Internal parasites question

[BettaMomma]

A fish can be badly infested by some sort of internal parasite and not exhibit any physical signs of illness (aside from lethargy, clamped fins, laying around, etc.), correct?

Basically, their body can look perfectly normal but they can still be infected, correct?

 

[WILDER]

Signs of interna parasites are long white stingy poo, red inflamed anus, a worm protruding from the anus, bloating or looking thin, also sunken in tummy.

 

[Henry_VCG_]

What about the gills? Can they appear deep red?

 

[WILDER]

Red gill can be high nitrites,gill flukes, irratation, old age.