The analysis of the expression of isozymes during the development of interspecific hybrids has proven to be an excellent means of drawing inferences about the action of regulatory gene loci. The research presented here relates the divergence in the regulation and expression of lactate, isocitrate in both intraspecific and interspecific fishes in the teleost genus Barbus. Results from this investigation support the hypothesis that parental sensor genes differ in their response to maternally controlled regulatory signals; indicative of species specific effector/activator RNA molecule concentrations and sensor/receptor gene induction thresholds.