Lots of ways, click on you or your friends treasure chest every day. Either right click on your fish and play that game, or click on the treasure chest at the bottom and then click on a fish and play that game. Sell your fish or items.
you can't
mate your fish for coins or pearls
If you buy and sale fish for a long time you can get coins
you have to waste all your food and coins
Now the Happy Aquarium store is offering blue male squids for 623 coins. It is under the Special star tab. You can mate them for 312 coins. You cannot adopt them, only buy.
you get get more coins by doing1- login to happy aquarium everyday and click on your chest and your neighbor chest, try add more neighbor as much as you can the more neighbor you had the more coins you will received daily.2. get your fish up to adult, then sell it for some profit. you may check the profit list herehttp://www.yayeasy.com/happy_aquarium/happy-aquarium-fish-details-and-profit/they are also updates a lot of info regarding happy aquarium. hope it can help you
You have to collect coins from your friends tanks. You will sometimes get a shell. Not always.
No its more for looks
The UFO is an accessory. You need 350 coins to get it in the props section.
You can only send food or gifts. For your neighbors to collect coins from you, they must visit your tank and click on the chest.
125 is the maximum tank size
When they are sick all you do is click on them then click heal. To heal them the cost is 5 coins. It's worth it.