✔️ If fish are dying in the aquarium for unknown reasons:
- Transfer all fish to another tank.
- Investigate what is happening.
Mass mortalities can vary:
⚠️ Different species are dying simultaneously. Different genera and families have distinct lifestyles, physiology, and immune responses. If multiple species die at once, the cause is more likely water chemistry rather than a pathogen.
⚠️ One species dies quickly and massively. This is also often related to water chemistry — the most sensitive species reacts first.
☣️ One species dies periodically, over time. In this case, infections or parasites are more likely, especially if this species has lower resistance (e.g., ciliates, bacteria).
✔️ If several individuals die in the same tank (mass mortality):
- Perform necropsies on several fish for comparison, to rule out individual pathologies.
✔️ A fish’s appetite is not an indicator of health
- Fish have very strong instincts. Even if a fish eats, it does not mean it is healthy.
The intestine may be non-functional (smooth, transparent, like a water-filled bag).
Such a fish eats but dies of starvation: the stomach and intestine contain no food fragments.
It is possible the fish vomits after feeding — but this often goes unnoticed.
Do not rely on appetite as a criterion of health.
✔️ If transferring fish from “dirty” water to clean water:
- Treat them for bacterial infections. Otherwise, the disease is likely to manifest later.
✔️ If the fish has been exposed to Cryptocarion irritans:
- Take regular scrapes and washes from the gills (at least once a month).
The gill form is invisible on the body… until it is too late.
✔️ If a fish dies during non-traumatic handling (bathing, transfer):
- Necropsy may reveal irreversible changes that could have caused death on their own.
Stress only triggered the death, which would have occurred soon anyway.
So don’t blame yourself immediately — perform a necropsy and then draw conclusions.
Most likely, the fish was already “doomed.”
✔️ If fungal hyphae (Saprolegnia) appear on the body :
- More often, the oomycete attaches to necrotic areas of skin or gills.
If the hyphae look like white fluff, it is most likely a saprophyte — not the cause, but a consequence, an indicator.
In “aggressive” oomycetes, the hyphae spread along the skin. The coating is denser, resembling wet cotton, and individual filaments are not visible.
✔️ If fungal hyphae are present on the fish:
- Treat bacterial infection at the same time.
Bacteria, ciliates, and flagellates always thrive in these fungal “thickets.”
Do not confuse bacteria with fungi — the size difference is enormous.
Strictly speaking, any poisoning by chemical agents is a form of chemical trauma.
