Do water changes stress fish out?
Large water changes that include more than 60% water change, rinsing gravel, cleaning filter media lead to a complete, massive change in the water chemistry. Fishes when put in these new conditions, lead to temperature shock, stress, loss of appetite, and then death.
Once the panic has passed, the fish must also regain its natural balance. This can take hours or days, even after only a short period of stress. Long-term changes, such as a poor or unsuitable environment, are handled with the same initial response – an alarm message to escape.
Whenever more than one fish becomes ill or if you believe your water quality is poor, always perform a series of small water changes. Change 5-10% of the water once a day for 3-6 days. You should avoid large water changes because fish become accustomed to accumulated toxins in the water.
Though it seems odd, the truth is that fish can get stressed in much the same way as humans do. Whether it's a messy home, strained relationships with friends and family, or just general business, you can sympathize with a stressed out fish.
Gasping at the Surface: This is a sign of stress usually due to poor water conditions and not enough surface movement, so the tank is not receiving enough oxygenated water. Loss of Appetite: A stressed or sick fish will have a reduced appetite.
Here is the answer to Rebecca's question: In many cases, adding a little salt to a freshwater aquarium can help, as it reduces the stress on the fish by assisting the fish's osmoregulation (sorry for the technical term – what it means is it makes it easier for the fish to maintain itself physiologically in the water).
Fish can be stressed if they are not comfortable in their surroundings. Clear water with little surface coverage will cause a fish to feel insecure. The fish are more susceptible to predator attack in clear water and the fish is aware of this risk. Providing surface coverage or an underwater hiding place can help.
Light during the night causes stress to aquarium fish
Not turning off the light during the night for a longer period of time causes stress to all aquarium fish. In an aquarium we always try to make the circumstances as natural as possible. This is to give our fish the best possible conditions for them to live in.
“Fish do feel pain. It's likely different from what humans feel, but it is still a kind of pain.” At the anatomical level, fish have neurons known as nociceptors, which detect potential harm, such as high temperatures, intense pressure, and caustic chemicals.
Aquarium fish that are stressed or ill are unlikely to display their optimal coloration and they may even fade in color as a result of stress. In order to prevent this from happening in your tank it is important to keep up a regular maintenance routine to ensure high water quality.
What does a shocked fish look like?
Some fish succumb to pH shock immediately. Others may exhibit symptoms including thrashing, darting, gasping, swimming near the water's surface and trying to jump out of the tank.
A 25% change is a good partial water change. Check temperature, dechlorinate and pour slowly back into the tank, and you should have no problems. If there is an emergency like high ammonia and nitrite, change 50% on a daily basis until those levels have come back down.

Some fish can survive for a few minutes out of water, some for a few hours, and some for even a few months! This mostly depends on the species of fish, the habitat/environment, and how long you fight the fish.
Temperature – Tropical fish will become stressed if the temperature is consistently too high (above 29oC) or too low (below 21oC). A good heater will maintain aquarium temperatures at 24/25oC which is a safe level for the majority of tropical species.
Weakness or listlessness. Loss of balance or buoyancy control, floating upside down, or 'sitting' on the tank floor (most fish are normally only slightly negatively-buoyant and it takes little effort to maintain position in the water column) Erratic/spiral swimming or shimmying.
- Swim actively throughout the entire tank, not just hanging out or laying at the bottom, floating near the top or hiding behind plants and ornaments.
- Eat regularly and swim to the surface quickly at feeding time.
Common table salt is suitable; however, it should be non-iodized and contain no additives. Rock Salt or Kosher salt are excellent choices, as they are pure sodium chloride with nothing else added.
Fish are not as reliant on light as plants. In general, aquarium owners can use incandescent, fluorescent, or LED lights for fish but should be aware of the heat issues that incandescent lights cause.
A fish-only freshwater tank doesn't require lighting for many purposes besides illuminating the tank, and essentially any color spectrum can be used safely without harming your fish.
If you turn a light on in the middle of the night you'll see how still they are. Like people, fish have an internal clock that tells them when to do things like sleep and eat. So even if you accidentally leave the lights on at night, the fish may settle down and go to sleep anyway.
How do you know if a fish is in pain?
Numerous studies in recent years have demonstrated that fish feel and react to pain. For example, when rainbow trout had painful acetic acid or bee venom injected into their sensitive lips, they stopped eating, rocked back and forth on the tank floor, and rubbed their lips against the tank walls.
When fish experience nociception the neurons across their brain light up in response, showing activity that likely corresponds with a subjective experience of pain. Fish also hyperventilate and exhibit high-stress behaviors associated with pain.
Hooked fish struggle out of fear and physical pain, desperate to breathe. Once fish are hauled out of their aqueous environment and into ours, they begin to suffocate, and their gills often collapse. In commercial fishing, fish's swim bladders can rupture because of the sudden change in pressure.
Osmotic shock happens when the fish is unable to regulate its uptake of ionic compounds, which leads to too much absorption or too much release of fluid. Impaired osmoregulation then causes a condition known as dropsy, which leads to fish swimming erratically after water change.