yeh variety is everything for a lion, and any fish at that matter.
best thing to do, considering you have the time to scoop out leftovers everytime you feed is to offer him about 3 different things at a time.
and yeh, well fed a lion can reach full size in just over a year!
all honesty, if you can get a lion onto frozen then they are a doddle to keep healthy,
get a silverside, chop of the head and scoop out the guts, stick about 4 formula 1 pellets in followed by some selcum powder, and soak that in garlic for 10mins, that is one of the healthiest meals a lion can have!
be careful with feeding live food as a present tho, one day he might take one and then refuse frozen!