This manuscript considers general coupled dynamic equations on time scales with multiple and time-varying delays. The considered equations describe several continuous and discrete models as special cases. Using the coincidence degree theory approach, we investigate the existence of periodic solutions. The particular case describes the mathematical model of interacting phytoplankton when both species produce a chemical that is toxin to each other. The presented results extend and complement the existing results. Finally, some examples are presented to illustrate the analytical results.
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