A fish tank is a place in which to keep fish. Usually rectangular with glass sides. To "gen up" is to learn. To gain knowledge. Tropical fish are fish from the tropics. :)))))

To "gen up" is to learn about something, to get more information. "I've been learning about tropical fish, because I'm getting a fish tank next week." "I have an exam next week, so I've been genning up on grammar." "I want to import toys from China, so I've been genning up on customs duties."

下周我会得到一个鱼缸，所以我正在了解热带鱼。