that looks remarkably like eus (Epizootic Ulcer- ative Syndrome) unfortunatly if it is there is no hope for the fish as it results in 100% mortality , i would get that lima into a hospital tank just incase as it is highly infectious , useally theese catfish are not the primary carriers though ,so what other fish are in with him?
do you have any of the primary carriers in with him ? of course if you havnt had him that long he could of contracted it in his last tank
primary carriers :
Atlantic menhaden* (Brevoortia tyrannus)
ayu* (Plecoglossus altivelis)
bagrid catfishes* (Bagridae)
barramundi* (Lates calcarifer)
carp* (Cyprinus carpio)
cichlids* (Cichlidae)
climbing perch* (Anabas testudineus)
cyprinids* (Cyprinidae)
eel* (Anguilla australis)
flathead gobie* (Glassogobius giurus)
giant glassfish* (Parambassis gulliveri)
giant gudgeon* (Oxyeleotris sp)
grey mullet* (Mugil cephalus)
mrigal* (Cirrhinus mrigala)
mullets* (Mugilidae)
pool barb* (Puntius sophore)
rhinofishes* (Labeo spp)
rockcod* (Epinephelus tauvina)
silver perch* (Bidyanus bidyanus)
silver trevally* (Psuedocaranx dentex)
gourami* (Trichogaster pectoralis)
snakehead* (Channa)
torpedo-shaped catfishes* (Clarius spp)
triangular shield catfish* (Arius leptaspis)
tropical two-winged flying fish* (Exocoetus volitans)
wels catfish (sheatfish)* (Silurus glanis)
whiting* (Sillago ciliata)
yellowfin bream* (Acanthopagrus australis)
archer fish (Toxotes chartareus)
blackfish (Platycephalus fuscus)
Froggatt's catfish (Cinetodes froggatti)
nurseryfish (Kurtus gulliveri)
scat (Scatophagus argus)