The Department of Fisheries has expressed concern at the release of freshwater animals as a way to make merit and urged people to think more carefully about the impact on local ecosystems.
Releasing freshwater animals into natural water sources such as rivers and canals is often considered a good deed among Buddhists, especially on special occasions like Songkran.
However, fisheries department's chief Bancha Sukkaew on Saturday warned that what are intended to be acts of kindness pose a danger to the natural balance, as the release of these "alien species" can have an unpredictable impact.
Giant catfish should be released only into large reservoirs or the Mekong River, while eels prefer to live in muddy water with slow currents, he advised. Russian catfish and tortoises are also among the species least suited for release into the wrong habitat, he said. "Alien species can cause huge damage to the ecological system which is costly to restore," he said.
Merit-makers wanting to release turtles must be sure they are water turtles and not tortoises (land turtles), which will drown and die. The main difference between them, he said, is that turtles have webbed feet which help them swim.
Those who want to release a large school of baby fish should make sure that they are healthy and disease-free. The release should be done at places with good water quality and in the morning or late afternoon, he added.