A coordinated patrol involving a CG ship and aircraft apprehended the boats and fishermen about 70 nautical miles off north east of Chennai, a Coast Guard (CG) release here said.
"The Sri Lankan fishing boats had 4200 kg of tuna fish illegally caught from the Indian exclusive economic zone," it said.
The fishermen along with the boats will be handed over to city police, the CG release said, adding Coast Guard has apprehended 31 Lankan boats and 159 crew this year so far.