Marine fish are prone to diseases in their native and aquarium environment. Several reasons lead to this sickness. It’s important to know about these reasons for proper care. This article will highlight some marine aquarium fish diseases, their causes, and a procedure to find the root disease in your marine fish.
Content Table
marine fish diseases
Marine Fish Diseases
Like every living being, marine fish also suffer from sickness. There are several reasons behind their sickness. Here are some common diseases categorized under their cause that marine fish usually get in the ocean.
| Parasitic Diseases | Bacterial Diseases | Viral Diseases | Fungal Diseases | Environmental Disorders |
| Marine White Spot Disease | Vibriosis | Viral Hemorrhagic Septicemia (VHS) | Egg Fungus | Heavy Metal Toxicity |
| Fish Lice (Argulosis) | Mycobacteriosis | Lymphocystis Disease | ||
| Flukes (Monogenean/Digenean) | Furunculosis | Infectious Hematopoietic Necrosis (IHN) | ||
| Nematode Infections |
Symptoms of a Sick Marine Fish
Every disease has its specific cause and effect. We have previously discussed some common diseases. Here are the symptoms of those diseases in marine aquarium fish.
| Symptoms | Causes |
| White Spots on Body | Parasitic infection due to Cryptocaryoniasis |
| Scratching Against Surfaces | Fish lice or fluke parasites |
| Lethargy | Viral infection |
| Bacterial attack | |
| Stress due to poor water quality | |
| Respiratory Distress | Parasitic gill infections |
| Hypoxia | |
| Harmful algae blooms | |
| Skin Ulcers or Lesions | Vibriosis bacterial infection |
| Furunculosis bacterial infection | |
| Fin Erosion or Rot | Columnaris |
| Bacterial fungal growth | |
| Abdominal Swelling | Internal infections |
| Viral diseases, e.g., Novel megalocytivirus and Infectious pancreatic necrosis | |
| Parasitic worms, e.g., Roundworms | |
| Erratic Swimming | Neurological damage from toxins |
| Infections | |
| Poor health | |
| Loss of Appetite | Stress |
| Illness | |
| Climate change | |
| Gasping at the Surface | Gill infection |
| Low oxygen level | |
| Discoloration | Stress |
| Infection | |
| Malnutrition | |
| Cotton-like Growths | Saprolegniasis |
| Bulging Eyes | VHS infection |
| Injury | |
| Poor water quality | |
| Reduced Activity | Malnutrition |
| Infection | |
| Environmental stress |
Marine Aquarium Fish Diseases in Home Tanks
Aquariums or home tanks are artificial environments to keep in-house fish. Unlike the ocean, marine fish are highly susceptible to numerous diseases because of aquarist negligence or the difficulty of mimicking their natural habitat. Here are some marine fish diseases with their causes and effects.
| Disease | Cause | Effect |
| Fungal Infections | Saprolegnia and other fungi | Cotton-like growths on skin, gills, or fins |
| Lethargy | ||
| Weakened immunity | ||
| White spot disease | Cryptocaryon irritans (protozoan parasite) | White spots on the body |
| Scratching | ||
| Respiratory distress | ||
| Lethargy | ||
| Brooklynella hostilis | Protozoan parasite | Mucus overproduction |
| Gill damage | ||
| Lethargy | ||
| Rapid breathing | ||
| Dropsy | Bacterial infections or organ failure | Abdominal swelling |
| Pinecone-like scales | ||
| Lethargy | ||
| Flukes | Monogenean | Gasping |
| Inflamed gills | ||
| Digenean flatworms | Excess mucus | |
| Tissue damage | ||
| Lymphocystis | Iridovirus infection | Cauliflower-like growths on skin or fins |
| Bacterial | Aeromonas | Ulcers |
| Vibrio | Fin rot | |
| Flavobacterium | Lethargy | |
| Systemic infections | ||
| Lateral line Erosion | Poor water quality | Pitting along the lateral line |
| Nutritional deficiency | Loss of tissue | |
| Metazoan parasites | Worms | Visible parasites |
| Inflamed skin | ||
| Crustaceans (e.g., nematodes, lice) | Anemia | |
| Weight loss | ||
| Swim bladder | Injury | Difficulty swimming |
| Infection | Floating upside down | |
| Improper diet | Sinking | |
| Velvet | Oodinium dinoflagellates | Gold dust-like coating |
| Lethargy | ||
| Respiratory distress | ||
| Fish Ich | Ichthyophthirius multifiliis | White cysts on skin, fins, or gills |
| Erratic swimming | ||
| scratching | ||
