The fishermen said that the navy personnel stripped some members, before beating them with sticks and stones.
The fishing equipment was damaged, and there remain unconfirmed reports that twenty boats were damaged in the attack.
See here and here.
Fishermen from Tamil Nadu have reported attacks by the Sri Lankan navy, who accuse the fishermen of straying into Sri Lankan waters.
Talks between the two countries to end the violence and damage to the livelihoods of the fishermen have proved futile.
Earlier this year, the now prime minister, Ranil Wickremesinghe was fiercely criticised by Indian officials for apparently justifying the Sri Lankan navy's use of force against the fishermen.
"If someone tries to break into my house, I can shoot. If he gets killed...Law allows me to do that," Mr Wickremesinghe told an India TV programme.
Related articles:
India criticises Sri Lanka’s ‘use of force’ against Tamil Nadu fishermen (24 Jun 2015)
Sri Lanka PM reiterates navy can shoot Indian fishermen in its waters (16 March 2015)
Indian parliament expresses outrage over Sri Lankan PM defending shooting of fishermen (09 March 2015)