Eco-Biology of CIRRHINUS REBA (HAMILTON) with Special Reference to Its Fishery at Rajshahi

Abstract

The eco-biology and fishery of Cirrhinus reba in Padma river were studied for a period of 3 years (January 2014 to December 2016) in 5 different sampling stations (Godagari, Bullanpara, Padma garden, Yusufpur and Charghat). In experiment 1, the study focused on physico-chemical parameters and their relation with occurrence and abundance of plankton population in Padma river. The physico-chemical condition and plankton population of Padma river exhibited more or less variations according to the change of months and season. The study revealed that monsoon rain and land drainage seems to play an important role in changing the physico-chemical parameters of the Padma river. During the study period, a total of 130 species of phytoplankton and 30 species of zooplankton were recorded. The findings of the present study indicate that the ecology of Padma river are still in good condition for C. reba. In experiment 2, Length-weight frequency distribution of C. reba ranged between 6.60 to 23.80 cm in total length and 2.63 to 136.00 g in total body weight during the sampling period. The ‘b’ value for male, female and combined sex was 3.020, 3.215 and 3.116 respectively, that indicates isometric growth type in male and positive allometric growth type in female and combined sexes. The minimum and maximum value of KF during the study period was 0.39 and 1.65 for male and 0.48 and 1.83 in females with mean value of 0.94 and 0.97 for combined sex. Spearman rank correlation showed that KF was significantly correlated with both total length (p = 0.125) and body weight (p = 0.324) of C. reba. In experiment 3, based on the finding of the study, C. reba is considered to have herbivorous feeding habits. The major food items of analyzed gut content of C. reba was detritus and plant materials. Small fishes are exclusively zooplankton feeders subsisting mainly on small rotifer, cladocera, copepoda and crustacean, whereas the adult ones are plankton and detritus feeder. The feeding activity of this fish species fluctuated between seasons and length groups. The conducting the relationship between total length and alimentary canal of this species an equation of ACL = - 0.923+1.8023(TL) was found and the ratio obtained was 1:3.07, which indicates herbivorous nature of C. reba. In experiment 4, during the study period, reproductive activity of C. reba was analyzed in terms of sex ratio, spawning season and fecundity. In the present study, 600 species were collected among them 317 was male and 283 was female, with a sex ratio of 1:0.89. There were differences in the monthly male, female number and sex ratio, which indicates unequal distribution of male and female fishes with number of female fishes increases during spawning season. However, the overall sex ratio was also did not differ significantly from the expected value of 1:1 (df = 1, χ2 = 3.84, p<0.05). Values of GSI and GLI also fluctuated with months and number of gravid females was highest (70 %) in the month of August, which indicates peak breeding season of this fish species is August. The total number of mature eggs varied from 11542.10 to 265042.23 with mean value 11542.10 ± 53602.28. The results of the linear relationship depicted that fecundity increased at the rate of 5.892, 1.492 and 1.316 times of the total length, weight of fish and weight of ovary, respectively. In experiment 5, although the fishery of C. reba constitute a minor portion of Padma river’s total catch, it forms a economically important role in fishery status of Padma river. The major fishing gears operated for capturing of C. reba were cast net (Jhaki jal), Gill net (Current jal), Square lift net (Tar jal), Seine net (Ber jal). The average yearly landings of C. reba was 3618 kg, which was low but contributes significantly in fishery of Padma river. The highest landing of this fish was in the month of November. During monsoon months, the catch was low due to the high water level of river that decreases the catching capacity of fishing gears. But after July, the quantity of landing gradually increased since the juveniles attained the adulthood and started gaining the maximum size and the water level of river gradually becomes low, which make the fishes available in fishing gears. Study of different aspects of the ecology, biology and fishery of C. reba indicates the suitability of this species for culture in both the ponds and other aquaculture systems.