Oto Diet

I got two small oto's yesterday and wanted to be sure they would eat flakes
if there weren't enough algae. I had what I now believe was an oto (larger
one) a month ago (the store had it labeled as an SAE, which it surely
wasn't). He was doing nicely for a couple of weeks and then he turned up
dead. I assumed it was from not eating as the day after I got him the tank
was clear of all algae. Maybe it wasn't starvation, I don't know for sure.
Anyway the guy at Petco says the flakes will contain spirulina and so the
oto should be fine with flakes (TetraMin). Is this true or should I get
algae tablets or other for them to be sure?

On a side note I was looking at a tank of oto's the other day. Some of them
had a black stripe down the body that was very straight and clear. Others
had kind of a black stripe but it was like there were black dots just above
the line and touching it, and the line wasn't as distinct. Is this a
male/female thing?

Thanks,
dwhite