Chromosomal and karyotypic studies are required for genetic improvement of any organisms. This study was performed to identify individual chromosomes on morphological basis and to characterize a standard karyotype using the fish, Rohu (Labeo rohita, Hamilton, 1822). Colchicine (0.05%) treated (2, 2.5 and 3 h) tissues of two day-old larvae were used for slide preparations and selected plates were photomicrographed under high resolution research microscope. Slide preparations were done following hydrolysis (10% HCl), mordanting (2% iron alum) and staining with haematoxylin. Colchicine treatment for 2 h gave satisfactory results in respect of degree of contraction of the chromosomes. Chromosome number 2n = 50 was counted at metaphase stage. Measurements of the chromosomes were taken from the selected plates based on morphologically distinct condition. Standard haploid karyotype was formulated following the combined scatter diagram technique. Six individually identifiable and 19 not individually identifiable chromosomes consisted of the haploid complement. The six individually identifiable ones consisted of 2 m+3 sm+1st and not individually identifiable ones consisted of 16 m+3 sm chromosomes. This study report may provide complete report on chromosomal and karyotype knowledge in L. rohita and suggest the genetic purity of L. rohita may contributes to sustainable aquaculture production.

Experiments were conducted for a period of 90 days to estimate the effects of different feeding frequencies (one time per day: T1, two times per day: T2, three times per day:T3 and four times per day: T4) on growth performance of gulsha fish reared in laboratory facilities. Significantly higher condition factor was observed in T2 (1.61 ± 0.02) and lowest in T4 (1.40 ± 0.01). Significantly lowest SGR and ADG were recorded in T4 fish fed four times per day. No significant difference was obtained among different treatments for FCR and survival rate. The highest RNA : DNA ratio (0.93 ± 0.07) was observed in fish of T2 and the lowest ratio (0.57 ± 0.11) was observed in fish of T1. The results of the present study suggest that in laboratory rearing two meals per day could be supplied for better growth performances as per indication of condition factor and RNA:DNA ratio. Dhaka Univ. J. Biol. Sci. 27(1): 75-83, 2018 (January)