This study evaluates changes in fish species diversity over time in Hakaluki Haor, an ecologically critical wetland in Bangladesh, and the factors affecting this diversity. Fish species diversity data were collected from fishers using participatory rural appraisal tools and the change in the fish species diversity was determined using Shannon-Wiener, Margalef's Richness and Pielou's Evenness indices. Principal component analysis (PCA) was conducted with a dataset of 150 fishers survey to characterize the major factors responsible for the reduction of fish species diversity. Out of 63 fish species, 83% of them were under the available category in 2008 which decreased to 51% in 2018. Fish species diversity indices for all 12 taxonomic orders in 2008 declined remarkably in 2018. The first PCA (climatic change) responsible for the reduced fish species diversity explained 24.05% of the variance and consisted of erratic rainfall (positive correlation coefficient 0.680), heavy rainfall (À0.544), temperature fluctuation (0.561), and beel siltation (0.503). The second PCA was anthropogenic activity, including the use of harmful fishing gear (0.702), application of urea to harvest fish (0.673), drying beels annually (0.531), and overfishing (0.513). Finally, the third PCA was loaded with the fishermen age (0.719), education (À0.767), and fishing experience (0.695) of the fishers. Deepening of beels could enhance dry season water availability and shelter the fish. Imposing fisheries regulations to reduce human activities is inevitable to sustain haor fisheries.

No abstract

Increased temperature, decreased water level and reduced culture period of the ponds with lack of guidelines in selecting appropriate stocking size, density and combination of species are major constraints for safe production of fattening based carps in drought prone barind area of Bangladesh. In order to address these problems, an experiment was conducted during July-December, 2018 to determine the suitable species combination for fattening ponds of overwintered carps in Tanore upazila (sub district) of Rajshahi district, Bangladesh. Three different combinations of surface (G. catla and H. molitrix), column (L. rohita) and bottom (C. cirrhosus and C. carpio var. specularis) feeding carp species were tested under 3 treatments (T1, T2 and T3), each with 3 replications: T1 (Surface-30%, column-40%, and bottom-30%), T2 (Surface-40%, column-30%, and bottom-30%) and T3 (Surface-35%, column-35%, and bottom-30%). Application of good aquaculture practices in the studied ponds was found to improve the environmental conditions of pond. Significantly (P< 0.05) highest fish yield was obtained from treatment T2 which was 21.47% and 11.89% higher than T1 and T3, respectively.  Significantly (P<0.05) highest cost benefit ratio was recorded with treatment T2 (0.42±0.02) followed by T3 (0.31±0.01) and T1 (0.21±0.01), respectively. Inclusion of appropriate number of fishes at different water layers of pond favoured the yield and economics of carp fattening. The study also suggests focusing on optimal stocking density together with the formulation of low cost feed for carp fattening in ponds under barind area of Bangladesh.

The present investigation was conducted in the Agronomy field laboratory of Bangladesh Agricultural University, Mymensingh, Bangladesh during May 1999 to August 1999 to reveal the food and feeding habits of Amblypharyngodon mola in the rice field ecosystem. Percentage of frequency of occurrence and percentage in number methods were used for the qualitative and quantitative estimation of plankton population. Results showed that, during the present study, the water quality parameters were within the suitable range for optimal fish growth and plankton population was abundant in the water of the rice plots. Gut content analysis of A. mola revealed a sum of 32 genera of phytoplankton belonging to Chlorophyceae (17), Euglenophyceae (2), Cyanophyceae (7) and Bacillariophyceae (6) and 8 genera of zooplankton under Rotifera (3), Cladocera (2) and Copepoda (3). In general, Navicula, Fragilaria, Chlorella, Chrysococcus, Closterium, Oscillatoria and Gomphosphaeria were found abundant both in the water of the rice plots and in the gut contents of A. mola indicating that, these genera are preferred food of this fish in the rice field ecosystem. Gut content analysis also exposed that, phytoplankton was the major food item constituting 94.38% of the gut contents’ composition of A. mola whereas zooplankton comprised only 5.62%. The results of this study conclude that, the A. mola is planktivorous in nature, feeding mostly on phytoplankton and could be a suitable species for integrated rice-fish farming.DOI: http://dx.doi.org/10.3126/on.v11i1.8245 Our Nature Vol.11(1) 2013: 61-75

This study describes the diets and feeding habits of Cyprinus carpio in integrated rice-fish farming system in the Agronomy Field Laboratory of Bangladesh Agricultural University, Mymensingh, Central Bangladesh during May 1999 to August 1999. Percentage of frequency of occurrence and percentage in number methods were applied for the qualitative and quantitative estimation of plankton. The water quality parameters recorded during the study were within the suitable range for optimal fish growth and plankton populations were also abundant in the water of the rice plots. The phytoplankton population recorded from the gut contents of C. carpio was under 4 groups (viz., Chlorophyceae, Euglenophyceae, Cyanophyceae, Bacillariophyceae) and the zooplankton under 3 groups (viz., Rotifera, Cladocera, Copepoda). Bacillariophyceae and Chlorophyceae were the dominant phytoplankton group while Rotifera was the dominant zooplankton group in the gut contents of C. carpio. This study also revealed that, gut contents of C. carpio was composed of 48.47% phytoplankton and 51.53% zooplankton indicating omnivorous nature of the fish. The availability of plankton population in the rice plots and the food and feeding habits of C. carpio suggest that, this fish could be a vital candidate for integrated rice-fish aquaculture.