Pleco Imploded?
 

Hi,

We woke up this morning and it turned out that the oxygen pump in our 50 gallon tank burned out at some point during the night, and the fish were without oxygen for a while.

We created a waterfall from the filter outlet, hopefully it will be enough till we go and buy a new air pump.

One of our 4 4 inch plecos though... HE'S DEAD!

And it's so weird! He looks like he'd imploded, his eyes are all sucked into the skull and the little symmetrical bristles on the head are also sucked in, his stomach is sucked in as well and ripped open as a result.

What happened? Looks too much of a death for a few hours of low oxygen.

At first we thought it was our blood parrot chichilds (very aggressive) who did it to him, but there are no bites and they weren't around him at all when we found him.

What just happened?

Thanks in advance

Pleco tank parameters
 

Here goes: 50 gallon, 5+ gallon canister filter, temp around 27-28 degrees celcius, oxygen pump, heater.

Fish:

3 (used to be 4 :( ) COMMON plecos - around 4.5-5 inch each
5 grey sharks (not sure what's the proper name for them, maybe shark catfish or something) - 5 inch each
4 blood parrots - 3 of them 3 inch, 1 biggest male - 4 inch
2 flowerhorns - 4.5 inch
1 oscar - 5 inch

moderately planted, 1 big rock

PH around 6.5, everything else within norm except nitrates - a bit high.

Thank you