SO now I have 10 fish in a 10 gallon tank, instead of 2. They are dying bc they require more resources and fresh water to live a healthy and happy life. The fish will grow to be smaller and weaker, with lower lifespans. The weaker fish will resort to worse food or cannibaism. As they grow and multiply the water will become more polluted until they all suffer constantly and die. Some fish will murder everyone if they anticipate the "puddle" won't support everyone.