River clams in fish tanks can cause the following four major hazards:1. Water quality problems: river clams release waste and feces, leading to deterioration of water quality, which may lead to ammonia poisoning and aquatic diseases.2. Ecological damage: river clams are not a local species, and they may escape and become an invasive species, destroying the balance of the local ecosystem and threatening other aquatic organisms.3. Disease spreading: river clams may carry diseases and parasites, which may cause fish infections and spread diseases when put in fish tanks.4. Moral problems: catching and stocking river clams violates the principle of nature conservation, and causes unnecessary damages to wildlife. May cause fish infections and spread diseases.4. Ethical issues: catching and stocking river clams goes against the principle of nature conservation and causes unnecessary damage to wildlife.