Better to stick with a cake.
This is a cake I made last year. Fish cake. No bones, no scales, just a cake and buttercream.
Haniela's Velvet Pound cake - 2 -9x13inch cake layers
Swiss Buttercream to fill and ice the cake
Marshmallow Fondant to cover cake
Gumpaste for the fins and details
PME Sugarcraft Lustre Spray - Silver - whole cake is sprayed with silver
Americolor Royal Blue Soft Gel Paste for the blue spots on the cake
Template for the fish, cut out from a piece of paper
Gourmet Food Writer Set, Black Marker to draw the template on the cake
Wood Grain Mat to make the cake board, cake board covered with fondant
Let's eat the Fish!