As I remember E.coli are not present in fish feces. Coliform bacteria as a group are present in feces of warm blooded animals and in soil. Fecal coliform bacteria of which includes Escherichia coli are present in feces from warm blooded animals and not fish or other cold blooded animals. I am not sure what type of bacteria are associated with their manure.

Water from the deepest layers of "dead zone" (hypolimnion or non mixing layer) will contain fertility for your plants however it may have odors associated with it. This water, if it contains sludge, will also be additonally fertile but it may pose problems in distributing it as sprays due to clogging of orfices or nozzles.

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