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My active fish is suddenly lethargic and won't eat. Is it sick?

Updated On September 23rd, 2025

Pet's info: Fish | Saltwater Fish | Male

Hello, hal was an active fish but suddenly he was stagnant and didn't eat well. Is this normal? Thanks.

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2 Answers

Most Helpful Answer

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Answered By Todd Cecil

Veterinarian

Published on November 7th, 2018

Thanks for reaching out about Hal and including pictures. It is not normal for once active fish to become lethargic. Firstly, test the water quality for pH, ammonia, nitrate and nitrite, and correct any abnormalities. next, check the nutrition. All fish have a requirement for vitamin C, and this vitamin is not stable in pelleted foods for long (typically 3 months). Different fish pellet brands have different nutritional values, so varying brands could help. If your fish appears sick, seeking an appointment with a fish veterinarian is needed for a diagnosis and to determine a treatment. Good luck.

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    Answered By Dr. Massimo Orioles, DVM, Cert AVP, MRCVS

    Veterinarian

    Published on November 7th, 2018

    These are quite generic but concerning signs. The list of differentials is very long in this case, so I would recommend a logic and radical approach. Begin by submitting a water sample for quality testing. Most pet stores will do this for free or a nominal fee. Clinical examination should always include a water quality check, even if you have done so already. Water testing should be performed with a quality test kit, measuring NH4, NO2 and NO3. High ammonia levels, PH imbalances may be responsible for these signs. Oxygen concentration and quality of the filters should be determined as well. If water quality is good and there are no major imbalances, your fish should get examined to look for any sign of bacterial/fungal infection and eventually water should be treated. Hope this answer was helpful, but please do not hesitate to contact us again on the forum or by requesting a consultation if you have any more questions or to discuss it any further. Please find the time to give us a feedback about the consultation as that will be used to improve our service.

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