Are these parasites on my Bolivian?

Just to detail the tank etc.

125Ltr Heavily planted.
Inhabitants are 4 adult pitbull plecs, 3 Otos, 8 Cardinal Tetras and 4 Bolivians.
Temp 25-27ºC (dependant on the summer weather at the moment, heater is set to 25)
Ph 6.4 - 6.8 (Co2 injected due to the plants)
Ammonia, Nitrite both 0 (not tested but overfilteing and plants will mean zero.)
No idea on GH/KH
Nitrate, Phosphate, Potasium and traces added daily but to a low dosing regime (again for the plants)

OK so on to the little problem. I have added a pic below of what look like parasites on my Alpha male Bolivian Ram's vent area. The Beta male also has these to a lesser extent in the same vent region. Both Alpha and Beta Female have nothing like this. It is just the 2 males. Behaviour of the fish is unaffected. Both are feeding as aggressively as always (I put 1 full frozen cube of bloodworm in each day which all 4 Rams do battle with.)

So do I have a problem here or is it just a natural thing. I assume it a harmless thing if it is a parasite due to the fact that they are both behaving normally. There is no flashing going on.

I have been running a course of Sterazin just in case. Now on day 10 of the 15 day course.

Many thanks in advance for any help.


Andy