It is understandable in the case of fish. As every ritual and belief must have some reasons behind. To release fish to river is not only to make merit but it also turns the fish back to water source to be a breeder. By doing so, river will be fertile with water animals and keep balance the eco system. However, the old belief says that you shouldn’t eat the kind of fish that you set free (that’s why many people choose the eel or some kind of fish that are not used as food).