here is a finished mid-poly fish. Over all it took me about 3 hours total. The blend includes two packed images; the ocean background, and the texture of the Tang, and a mid-poly model of the fish with a simple full rig included. Both the background and the fish have a shadless render built into their node sets, and if you'd like to remove it, just delete the mix shader, the light path, and the emission, and add the defuse with the image input.
If you have any trouble with the packing, or anything else, please let me know, and I will fix it. You may use the lovely fish as you please. I will be soon modeling an Achilles Tang as well in a separate blend. Thanks for reading!