When one or more of the fish in your saltwater aquarium first start acting or looking "weird" is the time to start doing the research to determine what the problem is. Most marine fish diseases or afflictions, if detected, diagnosed and treated in their early stages can be corrected and cured.
To help with the diagnosis, check this list of potential symptoms. It can help you focus on a diagnosis and start early treatment. Utilizing a quarantine tank for treatment is usually the best course of action. If a number of your tank's occupants are showing the same symptoms, the entire tank should be treated.
Keep in mind that many of the treatments for fish diseases will weaken your tank's biological filter, so steps should be taken to minimize their effect on the "good bacteria" in your system.
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It has been said that when something goes wrong with a marine fish, the first thing to go is their appetite. Lack of appetite in marine fish is normally the first symptom of a more serious problem. When a fish is first introduced to a new aquarium system it is not unusual for a fish not to eat for a day or two because of their new environment and/or shipping stress, but they should start eating after that. Use tips on getting new fish to eat In your marine aquarium to help your picky eaters start eating.
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White Dots on a Fish's Skin or Fins
This is a sign of marine parasites which are known as Cryptocaryon, marine white spot disease, Ichthyophthirius multifilis (Ich), Oodinium, marine velvet, coral reef fish disease, Brooklynellosis, Brooklynella or anemonefish disease which can be difficult to identify. Since the treatment for these diseases is different, it is important to make a correct identification of the parasite before selecting a treatment.
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Popeye (an eye which is enlarged and protruding from its socket) is the result of an infection in the eye itself. It is normally caused by a scratch, abrasion or another injury to the eye which has become infected with bacteria which is in the surrounding water.
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Cloudy eyes may be a sign of a bacterial infection due to an injury on another part of the fish. The bacteria enters the body of the fish and then can migrate to the eyes, causing the cloudy appearance.
Introduction of the bacteria into the aquarium system can be poor environmental conditions. If conditions are poor enough, the bacteria can bloom and overrun even the healthiest of fish. White cloudy water with the presence of sores on the fish can be signs of this problem.Continue to 5 of 11 below.
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Rapid gilling (breathing rapidly) is a sign that the fish is not getting enough oxygen into its system. This can be caused by excitement, exercise or by the fish's gills being clogged by mucus, which inhibits the gills from being able to perform gas exchange (suffocation). If the fish is just swimming along normally, or at rest and it is gilling rapidly, it is a sign that the gills are clogged with mucus.
Quite often this is caused by parasites which are lodged in the gills and irritating them to the point that the fish's immune system will produce more mucus to protect them. Treat the fish for the appropriate parasite as soon as possible.
The other frequent cause of rapid gilling is an over-abundance of ammonia in the packing (shipping) water or aquarium water. While fish and invertebrates can tolerate a certain (low) level of ammonia (a toxin), higher levels can "burn" (irritate) the gills causing them to produce more mucus as a defense, which inhibits their ability to take in oxygen.
High levels of ammonia can also cause other problems with saltwater fish such as ragged, frayed or burnt fins and/or bacterial infections.
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Red fins on a fish usually indicate an internal bacterial infection caused by ammonia burns which allow the bacteria to enter the body and spread.Continue to 9 of 11 below.
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Bloating or Abdominal Swelling
Abdominal swelling or bloating is usually a sign of a bladder infection, often a common problem with wrasses that burrow in the substrate. Rarely, swelling or bloating can be caused by the "bends" (lack of decompression) which is the result of bringing a fish up from deeper waters after capture in the wild.
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Scratching on Rocks
When a fish is seen scratching or rubbing on rocks or other objects (even the substrate), it is a sign that the fish's skin is irritated and the fish is trying to remove the irritating material. The material is normally cysts from either Cryptocaryon (marine white spot disease, ich) or amyloodiniosis (Oodinium, marine velvet, or coral reef fish disease).