Why do my fish get sick?

[Daniel]

You often see something like, "my fish are dying because of a fungal infection". I suspect it is the other way around. That is, "your fish are dying, and that is why they have a fungal infection.

With the exception of a few diseases like ich which can spread rapidly when you see that most of the fish in an aquarium are sick, it is because of poor environmental conditions.

It is useful to ask why many times. Something like:

1. Why are my fish lethargic? Answer: My fish have a fungal infection.
2. Why do my fish have a fungal infection? Answer: My fish's immune systems were compromised and this led to a fungal infection that normally would have been warded off.
3. Why were my fish's immune systems compromised? Answer: Poor environmental conditions.
4. Why do I have poor environmental conditions? Answer: Now there is the real mystery, because when the parameters were measured they were "all perfect". Hmm...everything is perfect and yet the fish are sick?

I think it is all too easy sometimes to confuse the cause (environment) with the effect (sick fish).

[BNye]

@Daniel I agree, I also think that a lot of people jump immediately to what medications do I use to fix the problem. When in reality the problem is the parameters or another stress and the disease is the bi-product of that stress. As the medication may temporarily help the fish in the long term, an illness will most likely come back rather the same illness or another.

I also think that it is easy for some to jump to adding all the medications rather than identify and  utilize a medication specific to an illness. It is often us adding medications that we don't understand or that are not effective for our illness that deals more damage to the fish that the illness itself.  

[Ken Burke]

5 hours ago, Daniel said:

You often see something like, "my fish are dying because of a fungal infection". I suspect it is the other way around. That is, "your fish are dying, and that is why they have a fungal infection.

With the exception of a few diseases like ich which can spread rapidly when you see that most of the fish in an aquarium are sick, it is because of poor environmental conditions.

It is useful to ask why many times. Something like:

1. Why are my fish lethargic? Answer: My fish have a fungal infection.
2. Why do my fish have a fungal infection? Answer: My fish's immune systems were compromised and this led to a fungal infection that normally would have been warded off.
3. Why were my fish's immune systems compromised? Answer: Poor environmental conditions.
4. Why do I have poor environmental conditions? Answer: Now there is the real mystery, because when the parameters were measured they were "all perfect". Hmm...everything is perfect and yet the fish are sick?

I think it is all too easy sometimes to confuse the cause (environment) with the effect (sick fish).

Breaking out the ol’ Ishikawa diagram much?  Or should I say “Fishbone?”. 
 

Ok, enough nerd humor.  One of the big mistakes in life, not just the hobby, is seeing the symptom as the problem.  In the end you treat the symptom and the problem is never addressed.  

[Paul]

Many fish succumb to disease caused by stress. The stress can be aggression from tank mates or it be from the environment in the tank. The stress weakens the immune system and once that happens you’ve got sick fish.

Edited November 8, 2020 by Paul

[Ken Burke]

3 hours ago, Paul said:

Many fish succumb to disease caused by stress. The stress can be aggression from tank mates or it be from the environment in the tank. The stress weakens the immune system and once that happens you’ve got sick fish.

Good point, but stress can come from the environment or something external. 

[Maggie]

3 hours ago, Paul said:

Many fish succumb to disease caused by stress. The stress can be aggression from tank mates or it be from the environment in the tank. The stress weakens the immune system and once that happens you’ve got sick fish.

Stress also causes illness and greatly exacerbates otherwise mild diseases in people, too!!