i study toxicology. a good deal, if not the majority of the chemicals put in an aquarium bioconcentrate, bioaccumulate, and biotransform. Basically, this means you put a chemical in your water, it undergoes changes to its structure through reactions with microbes/bacteria, which can make it more toxic. Your fish uptake not only the original chemical, but now the new one that may potentially be more toxic to humans now. Over months and through the years, the chemicals going into a tank and accumulated in the fish. It may not be harmful to them, but their tissues may be packed with metabolites of the chemicals. Lastly, many toxic chemicals bioconcentrate, meaning their toxicity goes up as it moves up the food chain. So, by treating your water, first the bacteria metabolize it, then the fish (now more toxic to the fish), and then if a human eats the aquarium fish you are receiving an exposure that could potentially be very high.
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not likely to be fatal but definitely has the scientific basis to be. depending on how old your fish are, how often and dosage of chemicals, water quality and filtration, your dose of toxic chemicals and metabolites could be low or extremely high.
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if you eat your own home raised aquarium fish, you are sick, bottom line.