Reducing drawcalls on texture atlas animation

I have made a very simple animation of a fish on Maya that I have imported into Unity. It has a spline IK handle and in maya it has 170 vertices and 230 UVs. BUT when I bring it into Unity it appears to have 25.6k vertices ( is that really 25,600 vertices ?) And for some mysterious reason I am pulling 100 drawcalls and I dont know why. I have a floating GUI button above it that activates a selection from 25 materials that are using the same texture atlas that has 25 different textures on it ( Max size 1024 dxti compressed ), one directional light, and 100 draw calls.The only thing I can think that is making that much draw call is that I have this ONGUI script on the fish

function OnGUI() { if(GUI.Button(Rect(screenPos.x-100,Screen.height - screenPos.y-50,200,150),"",customButton))

     renderer.material= materials[Random.Range(0,renderer.materials.length)];

}

The only way I can get it to work is if, in the inspector, in the skinned mesh renderer,I have the 20 materials listed, and then the 20 materials listed in the script. I thought >I should be able to just have one material listed in the skinned mesh renderer and then change materials but it doesnt seem to work that way. I also tried to change the script to

renderer.materials[1]= materials

but it doesnt seem to do anything. Any ideas how i can reduce my drawcalls ? It seem like a lot for an empty scene with just one small fish swimming around..