Far from barren, biologists say fishless lakes are hubs of biodiversity. Lacking piscine predators, they are home to a greater abundance and variety of invertebrates than lakes with fish, and provide breeding grounds for frogs, salamanders and waterfowl. But as fish are moved around — legally by fisheries agencies, illegally by anglers and bait growers — fishless lakes are becoming increasingly rare.Rugged and sparsely populated, the Maine woods have some of the last fishless lakes in the Northeast. Some, like this one, are kettle lakes without inlets or outlets, excavated in the eastern Maine lowlands by melting blocks of glacial ice. Others are clear tarns in high mountains, with outlets too steep for fish to ascend. Still others are simply too acidic for fish. All probably have been fishless since the glaciers receded.