Selective breeding, hybridization, triploidy and tetraploidy by heterospecific insemination are genetic methods for generating male or female population capable of producing diploid (2n) or triploid (3n) gametes. The generated allotetraploids (4n) will thus serve as gamete providers for generating auto and allo-triploids, tetraploids and androgenetic clones. In the present study, we generated an allo-tetraploid population by crossing wild type black widow tetra (WT), Gymnocorymbus ternetzi (Boulenger) females with either wild type gray or recessive golden androgenetic Buenos Aires Tetra (BT), Hyphessobrycon anisitsi (Eigenmann), males followed by arresting the Ist mitotic division of hybrid embryos with thermal shock to study their early embryonic development and survival. The 22-min post fertilization hybrid embryos were subjected to heat shock at 41ï‚°C for 2 min or cold shock at 4ï‚°C for 2 min; maximum hatching success of tetraploids ranged between 2 - 5%. Survival of tetraploid tetras was lowered by embryonic mortality especially after gastrulation stages. Karyotyping and erythrocyte measurements confirmed successful induction of tetraploidy. The tetraploid red blood cell (RBC) nuclear volume increased 2.2 times than its diploid counterpart and the chromosome numbers doubled (94) in tetraploids. Causes for such high incidence of mortality at hatching and reasons for survival of interspecific allotetraploids are discussed.