Assessment of the Hydrological Conditions of Carps Spawning Grounds in the Sylhet Haor Basins, and the Halda River System, Bangladesh

The Halda River and Haor basins are considered unique breeding habitats for carps in Bangladesh. The purpose of the study was to evaluate the natural spawning environment of carp species, with an emphasis on the hydrological conditions of the Halda River, the Surma River, and Tanguar Haor. This study, which covers the years 2021 and 2022, considered two spawning seasons. The results revealed that temperature, total dissolved solids (TDS), salinity, turbidity, conductivity, and pH were significantly different in the Halda River to the Surma River and Tanguar Haor. However, sudden rainfall and upstream runoff in 2021 were deemed as major factors causing an increment in TDS and electrical conductivity. The water pollution index was excellent in the Surma River and Tanguar Haor, and good in the Halda River. The study reported moderately reduced IMC fry production in 2021 because of inconsistent turbidity, high conductivity, and increased salinity which interrupted the ideal spawning habitat. However, in 2022, the spawning environment was favorable in the Halda River, while the Surma River and Tanguar Haor were considered to be comparatively favorable in both years. Differences were also found in the climatic and meteorological conditions, which revealed uneven rainfall, higher temperatures, decreasing water discharge, and low water levels. The meteorological data also revealed that the overall rainfall showed a decreasing trend for all sites in the last 20 years causing an interrupted water discharge. It was discovered that the amount of carp spawn obtained in the Halda River was greater than that obtained in the Surma River and Tanguar Haor. In terms of hydrological conditions and spawning performance, the Surma River and Tanguar Haor were reported to have significant differences, which may be due to their geographical location.