Interannual variation in yield per species from a freshwater reservoir in Bangladesh was analysed by using long‐term landing data. Each species was categorized according to characteristics in interannual yield variation. The characteristics were defined with respect to size of the interannual variation in terms of absolute and relative variation around the mean yield and long‐term trends in catch levels. Annual variation was directly (t18 = 7.84; P < 0.01) related to the yield and can serve as a good indication of the status of the fishery when catches are low. The target fish, Indian major carps (IMC) Labeo rohita, Labeo calbasu, Catla catla and Cirrhinus mrigala, showed large variation in annual yield. This might have occurred because of variation in annual recruitment. Illegal use of gears is mostly related to variation in year class strength, and is assumed to be the most important source of change of stock variation. An increase in catch rate was recorded for Corica soborna. Such a stable combination may only be possible for a certain period without a long‐term trend. Trends in the yield rate of the major fish category for three decades reveal a sharp decline in the catch of IMC. In contrast, small clupeid‐like C. soborna have the highest yield rate. Fishing gears can play a crucial role in this fishery. Fisheries managers must always be alert when issuing fishing licenses and on the control on gears. The conclusion is that the IMC fishery of Kaptai Reservoir is an overexploited fish stock. In this fishery, the same gears are usually employed indiscriminately for different species and size classes. To stabilize the fishery, the existing policy needs to be strengthened and more effectively implemented. Also, some fishing gears and traps need to be restricted. An effective stock protection policy is suggested. Further study on catch size of individual species is essential prior to the development and implementation of any management scheme.

This study was carried out in four selected stations (Mohonpur, Kaligonj, Charludua and Daulatkhan) in the Meghna river system, Bangladesh between the latitude 22°35.494Ñ N - 23°23.987 N and longitude 90°35.793 E - 90°49.061Ñ E. Average net primary production (NPP) and gross primary production (GPP) (gC·m3 ·h) in the euphotic zone of the Meghna river were 0.089 ± 0.021 and 0.161 ± 0.025 respectively. The rate of conversion of GPP into NPP ranged between 48.17 and 62.63% with an average of 54.72%. The mean ratio of NPP to GPP (NPP:GPP), NPP:Respiration and average percent respiration rate to GPP were 0.549 ± 0.060, 1.251 ± 0.320 and 45.04 ± 6.02% respectively. The mean photosynthetic production for the day (gC·m3 ·day) and year (gC·m3 ·yr) were 1.930 and 704.45 respectively. Annual computed fish yield in relation to gross carbon synthesis was 7.0 kg fish·m3 ·year. The actual production of fish from the Meghna river is accounted about 0.21% of the estimated production. The gross energy production (Kcal energy·m3 ·day) by the producers was estimated about 18.0. The NPP of phytoplankton established a high significant negative correlation (r = -0.975; p < 0.01) with water temperature and low, but a definite negative correlation existed (r = -0.767) between GPP and water temperature.

A comprehensive analysis of the efficiency of different fishing gear in capturing Cyprinidae (major carp) species in Kaptai Reservoir, Bangladesh, was conducted. The catch per unit effort (CPUE) data were collected during a 1-year survey, covering a total of 493 independent fishing units spread across the four major fishing grounds of the reservoir. The study examines the CPUE and catch composition between months and study sites, and the effects of reservoir water level fluctuations, gear diversity and fish distribution patterns on the fish catches. The mean CPUE for all gear ranged between 2.91 and 30.86 kg unit −1 day −1 . Analysis of variance showed significant differences among the fishing gear types. The CPUE differed significantly between months for lift nets, large-meshed (LM) gill nets, cluster hooks and hand lines. None of the fishing gear exhibited significant differences between sites except for cluster hooks. The CPUE of small-meshed (SM) seine nets was significantly higher than that of other gear. The reasons for such differences in the fish catches were identified as the choice of fishing places, the net sizes, the number of hooks, lures and baits, water turbidity, wind, waves and rainfall. The CPUE indices for lift nets showed significant variation between months for the Cyprinidae species. A significant variation in catch at the different sites was found for all nets, except SM seine nets. The contribution of the Cyprinidae species showed significant differences between sites only for hand lines. The coefficient of variation of CPUE for fishing nets did not vary much more than 55% (lift net), whereas the highest variation of 49% was recorded for hand lines among the hooks and line. Higher reservoir water levels were followed by reduced CPUEs for the Cyprinidae species and vice versa, whereas the highest water levels corresponded to the higher CPUE for the Clupeidae species.

This paper examines the various challenges facing the development of fisheries resources in Kaptai reservoir, Bangladesh. The reservoir has undergone major changes in its catch composition since impoundment. Production records show a declining trend in the productivity of high-value fish. A host of managerial, socioeconomic and environmental factors are responsible for the underutilization of the reservoir's potential to provide high-value freshwater fish. These include deterioration of the natural breeding ground, environmental damage, poor implementation of regulations, inefficient fish farming technology and poor management practices. These constraints are discussed and possibilities for future improvements are suggested.

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