P stands for:

Acipenser Persicus is a species of sturgeon closely related to Acipenser Gueldenstaedtii, of the Ossetra family, found only along the Iranian coast of the Caspian Sea. Its grains were particularly golden and its caviar was often listed as “ossetra gold”, with its unique taste.

An Iranian speciality, this fish loved the warmer waters of the south and contributed to the prestige and glory of Iranian caviar.