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

Allometry, condition index and sex ratio in freshwater mussel Lamellidens corrianus (Lea, 1834) were studied from the freshwater lake at Rajshahi, Northwest Bangladesh during the summer 2013. The collected mussel specimens ranged from 3.69 cm to 9.98 cm in length, and 4.82 g to 80.67 g in weight. The study was focused on the relationships between length-height and length-weights (length-total weight, length-tissue wet weight, length-shell wet weight, length-tissue dry weight and length-shell dry weight), which were found not to be significantly different between male and female (P<0.05). The calculated regression equation of length-height relationship for the entire study period was H= 0.5215L-0.1482 for combined sex. The equations of length-total weight, length-tissue wet weight, length-shell weight, length-tissue dry weight and length-shell dry weight relationships of mussel were W= 0.1756L2.6775, W= 0.0261L2.8919, W= 0.0261L2.5524, W= 0.0065L2.8946 and W= 0.095L2.5109, respectively for combined sex. The relationships between length and height were linear, while that between length-weights follow the non-linear pattern. The overall male to female sex ratio was 1: 0.92 and did not differ significantly from the expected 1: 1 ratio (x2-test, P<0.05). The condition index for male, female and combined sex was 13.54, 13.97 and 13.74, respectively. The results of this study will provide baseline information for fisheries researchers and for the further assessment and management of mussels in the freshwater ecosystems of Bangladesh.

Summary The present study describes the length–weight (LWR) of three fish species, Chela cachius (Hamilton, 1822), Coilia ramcarati (Hamilton, 1822) and Sardinella gibbosa (Bleeker, 1849) captured in the Bay of Bengal, Bangladesh, from December 2014 to November 2015. Fishes were captured with either gill nets (mesh size 2.0–5.0 cm) or set bag nets (mesh size 2.0–4.0 cm). The b values in the study varied from 2.88 (C. ramcarati) to 3.00 (S. gibbosa), with a mean a value of 2.94 at p < .001 for all three species. In addition, the study provides initial information on LWRs for C. cachius and C. ramcarati and maximum length records for C. cachius and S. gibbosa.

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.