Fish are one of the animals that you can keep as pets.
They do live in aquariums if being held as pets. In the free nature, they do live in sea's, big pools of water, and etc.
There are many types of fish. Some may eat others,
some need to live on their own and some can live together.
Female fish are mostly calmer then male fish.
In the nature, they do eat coral, smaller fish or anything of food they can find.
In an aquarium, they might eat special made fish food. The food is also based on the type of fish. Cold water and Warm water fish. For Cold water fish like the Goldfish, you should buy a pack food with category 'Cold water' or 'Goldfish' . For Warm Water, you should do the same but with 'Warm water' or 'Guppy'.
In a pack of food, there are different colors. Each are made from different food ingredients to keep your fish healthy.
There are many different known fish species.
Warm water fish do need between 20-24°C or 68-75,2°F . It should also depend on type fish, so, first search what species. There it should recommend it.
Cold water fish will need temperatures of tap water, but better look for their temperature respectively.
Guppy's are basically one of the best warm-water fish to start with. Goldfish are the best cold water starter-variant.
The aquarium/tank/water pool's size should also depend on the type of fish. 5 gallon tank is already very nice for guppy's, but they should have a 25 gallon one to feel on their best.
For a goldfish's tank, don't put it in a vase. Goldfish won't gain enough oxygen and might die. It should also have a 25 gallon tank or higher. A water pool is the best option. So can the Goldfish max out to it's biggest size and on it's healthiest. Another fact of the Goldfish is that it's organs keep growing in a small tank. So it might die too, as it's organs keep growing compared to it's body.
Betta Fish/siamese fish: Those are warm water fish but are better to live on their own. They are true fighters and might kill the other during a fight. Keeping two in each other a different tank is fine. Also, don't put guppy's or any fish on that size with a betta. They might eat it's small fins or even the whole fish. Only with pure luck your betta won't eat your guppy(s).
When sick or unhealthy, it's belly will get bigger and white or white spots appear on the fish. Also other noticeable things will happen. If that's the case, make sure too:
-Check the temperature of your water
-To clean your water
-search what could've made your fish sick.
-If you gave it too much food, it will be unhealthy. Some fish like the goldfish spew the food out as a noticeable action of 'you gave me a bit too much' .