Cold water fish like Goldfish, Orfe, Rudd and some species of catfish. I have left out Koi Carp on purpose because although they are coldwater fish they are also specifically for keeping in large ponds.
Sub-tropical and coldwater fish can live without heaters BUT you must note that just because a tank doesn't have a heater in it, doesn't mean it's coldwater! To have a true cold tank you need to install a chiller, which is far more expensive to buy and run than a measly heater!
Fish from all temperature ranges will be stressed out by temperature fluctuations (such as you having the heating blazing during the winter, and air conditioning during the summer!).
What fish you can keep also depends on your tank size. Goldfish are the most common coldwater fish, they also need very large over-filtered tanks. Smaller fish like White Cloud Mountain Minnows and Zebra Danios need to be in shoals in at least 15-20 gallons or more.
Research fish species very carefully!
Temperate and cold water fish. Minnows and goldfish, for example.
Fun fact, goldfish are not cold water fish. They are temperate; meaning they can handle a wide variety of temperatures
Tropical fish.
Typically heaters are needed for tropical fish tanks. However, if you could guarantee the room temperature where the tank is located will be maintained at the needed temperature for your fish, then you don't need a heater. Most tropical tanks need to be maintained at temperatures of 72 to 80 degrees Fahrenheit, depending on the types of fish in the tank.
Blood parrots are tropical fish, yes they do need heaters.
No. Depending upon the climate you live in, tropical fish may need heaters if you live in a cool place and if you live in a warm place cold water fish may need coolers. Each species has its own requirements.
its for tropical fish and salt water fish. they need to have warm water to survive cause were they live is really warm waters
No
Betta fish do not enjoy currents that come from filters. You could put in a filter but I would recommend not to. Also, Heaters are unnecessary as long as you keep the water 70-80 degrees.
guppies
You need to specify who 'they' are.
no some dont need air like fish dont they need water
i dont think so
Yes but star fish are asexual so they dont need a partner