Aha, it was (still is) called "ryibiy zhir" ("fish fat"),- i was given it too when i was little, because ALL parents were compelled (by so-called therapists), that kids need these fish fat capsules to get Omega fatty acids and other vitamins. As a soviet kid, you simply couldn't avoid it. But it wasn't always like that,- it had been worse. In the 60th, it (fish fat) was in a liquid form only. E.g. my dad had to swallow this gruesome liquid as it is. Bleh... Luckily, i avoided that fate: in the 80th, capsules appeared and i had to devour those capsules. But i hated them anyway, because their taste was still impressively repulsive, even from the outside (plus they were stinky). It was nauseating.
It was given to children to prevent rickets. Nowadays, it is given in the form of liquid drops: