Take your rod & bait, and take a boat out about 50-100 feet from shore, where it is still shallow, but where you can still visably see fish. Cast only about 3 or 4 meters tops. Fish will swarm to it, and you won't get bothered by mob spawns. I have caught at least 150+ fish this way (the chunky purple ones) that give 4 fish each. Didn't even have food buff, but did have rested buff, so you can fish on an empty stomach and still catch heaps of fish.