One of the most important factors of a healthy aquarium is to make sure the fish is healthy before you buy them. It can be as simple as watching fish before they are added to an aquarium.

– If you have sick fish in your tank, don’t add any new fish until cured

– The fatter the fish, the healthier it is

– Pick the fish that always pick a fight with others

– A healthy fish should include the following characteristic:

• arisen fins
• vivid colors
• sharp eyes
• swimming around
• energetically
• curious and react  to the surrounding
• always pecking and looking for food
• no sign of visible diseases such as white dots or cloudy eyes
• breathing evenly
• pooing

– Don’t buy fish which

• stay at the bottom or in the corner of the tank
• breathing difficultly
• has a wound
• missing fins  
• loses its balance while swimming  
• scraping rocks or sand