REPRODUCTIVE BIOLOGY OF INDIAN MAJOR CARP (BLACK ROHU, Labeo calbasu) FROM THE KAPTAI LAKE OF BANGLADESH : A STUDY TO BROODSTOCK MANAGEMENT

Abstract

Life-history knowledge is significant for dynamic conservation, population growth, and broodstock management of fish populations, particularly for fish with high monetary worth. However, to date, very little is known about the life-history of commercially important carp fish species; therefore, this study aimed to investigate the reproductive biology of the Black Rohu, Labeo calbasu, in the Kaptai lake of Bangladesh from November 2020 to October 2021. Analyses of morphometric parameters revealed the exponent ‘b’ value of the standard length-weight relationship of L. calbasu was 2.9035 for both sexes; 2.4481 for males, and 3.0077 for females, indicating negative allometric growth (b < 3) for both sexes combined and for males, whereas isometric growth for females (b = 3). The average mean condition factor (K) and average mean relative condition factor (Kn) values were 1.453 ± 0.077 and 1.014 ± 0.055, respectively, indicating the fish's good health. The maximum mean HSI value was 1.19 ± 0.10 in July for males, and 1.25 ± 0.36 was found in February for females. The mean GSI value ranged from 0.05 ± 0.01 (December) to 2.14 ± 0.56 (June) in males and 0.23 ± 0.10 (December) to 19.5 ± 2.42 (June) in females. The oocyte diameter was found to be maximum in June (1152.9 ± 115.2 μm), and that was minimum in December (65.9 ± 49.9 μm). The oocyte diameter showed a positive relationship with GSI value, with the largest oocyte size and the greatest GSI value in June. Based on the gonado-somatic index, modified gonado-somatic index, and Dobriyal index, the length at first sexual maturity (Lm) was calculated as 40.0 cm TL for males and 41.5 cm TL for females. The fecundity was determined from randomly collected gravid female fish samples and varied from 446,264 to 1,063,644 eggs/individual with an average value of 828,198 eggs/individual. The GSI, oocyte diameter and gonadal maturity in males and females were synchronized in this species, indicating a single spawning period annually and its ranges from April to June. The study findings will be helpful in the management of L. calbasu and related species in the Kaptai lake, Bangladesh.