Preclusion of saltwater fish illnesses.
1.    Do not overcrowd the fish tank. Crowding is the primary source of stress that can eventually lead to parasitic incursion.
2.    Confine newly acquired fish in a separate container for no less than two weeks.
3.    Use a good quality filter and regularly clean it since a lot of parasites hate moving water conditions.

Symptoms of saltwater fish illnesses.

1.    Loss of appetite- indication of intestinal disease
2.    Gasping for air- sign of gill rot or ammonia poisoning
3.    General paling- indication of lack of oxygen or tuberculosis
4.    Rocking of body and fin clamping- sign of general malaise or internal disease
5.    Resting at the bottom- indication of inflammation of the air bladder or tuberculosis
6.    Weight loss- sign of internal disease
7.    Red discoloration- indication of water in the abdomen or acidity damage
8.    Rubbing against object- sign of external parasites or acid toxicity
9.    Bulging eyes- indication of water in the abdomen or tuberculosis
10.    Bloating- sign of tumors or overfeeding
11.    Spinal and other deformations- indication of inherited abnormality
12.    Protruding gills- sign of thyroid tumor or gill parasites
13.    Skin ulcers- indication of bacteria
14.    Fin degeneration- sign of fungal disease
15.    White dots on the skin- indication of ichthy-opthiruis

Poisoning under saltwater fish illnesses.
Here are some products and/or chemicals that can cause poison in your fishes.
1.    Plastic- Your aquarium accessories such as plants or stones are usually made from plastic. Particularly dangerous on the fishes in the fish tank are the objects made of polypropylene that is slowly dissolves in water. One way to prevent this is to buy accessories that are solely made for aquariums.
2.    Poison from home stuff and owners’ habit- Even a cigarette smoke can cause poison to your aquarium. Home insecticides can cause poison as well. To prevent this kind of poisoning, make a conscious effort to cover your aquarium if you’re using home cleaning agents. If you’re going to smoke, make sure that you’re far from your fish tank.
3.    Spoiled food- Before feeding your fishes, check the quality of their food first. It doesn’t matter if it’s live, frozen or dry. The moment you realize it’s already spoiled or has molded throw already. If humans can’t eat rotten foods then why should we expect the fish to do so?
Proper caring for your fishes can go a long way. But of course, there’s always a possibility that your fish will get sick even if you do your assignment right. So another tip for you is to have an emergency medicine kit for your fishes. Ask for basic medicines from your vet and stock some at home. That way if there’s an unexpected illness you are prepared to cure it.