The present investigation was concerned with the fish biodiversity of old Brahmaputra River under Mymensingh district of Bangladesh. Objectives of the study were to determine biodiversity and abundance of fish, and to assess seasonal abundance and variation of fish in the river. A semistructured questionnaire was used to collect the pertinent information from 40 randomly selected fishermen from the study area. A total of 55 species of fish and shell fish were recorded from study sites. Among them, 8 species of carps, 4 species of snakeheads, 8 species of perches, 3 species of eels, 13 catfishes, 8 species of barbs, 2 species of minnows and clupeid species, 3 species of shrimp and other miscellaneous 4 species. It was found that 13 species were abundant, 19 were common, 14 species were less common, and 9 species were rare. The fishermen and other local elites reported that fish population in the old Brahmaputra River has been declining very fast over the last decades may be due to change in water current, depth of water, over fishing, temperature etc.

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The experiment was conducted to determine the effects of different amounts of organic fertilizers on growth and production of Tilapia (monosex GIFT tilapia) in monoculture system for a period of 120 days. The experiment was carried out in six earthen ponds, which were situated at the south-east corner of the Fisheries Faculty Building under the Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh. The experiment was designed with three treatments and each of them consisted of two replications. Fish population density was 120 fish per decimal for all the treatments. Ponds were treated with organic fertilizers (cow dung) at the rate of 2 kg, 4 kg and 6 kg per decimal were supplied fortnightly for treatment-I, treatment-II and treatment-III, respectively. The ranges of water temperature, transparency, dissolved oxygen, total alkalinity, free CO2, phosphate-phosphorus and nitrate-nitrogen found were 15.82 to 24.49 ºC, 17.00 to 32.00 cm, 7.00 to 10.30 mg L-1, pH 7.20 to 7.90, 140.00 to 192.00 mg L-1, 2.00 to 6.00 mg L-1, 1.40 to 1.95 mg L-1 and 3.30 to 3.73 mg L-1, respectively. All the physical and chemical parameters except temperature were within the productive range and more or less similar among all the ponds under three treatments. 18 genera of phytoplankton under five major groups and 9 genera of zooplankton under three major groups were identified in the experimental ponds. Average survival rate of fish under treatment-I, treatment-II, and treatment-III were 94.50%, 94.00% and 95.00%, respectively. The calculated net fish production under treatment-I was 3.554 ton ha-1 yr-1 and that under treatment-II was 3.648 ton ha-1 yr-1 and under treatment-III was 2.919 ton ha-1 yr-1. The net fish productions under treatment-II and treatment-III were 102.64% and 82.13% comparing with treatment on which was taken for 100%. According to cost-benefit analysis, the ratios of net profit under treatments I, II, and III were 1:0.81, 1:0.54, and 1:0.04. According to specific growth rate, treatment-II was the best and survival rate of treatment-III was the best, and according to cost-benefit analysis, treatment-I (ratio 1:0.81) was the best. So, organic fertilizer at the rate of 2 kg per decimal (treatment-I) was considered the best among three treatments in this experiment. Int. J. Agril. Res. Innov. & Tech. 8 (2): 24-31, December, 2018

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The study was conducted to observe the biodiversity of Shorupdah Beel, fish species, non-piscine animal species and the aquatic vegetation. This beel riches with its biodiversity and most of them are consume by the people of surrounding area. This water body not so deep compare with its biodiversity, highest 5-6 feet in rainy season. A total fifty two species belong to ninteen families under nine orders were identified non-piscine biodiversity of Shorupdah Beel comprises five species of prawns, four species of mollusks, three species of arthropods, two species of amphibians and two species of reptiles. Only fish and prawn are consumed by local people and the highest catch found just after rainy season that is during August and September. Ten species of aquatic vegetation found in this beel. Among these some are edible and some are not. Fishermen and local people said that biodiversity has been declining very fast over the last decades due to change of water depth, over fishing, temperature, use of chemicals in agriculture etc.