Stress on fish is one of the major factor responsible for their short life span, breakout of various diseases resulting in death of fishes. Since fishes are in captive there is more chance of stress as compared to wild condition. Stress decreases the immune system of fishes and they loose their natural tendency to fight against pathogens. It is observed that stress causing factors are basically created by the owner of aquarium. So it very important to decrease stress.
Reasons and ways to reduce stress:
1. The most common stress causing factor is the water quality. When quality of water becomes poor, there is more chances that your fish get stress. Water quality degrades after passing of time because of increase in ammonia level because of waste products produces by fishes and extra waste food. So do partial water change of about 40% in week and don't overfeed your fish.
2.When some one purchases a fish from aquarium dealer and transfer it. During the time fish may suffer from stress. Because fish may got scare because of outer world. So put her in plastic bag then in dark bag.
3.Add slowly plastic bag to tank so that sudden temperature change doesn't occur. Then add fish.
4.Over populated tank may result in stress so keep only required number of fishes. The number of fishes can be calculated, you can put 1 inch of 1 fish in per gallon or 4 liters of water. Example if you have 2 fishes whose size are 2 and 3 inches then you require 5 gallon aquarium.
5.Sudden change in pH or temperature of aquarium may result in stress, so use aquarium heater wisely and make sudden change in aquarium heater efficiency.
6.Lights are also major factor don't keep on lights 24 hrs a day. Try to maintain as normal as outside.
7.One of the most important way is to provide lot of hiding places in aquarium.
8.Try to provide water plants to aquarium fishes.This also helps in decreasing stress.
9.Also provide good nutrient diet rich in protein and vitamins to fishes. This also decrease stress and keep them healthy.Also provide live food to fish who are omnivorous.
10.Avoid scaring of fish by children, surrounding change and movement of water roughly.
11. Compatible tank mates, otherwise they will chase each other and increase stress.
12.Some fish likes to live in group like rosy barb etc so keep them in groups.
By following above points you can decrease stress to great extend.