Crushing human pellets is not a good idea because you don't know how well it was mixed when manufactured. Which end has the vitamin C, which end has vitamin whatever? There are warnings on human pills that say specifically not to use part of the pill. Because most of it is filler and combining agents that make the pill large enough to handle and hold it together.
There is no way for you to know what chunk is inert filler and what is pure medication.
Giving a small part of the pill does not mean you are giving a small dose.
Sure vitamins are good, in the correct amount. But if you do a little research as to how they are used together in a balanced way you will see the dangers of even small over doses of any one type.
I would not give a (relatively) small fish medication that was meant for a 200lb human.