Sticks, bottles and stones were allegedly hurled by the Lankan navalmen at the fishermen and their boats also suffered damage in the attack, officials said.
They also snapped the fishing nets, and seized global positioning and wireless equipment.
The injured fishermen have been admitted to a hospital at Ramanathpuram.
Katchatheevu is an islet ceded to Sri Lanka by India under a 1974 agreement between the two countries.
