The Red Swordtail Xiphophorus hellerii, a globally popular ornamental fish, gains an increasing interest in Bangladesh due to its attractive color and its recent high commercial value. However, available information on habituation, feed acceptance, and effects of feeding on growth and body composition are scanty in Bangladesh. This experiment aimed at assessing feeding effects on the growth performance, adaptive habituation efficiencies, and whole-body carcass composition of X. hellerii in laboratory conditions. Fish fries (n=20) were fed with three different diets explicitly T₁-formulated diet, T₂-mega feed, and T₃-fast red feed, for 100 days in 9 uniform individual glass aquaria (capacity:105-litre, size:24×12×12 inches³). The water quality parameters did not significantly vary (P>0.05) among the treatments and were within the suitable limits for fish culture. In the end, significantly higher (P<0.05) final weight (2.05±0.100g), weight gain (2.00±0.107g), percent weight gain (4013.33±2140%), average daily weight gain (0.02±0.001 g/day), and survival rate (86.67±3%) were recorded in fish fed T₃ diet, compared to T₁ and T₂ diets. Significantly better nutrient utilization, viz. protein efficiency ratio (0.12±0.005) and lowest feed conversion ratio (1.21±0.020) were also recorded in fish fed T₃ diet. Analysis of X. hellerii whole-body carcass composition reveals that significantly higher (P<0.05) lipid (4.24±0.08%) and protein (15.078±0.55%) contents were recorded in fish fed T₁ diet compared to those fed T₃ and T₂ diets. Despite the lower growth performance, the carcass composition of fishes was higher in T_{1 than that} in T₂ and T₃. The higher lipid and protein content in fishes of the T₁ group reflected that the fishes fed with formulated feed well habituated over T₃ fed on fast red feed and T₂ fed on mega feed.