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The fish is scratching against tank decorations, rocks or sides of the tank.
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There are visible spots, lesions, lumps, or white patches on the fish's body or fins.
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The fish's tail or fins appear frayed at the edges or are breaking off, disappeared.
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Red streaks near scales.
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The fish gasps at the surface of the water.
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Gills that are puffy or swollen and the gill tissue is bright red or even a grayish color.
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Clamped fins
Fish suddenly becomes really fat.
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The fish refuses its usual food for more than 2 days.
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The fish floats, sinks, whirls, or swims sideways.
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A normally active fish is still.
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A normally still fish is very active.
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Other fish alerting you of something going wrong by flashing or swimming frantically around tank .