Feeding Ottos

Question
Hi Will:
I'm hoping this question is one for you.  I am not new to freshwater aquariums or ottos, but I had something happen today that has me scratching my head.  I usually give my ottos romaine or red peppers as a supplement.  Today I put in avocado, I have done this one other time in the past with different ottos.  I've had these for 6 months and they are very healthy little chubby gusy.  Today I put in the avocado and within 2 hours both of them were dead.  I am devastated and confused.  Do you happen to know if this is a toxic veggie for them?  I'm sure I've read it was an OK food, but now I can find nothing online about it.  I feel awful and negligent and am hoping someone can shed a little light on this for me.  My guppies were eating it like mad and so far all of them are still fine as are my neons.  This was about 4 hours ago I found them. Ammonia 0, PH 8.0 (it's been that for about 3 years now)Nitrate 0/5, Nitrite 0.  Last water change was about 20% about 5 days ago.  I do them weekly.  Thank you so much for your time.tw

Answer
Hi,
I wouldn't be surprised if a few of the ottos had an allergic reaction to the avocados. I know many animals including dogs and some types of fish cannot eat them, so whatever is in them that makes it so may have had an effect of a sensitive individual. My final idea is that there were some bacteria in the fruit the fish may have eaten.