Russian Sturgeon (Acipenser Gueldenstaedtii) roe is used to produce one of the world's most well-known caviar. Any caviar connoisseur will instantly recognize the word Osetra when they hear it, but they might not spell it the same way we do.
Osetra is widely used when describing caviar from the species of fish known as the Russian Sturgeon. Sometimes called the Diamond Sturgeon, Danube Sturgeon, or Osetra Sturgeon, these Caspian and Black Sea dwelling specimen were often caught in Russia. Thus, it is widely believed that the name given to Russian Sturgeon caviar simply came from осетр (osetr), the Russian word for sturgeon.
Osetra, Ossetra, Osietra, Oscietra, or Asetra are all spellings used to title the roe from the Russian Sturgeon, and the different spellings of the word were actually created from the producers and sellers of Russian Sturgeon caviar in different parts of the world. None of the spellings of Osetra are incorrect, some are just more accepted than others depending on where you are.
Osetra and Ossetra seem to be the most widely used, especially in countries where English is spoken as the primary language. Osceitra, Oseitra and even Asetra are more commonly found in other parts of Europe and Asia, but there is no standard dictionary spelling for the word in most languages. In the English language, the Merriam-Webster Dictionary has it down as Osetra, so we'll keep it like that for now.
Caviar companies today can choose whichever "Osetra" suits them regardless of how it is traditionally spelled in their region. This makes it even more difficult to pinpoint exactly where the changes in spelling come from, and can often make buying Russian Sturgeon caviar more complicated than it needs to be.
Whether you're buying a container of Asetra, Osetra, Ossetra, Osietra, Oscietra, or осётр, it is important to remember that all these words simply translate to sturgeon. This means, no matter how it is spelled, you should check that the caviar you are getting is from the Acipenser Gueldenstaedtii species rather than from "Osetra". There are caviar sellers that will use the name Osetra to trick customers into thinking that they are buying Russian Sturgeon caviar when it is actually caviar from a lower-cost species.