Common betta

Hi Xiaoxuan, I've moved this to pets for you.

Oh, perhaps you could pass on the information to your friend. If you haven't done so already you could add your Discus as a spotting.

Meant to say need a heater for the tank too.

Your betta in the photo looks very ill. Pet stores commonly tell people they live in puddles in the wild, this ony happens if there is a flood and they get trapped. They live in flood plains and area of calm water that have flooding, but these are about a foot deep at least and spread for miles. Captive bettas should be housed in no less than 5 gallon. They are tropical fish which means unless your room temp is in the 80s all year you need a filter around 78-80 F is ideal. You'll need a slow moving filter as that long finnage will not allow the betta to compete against a fast current. They like to hide among live plants, and for food they enjoy hikari betta pellets (mabye 2-3 a day only a bettas stomach is the size of its eye!). They love frozen bloodworms,daphnia, and brine shrimp. Although this this isn't a wild betta, people are misinformed about how they live in the wild, thus many pet bettas die from neglect, it's always important to do research before buying any pet.