How can a fish survive horrible water quality?


This is something I'm wondering if there is a detailed answer to, because I'm fascinated and/or horrified by these things.

So, how can a fish survive in terrible conditions that should be quickly killing it? Example - the pleco I recently saved from a half filled 10 gallon with no running filter, that had been like that for at least a month. How can a foot long pleco survive in five gallons of filthy, stagnant water that is essentially sewage? Why would it show no labored breathing, ammonia burns, loss of appetite, lethargy, etc? The keyword here is 'surviving', obviously these sad critters are not thriving in any way.
Best Answer - View jkkgron2's answer


I think that over the years that these fish have been bred in captivity so much that they were starting to adapt to the less than perfect water parameters that humans were keeping them in. Plecos are especially hardy and IME have survived things most fish wouldn’t (seriously, mine jumped out of the tank yesterday.). Also it’s possible he did sustain internal damage that’s not affecting his appearance or behavior.


There's really no explaining why a particular fish survives sewer like water parameters in neglected tanks.
It's safe to say that the majority of fish residing in toilet tanks eventually succumb to disease or ammonia poisoning.


Let me ask you this—so I have an acquaintance who has not great water conditions for his guppies. They aren’t what you described, yet they aren’t great. If I were to put them in my tank with my weekly water changes, might they not die? And if I put mine in his, wouldn’t they die?


We also need to remember a lot of fish are not fragile little niche species, lots are very hardy and will adapt to whatever situation we can throw at them.

Evolution and natural selection are powerful tools when given millions of years.


A foot long Pleco in a 5 gallon would be very interesting.


Is the tank just covered in algae? Was he the only fish? I’m wondering if maybe the algae was taking up enough ammonia to make it survivable, and he would’ve adapted to high levels of such things as it slowly increased. As stated before, giving him goof clean water would probably shock him.


The water got that way over a long period of time. The fish acclimated to it as it gradually got worse. Pulling him out of there and dropping him in fresh clean water may be bad for him. I say "may be bad" because I don't know for sure.

To be safe while getting him used to clean water it would take lots of very small water changes and very gradually changing out more each time over a long period of time to acclimate him to fresh clean water.


Amazing creatures! I’m old af. Thinking back to some of the 10 gal setups we had as kids back before the internet, nooo google to be seen for years thereafter lol Somehow we had what we thought were “successful” tanks. I feel horrible now :banghead:


I also.wonder! I do everything right, and have had a few issues. My aunty had a goldfish in a 5 gallon tank it lived 6 years.....still not great as they can live 25 years but it still survived that long!

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