When it comes to tropical fish, many people may think of colorful fish found in the sea around Okinawa. People who know a little more about tropical fish may think of such species as angelfish or guppies. When Japanese people talk about tropical fish, we often think of the freshwater fish of such tropical areas as Southeast Asia, Central and South America and Africa.

People in Japan say "The water is not suitable," because some freshwater tropical fish from other countries soon die when suddenly forced to live in Japanese tap water. But in practice, the fish are transferred from their native waters to a water tank for transport, then to a distributor, then to a pet shop, so they gradually become acclimated to Japanese water. By the time they arrive at people's homes, that can be kept in tap water or well water.

Some hard-core fish hobbyists use different tanks for different types of fish and measure the conductivity of the water, controlling pH and water hardness to best suit their fish. But really there is no difference between keeping tropical fish and goldfish with the exception of controlling the water temperature at around 25 °C.

Some years ago, we measured the conductivity of water in tanks at a pet shop, and it was 0.2-0.6 mS/cm in most of the tanks, but 5-10 mS/cm in the tank for guppies. We asked the owner about this, and he told us that when guppies were transported from their place of origin to Japan, they were sometimes shipped in salt water to maintain their beautiful colors, and that if they were suddenly placed in fresh water, they didn't seem to feel well, and hence salt was put into the fish tank as an experiment.

You would not hear this kind of a story from many pet shops, so if you are seriously interested in keeping tropical fish, try to chat with people at a pet shop and pick up what knowledge you can. If you can get valuable information from a pet shop, you'll know you're in the right pet shop. anyway.