Create a basic animation to show the fish tank animation :-
1.Open a new document & in this go to the modify-document & set background color blue.
2.Insert a new layer1 select the layer & draw or take the fish on each separate layer.
3.Select all fish layers & select allframe1 head & right click on frame1 & select create motion tween then select frame 60 & drag from first layer to 4 layers of fish & then press f6 (insert key-frame).
4.Select the first fish layer & click on any frame in between 1 to 60 & pressf6 (insert key-frame) & then change the position of fish as per your choice.
5.Does the same procedure on each fish layer i.e. click frame press f6 & change the position of fish.
6.Take the new layer for grass & other material & on this layer take or draw the grass or another plant.
7.Take another layer for bubbles select this layer & draw the bubble from the oval tool at this time stoke & fill color option should be white then select the oval & go to the fill color option & switch of the color & using brush tool dot or mark on the oval then select the bubble layer.
8.After selecting the bubble layer click on frame1 & right click on frame1 & select create motion tween & then press f6(insert key-frame)
9.Then select any frame between 1 to 60 frame & press f6 & change the position of bubble do the same procedure(i.e. select frame, press f6 & change the position of bubble)
10.Then take another new layer for new bubble & do the same procedure for bubble
11.Save your work & test the movie.