Locally caught fish and invertebrates should probably never make it into your aquarium. They may look nice, are usually free, and require minimal effort to attain. Despite this, they can still be bad news for your reef tank. Locally caught animals can carry with them all sorts of parasites, bacteria, and diseases that may wreak havoc on the non-native fish you keep. For example, some of the parasites that fishes from the Gulf of Mexico and surrounding waters carry are microscopic gill parasites. They live on gill tissue and can become too great a burden for the fish to overcome, inevitably leading to its death. These parasites multiple rapidly and are found on just about every fish taken from the gulf. And unfortunately, these parasites won’t go away with a two week quarantine period, though harsh chemical treatments may kill them.