How stressed does a fish have to be before it dies?

[supersam]

How much stress causes a molly fish to die? What are signs of extreme stress that may lead to death?

[bahari]

I would say any rapid changes could cause fatal stress. Depending on the stress, the fish might be submissive or aggressive. Fish’s immune systems lower when they are stressed, so it might become ill. If you notice a stressed fish, try and move it to a calmer situation and away from whatever is causing the stress. If it’s just moving into a new tank, wait it out.

Hope this helps!!

[Caliban07]

Cortisol is an indicator of stress. It is found in the blood and it is released as a response to stress).

If the stress is persistent and of sufficient intensity, changes in the cellular structure of the gills may occur under the influence of cortisol. In this situation, increased death and turnover rates of branchial epithelial cells leads to accelerated aging of the gills. These degenerating and newly formed gill cells do not function normally, which further limits the fish’s ability to maintain water and ion homeostasis under stressful conditions. Thus, acute stress limits the fish’s capacity to osmoregulate, and prolonged periods of extreme stress may result in osmotic shock and death. (Joe Gargas Aquatics magazine 2011)

Rapid breathing is a sure sign that the fish is stressed. Erratic movement and twitching etc.

Rapid dissolved solid fluctuations (depending on ions involved ) caused acute and/or chronic stress.

Bullying causes stress and cortisol release and will likely show through with rapid breathing.

[gilpi]

From my own failures I have learned throughout decades that the visible signs of stress are rapid breathing, breathing on the surface, hiding and no appetite. These are some of the earlier signs. Main causes are usually water conditions (in general) and or bullying by other fish.