Ikura can mean two things. In the
hiragana alphabet, which is the alphabet for sounding out words of
internal Japanese origin, it means
how much. In the
katakana alphabet, which is the
alphabet for sounding out words of
foreign origin, it
refers to
salmon roe.
The word ikura in
reference to
caviar comes from
ikra, which is the
Russian word for caviar, of which their caviar is often none other than salmon roe.