That is a sad sad site...
So sorry for your lost..
If i had to bet.. i'd say the fish's death wasn't caused by parasite or any form of bacteria... but its actually the bichirs...
Plecos and Bichirs dont play nice at all.. in fact.. i would never recommend anyone put the two species together... South American and African fish do not mix well.. Also, Bichirs have bigger mouth than Pleco.. they shredded fins on this L25 indicate that he's gotten beat up quite a bit..
FYI... if you ever come across a rare fish like L25.. take extreme care for it and dont mix it with anything non south american... Cichlids are fine unless its Red Devil or Midas.. those are just evil fish...
The second thing could be temperature.. I am not family with Bichirs temperature range.. but if water is TOO hot.. 86 and above.. it can lead to pleco suffocation, when water is too hot.. oxygen level to defuse must faster in water... I've lost a few pleco in summer months.. that why I make sure to turn off heaters by day and replug in heaters by night..
Well i dont need to tell you what a great lost you have.. but thats what i think caused your Pleco's death..