the-knight-in-crimson:

“We had a monster where there were two forms of him. When you’re inside Rapture it would be more upright and have a more humanoid look to it. When it would go out in the water, what looked like its arms when it was on land became its legs, more or less and its fins, and that would propel it.”
                  -Colin Fix, Senior Character Concept Artist, 2K Marin

Early Aquatic Splicer Concept Art - BioShock 2 (click on images to enlarge)