Hmm - the Google-translated version of that page says that Russian POWs in the Russo-Japanese war used salmon roe (i.e. ikura) as a substitute for caviar. Interesting—thanks!
It maybe makes a bit more sense when you consider 'икра' doesn't just mean caviar but alsо fish roe in general and is also applied even more broadly in entirely fishless things like 'икра баклажанная'
