A 3D model of a Tuna fish in the style of Minecraft. The model should be blocky, low-poly, and constructed from visible cubes and rectangular prisms, as if it were made in Blockbench. It needs a simple, clean topology suitable for a game asset. The texture should be a simple, hand-painted pixel art style, with dark blue on top and silver on the belly. Render on a plain background, isometric view.