How did the term "crayfish" become "crawdad"?

I am given to understand that "crawdad" and "crayfish" refer to the same creature (or group of creatures resembling small lobsters that live in freshwater), and that the difference is dialectical.

According to Wikipedia, "crayfish" becomes "crawfish" in parts of the US (1), but what brought on the "-dad" ending change?

Crayfish, crawfish, and crawdad:

• are interchangeable terms for a large group of freshwater crustaceans (not fish) resembling small lobsters and living in many regions throughout the world. Crayfish and crawfish are renderings of regional pronunciations of the same word, descended from the Middle English crevise (-vise became –fish), which in turn has Old French and Germanic origins.

• Crawfish is preferred in the U.S., while crayfish is preferred in most other English-speaking areas. Crawdad is prevalent in parts of the U.S., and cray is frequently used in Australia and New Zealand.

The Grammarist)

Crawdad:

• fanciful alteration of crawfish (Collins Dictionary)

• 1900-05, Americanism; craw(fish) + dad (perhaps dad); cf. doodad (Dictionary.com)