Prospex for Seiko basically means "Professional Specification" that their timepieces in this category  are built with very high standards to be used by professionals. Seiko introduced the Prospex 200M Automatic Baby Tuna under the Prospex collection means it fulfills the "Seiko Professional Specifications".

The Baby Tuna got its nickname from its resemblance to the Marine Master Tuna.  Powered by Seiko's automatic caliber, 4R36, operating at 21,600 BPH (3 Hertzs) with hacking and hand winding capabilities. It has 24 jewels with a power reserve of 40 hours.