This study was carried out to investigate the genetic factors responsible for the differential growth in the artificial hybrid of C. gariepinus and H.bidorsalis. Five hybrids obtained from the crossing of female C. gariepinus and male H.bidorsalis were used for the experiment. The live fish was injected intraperitoneally with 0.02% colchicine (1ml/100mg body weight) and left for four hours. Fish sacrificing was done by pitting. The anterior head kidney was used for karyotyping according to the air-drying method. The weights of the stunted growing fish are: 0.2Kg, 0.4Kg and 0.5 Kg, while the fast-growing weighed 0.8Khg and 1.5Kg. C. gariepinus has a standard karyotype of 2n = 56, while H. bidorsalis has 2n = 52. The hybrids showed differential growth rate. The hybrids were sterile; no gonads were observed within the first year. Karyological observation revealed variation in the hybrid’s karyotype. Chromosome clumping was observed in hybrids that showed stunted growth. Further genetic studies should be carried out that will elucidate the genetic mechanism responsible for the differential growth of the hybrid.