Once you decide on how big you want your fish bowls to be, use graph paper to draw out the pattern. Once you have it drawn out, cut your pieces out on the lines and add 1/4 inch seam allowances to all sides and you have your pattern pieces. I myself would probably enlarge it to make a 8 inch bowl and use squares to "snowball" the corners to make the triangles. To "snowball" you lay a square on the corner and sew across the diagonal line from corner to corner. You then fold out the square to form a triangle and trim the back extra fabric off at the 1/4 inch seam allowance. Here is a drawing of how I would start.
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