One of the primary goals in the area of ontogenetic research is to gain insight into the mechanisms underlying differential gene expression, as well as providing a more precise understanding of the evolution of the regulatory specificity of gene loci during embryogenesis. The research presented here relates the divergence in the regulation and expression of alcohol and supernatant malate dehydrogenase isozymes in both intraspecific and interspecific fishes in the teleost genus Barbus. Results from this investigation support the hypothesis that parental sensor genes can differ in their response to maternally controlled regulatory signals; suggestive of species specific effector/ activator RNA molecule concentrations and sensor/ receptor gene induction thresholds.