A Runt Goldfish

Question
I have a 20 gallon tank impeccably clean. I use cycle, waste protection, and Aqua Plus. I feel I am very educated about my fish and have brought them back from sickness but this boggles my mind?

I have 1 fish whom I got with the rest of the tank of fish. All the fish in the tank right now are huge, I mean HUGE! This is probably due to my cleanliness factor.  However, this one little guy won't grow.  First of all, he has to be in distress as there is some light black streaks on the back of his bottom but are very difficult to see.  He/she is terribly underweight and spends much of his/her time by itself at the top of the tank blowing bubbles and not eating.  I watch it when I feed it and it either eats 1 or 2 clumps of food, and even though it is relatively tiny, it chews it up and spits it out and after the 2nd attempt just continues to blow bubbles and the rest of the food gets eaten by the rest of the fish.  I know its not insepticemia, checked it.  And I know that it can't be a fused mouth or partially fused mouth because it's mouth appears wide enough enough to blow these huge bubbles and it's mouth size seems no different from the rest? I wondered if it was an oxygen factor but all the rest of the fish seem fine?

Sighed Curious?

Answer
Hi Keefe,

Very strange, it could be an oxygen factor. Goldfish are paricularly prone to oxygen deprivation. The surface water should be kept constantly churning to promote optimum oxygen exchange. The problem with modern tanks is they have a tendency to let oxygen levels drop too low. Equipment to test Saturated oxygen is either very expensive or totally inaccurate. However it might be worth getting it checked out. Oxygen levels should be at 8 but never lower than 5.5.

Emaciation is usually a symptom of the following:

Hexamita
Icthyosporidium
Internal Parasitic Worms
Neon Disease
Velvet Disease

Black markings would suggest either Black Spot or Clinostomum.

Is he swimming unevenly or displaying erratic behaviour other than blowing bubbles?

Tom