The flavour of caviar changes depending on several variables. It is possible to buy wild caviar which would be hackleback in the US and is generally approved for a set amount of fishermans quotas from the Tennessee to Missouri river. Processing also plays a part in the taste of caviar, as the most natural way of preserving it woud mean it is malossol, which has salt and eggs in the tin only. Most all of the caviar in market today comes from farms throughout the world. Some are land based in above and below ground tanks, called RAS or Recirculating Aquasystems and some are in cages in the rivers or in ponds or a flow through water system. What this means is that the water affects the flavor as well as the feed.
Caviar should always be a fresh taste, with ageing comes some depth of flavors like butter, nuttiness and the like. As there is so much in market, sometimes buying general caviar without knowing from where it was from or how long its been ageing can present a good or bad experience depending on its provenance and how long it was stored. Fishiness is not a complimentary flavor.