Saltwater fish are susceptible to some of the same disease you see in tropical aquariums. As always, determining the cause of the illness is the most important thing! Many diseases are caused by stress in the fish, whether from transport, water quality, or trouble acclimating to the tank.
Quarantine tanks are even more useful for saltwater aquarium hobbyists than they are for tropical aquarium hobbyists! Your saltwater fish can live in your quarantine tank for a few weeks before entering the main tank; this gives them time to acclimate and time for you to make sure the new fish are free of disease.
- Ammonia poisoning — symptoms include red or inflamed gills, and fish gasping at the surface for air. You can avoid ammonia poisoning by completing the nitrogen cycle before adding any fish to your tank.
- Dropsy — symptoms include bloating and raised scales. This is a symptom of a bacterial infection; more frequent partial water changes can help.
- Hole in the head — symptoms include small holes or indentations on the head or lateral line of the fish. Poor water quality and poor nutrition may be at fault here; try frequent water changes and vitamin enriched foods.
- Ich (also known as Ick) — symptoms include small white spots appearing on the fins or all over in advances cases. Fish may also rub against objects in the tank. This common fish disease can be treated with medication from your local pet store; ich is often a symptom of stress.
- Nitrite or nitrate poisoning — symptoms include lethargy and resting just below the surface. Check your water quality; you may see very high readings on nitrates and nitrites. A partial water change will make an immediate difference.
- Oxygen starvation — you will see your fish at the surface; they may be gulping for air. If the temperature is too high, your fish need more oxygen. Increase aeration in the tank and try to bring the temperature down by turning off the tank light and floating ice cubes in the water (put them in baggies first).
- Velvet — looks similar to ich, but the spots may be smaller and white or dusty grey. This disease can be treated with medication from your local pet store.
You may want to consider keeping “cleaner” species in your aquarium — fish and shrimp that can clean parasites and dead tissue out of the tank. Look at the skunk cleaner shrimp and the neon goby; many hobbyists have had great success with these cleaner species. Longfin bannerfish clean other fish when they are young.