Physico-Chemical Parameters, Length-Length and Length-Weight Relationships and Condition Factor of the Vulnerable Gudusia chapra in the Kaptai Lake, Rangamati, Bangladesh

Fish growth is directly influenced by water quality and the abundance of food in their environment. The aim of this study was focused to determine the length-length, length-weight and condition factor of Gudusia chapra inhabiting in the largest man-made lake in Bangladesh aligned with water quality parameters (temperature, pH, dissolved oxygen (DO) and total dissolved solids (TDS)) of the lake. A total of 600 specimens were collected from October 2018 to March 2019 using a cast net. Three different forms of length (Total length, TL; Standard length, SL; and Fork length, FL) sided with the body weights (BW) of the samples were measured to determine the length-length and length-weight relationship. Temperature, DO, pH, and TDS were recorded to be 24.8 - 25.7°C (25.27±0.38), 6.9- 7.8 (7.37±0.05), 6.1 -6.7 mg/l (6.4±0.3) and 60-110 ppm (79±2.0), respectively. The mean TL, SL, FL and BW were 8.588 ± 0.780 cm, 6.830 ± 0.644 cm, 7.390 ± 0.708 cm and 5.712 ±1.636 g, respectively. The month-wise values of correlation coefficient (r) of the relationships between TL vs SL, TL vs SL, and SL vs FL were determined as 0.96 to 0.98, 0.91 to 0.98 and 0.91 to 0.96.  The ‘r²’ values of the TL vs BW, SL vs BW and FL vs BW vacillated 0.91 - 0.94, 0.92 - 0.94 and 0.90 - 0.92, respectively. The values of the ‘r²’ reflected that every relationship had a high degree of positive correlation. Furthermore, the length-weight relationships of the fish had regression coefficients ranging from 2.50 to 2.93, suggesting a negative allometric growth trend. The condition factor (K) ranged from 0.97 to 1.25, suggesting that the lake organisms were in good health. The findings of this study might be used as basic biological information to manage a sustainable production of this vulnerable G. chapra.