Viable interspecific hybrid seabream were produced by artificially inseminating red seabream, Pagrus major (Temminck et Schlegel) eggs with black seabream, Acanthopagrus schlegeli (Bleeker) sperm. Cytogenetic traits of the hybrids, chromosome numbers and karyological analysis, cellular DNA contents by flow cytometry, and erythrocyte nucleus sizes, were intermediate between the parent species. The hybrid seabream karyotype consisted of each haploid set of parental species chromosomes. A histological analysis of gonads from juvenile hybrid seabream fish showed abnormal and retarded gonad development. The sterility of the hybrid seabream offers a significant advantage for their use in aquaculture, as potential escapes would not jeopardize natural stocks.