Navy spokesman Kosala Warnakulasuriya told Xinhua that the Indians were arrested at two separate locations.
Wednesday evening 19 were caught off the northern seas of Mannar while Thursday morning another 34 Indians were arrested off Delft islands, also in the north.
Warnakulasuriya said the boats used by the fishermen were seized and they would be handed over to police for investigation.
Earlier this week, 16 fishermen, arrested for fishing in Sri Lankan waters, were sent back to India.
Indian and Sri Lankan fishermen often stray into each other’s territory as both countries are divided by a small strip of sea.
Indian fishermen often accuse the Sri Lankan navy of attacking them when they stray into Sri Lankan waters, an allegation Colombo denies.