followed by
Gobiidae (130.88 kg ha-1) and Bagridae (89.37 kg ha-1) in control beel. Among the
common fish guilds Barbs (274.44 kg ha-1) occupied the top position followed by
Carps (218.78 kg ha-1) and Catfishes (146.20kg ha-1) in the treated beels. On the
other hand, highest yield was exhibited by Catfishes (204.28 kg ha-1) followed by
Gobies (130.88 kg ha-1) and Barbs (130.08 kg ha-1) in control beel. Surface feeders
contributed thė bulk fish production of 572.36kg ha-¹ in stocked beels as opposed
to bottom feeders of 568.39 kg ha-¹ in control beel. Gadusia chapra was recorded to
obtain the highest yield in Korati (148.47 Kg ha-¹) and in Noli (123.66 Kg ha-1)
where Glossogobius guris occupied the highest position in control beel (139.88 Kg
ha-1). The highest catch was recorded in Korati beel (22.63%) in November, Noli
beel (21.26%) in October and Proyag beel (30.68%) in November. The mosquito net
occupied the top position in gear wise fish catch in Korari (33%) in Noli (27.76%)
and in Proyag beel (40.44%). Among the (IUCN, 2000) 54 threatened fish species,
27 species were present in control beel as opposed to 21 species in treated beels.
Average fish yield (1091.81 kg ha-1) was significantly higher in the stocked beels
than the control (871.26 kg ha-1) beel. Most of the bottom feeders were found to
have reduced yield in presence of common carp. Per hectare average profit was
BDT 1.365 Lac in stocked beels and BDT 1.120 Lac in control beel. Mean BCR value
was recorded to be 2.70 in stocked beels and 2.50 in control beel indicating the
economic profitability of common carp stocking in the beels of the haor area.