How many degrees does it have to be for tropical fish, gold fish, bettas, and cichlids?

Question

I know each one is slightly different

Answer 1

These can be quite different depending on the exact species. Tropical fish, by definition, should have water above 76oF. Most fishkeepers use a range from 76-80o although there are some that like it even warmer, but others, such as guppies and danios can survive at temperatures to around 70. Goldfish prefer the water cooloer, with 65-70o being the best, although the can tolerate warmer tamperatures if there's enough dissolved oxygen. Bettas do well from 76-86o. Cichlids are more variable, but most would do okay in the same temperatures as tropicals, up to the mid 80s, but others (discus in particular) should have the water into the mid 80s. If there's a particular species in which you're interested, you can look up the conditions recommended in any of these links:
http://www.elmersaquarium.com/000tropfishcareguides.htm
http://www.fishprofiles.com/profiles/default.aspx?pnl=fresh
http://www.liveaquaria.com/

Answer 2

The truth of the matter is that each of those fish can live in a fairly wide range of temperatures and most overlay quite a bit.

Basically you can separate fish into to groups, tropical and coldwater. Coldwater fish are able to tolerate temperatures far lower than tropicals.

Goldfish are the most common example of coldwater fish and do well in temperatures from the mid 60's through the upper 70's, but can live in water so cold it freezes over or in temperatures into the 90's for a short period of time.

Tropical fish however can't stand such cold. All of the fish you list other than goldfish are considered to be tropical and all will do well at about 76-82F but can tolerate temperatures from the upper 60's to the high 90's for short periods of time.

MM