| Hemorrhagic Septicemia | Viral infection (e.g., VHSV) | Hemorrhages on skin, fins, or organs |
| Bulging eyes | ||
| Lethargy | ||
| Marine Ich | Cryptocaryon irritans | White spots |
| Rapid breathing | ||
| lethargy | ||
| Popeye (Exophthalmia) | Infection | Bulging eyes |
| Injury | Potential vision loss | |
| Poor water conditions | ||
| Fin Rot | Aeromonas | Fraying |
| Pseudomonas | Discolored fins | |
| Fungi | Tissue loss | |
| Ichthyobodo, Cryptobia | Protozoan parasites | Lethargy |
| Mucus production | ||
| Weight loss | ||
| Enteric Red Mouth | Yersinia ruckeri bacteria | Redness around mouth and gills |
| Systemic infection | ||
| Hole in the Head | Poor water quality | Erosive lesions on the head |
| Stress | Lethargy | |
| Nutritional deficiencies | ||
| Pseudomonas Infection | Pseudomonas bacteria | Ulcers |
| Fin rot | ||
| Systemic infections | ||
| Rapid mortality in severe cases |
Find the Most Close Symptoms Matches Your Marine Fish’s
Various diseases have different symptoms. Sometimes, it’s difficult to diagnose the exact disease or cause with a simple examination because some symptoms are common in multiple diseases. In such a situation, the best solution is to narrow down the symptoms to determine the exact cause.
Examination
The examination is the primary step to finding the exact reason behind your slow or diseased fish. Here are the simple steps.
Observe Your Fish
- Look at your fish for any visible symptoms, e.g., spots, holes in the head, wounds, fully or partially missing fin, discoloration, etc.
- Observe their behavior, e.g., swimming pattern, breathing normally, etc.
- Check their feeding behavior, i.e., whether they are eating or have appetite loss.
Observe Your Tank
Regularly check the water parameters, as fish are sensitive to water parameters. pH, water temperature, ammonia, hardness, salinity, nitrates, and nitrate levels are important water parameters. Moreover, keep an eye on population density or some filtration issues.
Symptom Table
Look at the following symptom table after a physical examination and water parameter check. Match the symptoms to find the exact problem.
| Symptoms | Diseases |
| White spots on the body or fins | Marine Ich (Cryptocaryon irritans)
Fish Ich |
| Golden or rust-colored coating | Velvet Disease (Oodinium or Amyloodinium) |
| Scratching against surfaces | Parasitic infections, i.e., Ich, Velvet, Flukes, etc. |
| Fraying or discolored fins | Fin Rot, i.e., Aeromonas, Pseudomonas, etc. |
| Bulging eyes | Popeye |
| Cotton-like growth | Fungal infections, e.g., Saprolegnia |
| Rapid breathing | Gill parasites
Velvet Poor water quality |
| Lethargy | General stress
Bacterial or viral infection |
| Loss of appetite | Internal parasites
Poor water quality |
| Ulcers or open wounds | Bacterial infections, e.g., Vibriosis |
| Abdominal swelling | Dropsy |
| Erratic swimming or difficulty swimming | Swim Bladder Disease
Neurological damage |
| Redness around the mouth or gills | Enteric Red Mouth, e.g., Yersinia ruckeri |
| Pitting or erosive lesions on the head | Hole in the Head |
| Visible parasites on the skin | Fish Lice
Flukes Metazoan parasites |
Narrow Down the Cause
If you are still vague about the exact reason, follow the following steps.
- Maintain the optimal water parameters to rule out environmental factors.
- Maintain the adequate population intensity and add some compatible tank mates.
After stabilization, recheck the fish’s behavior numerous times. Try to understand by making combinations. Consult an expert or vet, or go to a credible online aquarium shop or forums to determine the disease or cause.
marine aquarium fish diseases
Closing Remarks
Marine fish can become victims of several diseases in their native environment. A sick fish has several visible behavioral and physical changes, such as erratic swimming, loss of appetite, dull coloration, etc. As aquariums are not their natural habitat, marine fish are more prone to these diseases.
Closely examine the fish, check water parameters, and match the symptoms to the table to find the exact cause. If you are still not sure, recheck the water parameters and try to combine different causes to find the root cause.
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