How to get a petfish.
Requirements: 42 crafting
Items needed: glassblowing pipe, bucket of sand, soda ash (cooked seaweed), seaweed and 10gp. (if you take you bucket and a glassblowing pipe to Entrane you can find the rest there...)
1.Use the bucket of sand with a furnace, you know have molten glass (your soda ash is now also gone).
2.Use your glassblowing pipe on the molten glass and make a fishbowl.
3.Go to a water respawn and use fishbowl on it. Now use your seaweed on the fishbowl.
4.Go to Harry in Catherby and talk to him, he will now sell you a tiny net for fishing his aquariums. Fish there and you now got a pet fish!

Things you now can do with your pet fish
You can talk to him, play with him and feed him.
Talking to him and playing:
Right click on the fishbowl and choose "talk-to" or "play-with"
If you now click on play-with he will trow the bowl up and down which is quite funny...
Feeding your fish.
Talk to Harry, ask about how you should feed him. He say he doesn't have any fish food in stock but he does have a empty box. Read the box and it will say that to make fish food use a guam leave and seaweed on a pestle and mortar.
You can also just get some fishfood from Draynor Maynor and use it on your fishbowl, the fishfood is now "an empty box"
Faqs:
-You have the colours: Blue Gold Green Red
-You also can have a spined fish
-Once you drop the Fishbowl, your fish will die!
-You can have as many pet fishes as you want.
-But you can only have 1 in each fishbowl.
-The tiny net is also a monster drop from river trolls
-The tiny net and the fishbowl are untradeable