Goldfish pregnant?

Question
I have one black goldfish and two gold koi (i think). The black one is bigger than the two and after I changed the water in our acquarium, i've noticed that he/she (can't tell) has this white protrusion behind his/her back fins. The black fish also is plumper than i remember from a few weeks back. We haven't changed the water in a while before today - almost two months, so i'm wondering if the fish is ready to give birth or is it sick? Also the fish is covering it's protrusion with its black fins and not using them much to swim. What's going on? Should we be expecting fry? I've noticed that the gold fishes are sort of biting the black one. Does this mean they're mating?  

Answer
Hi Evelyn;

The water change has put them "in the mood" for breeding. It simulates a spring rain that triggers their hormones. The black one may be a female and the others males, but if she is having trouble swimming it may mean she is in distress. Attempted spawning can be very stressful for females. Having waited so long for a water change may have weakened her too. Males will mercilessly chase and nip her vent until she lays her eggs so the males can fertilize them. Goldfish and koi are egglayers so you probably won't see babies anyway. The only chance for that is if they spawn and some of the eggs survive to hatch. Hatching takes three days or so after laying. In indoor aquariums the eggs are usually eaten and babies never hatch. In outdoor ponds where goldfish are usually bred there is a lot more area for the eggs to be laid in plants where the adult fish can't easily get them. There are many more places for babies to escape and hide safely too. Most aquariums are just too small to allow for that. Goldfish get big and just to thrive without breeding each fish needs 10 gallons all to itself. If your tank is smaller than 30 gallons you will need to upgrade.

It's actually okay if she never has the opportunity to lay any eggs she has inside her. She needs to be safe and healthy most of all. She will re-absorb the unused eggs back into her body. It would be best to get her isolated to another tank so she can recover from her stress. Keep her water clean and add aquarium salt to her water. You can get a box of it at your local fish store. It works as a general tonic, disease preventative and replaces lost electrolytes. All goldfish also need at least a 25% water change every week to thrive. A change of diet would help her absorb the eggs too. Give her cooked and peeled green peas instead of her regular food for a few days. Peas act as a laxative and will help her feel better. Goldfish commonly become constipated and it would become a very risky situation for a fish in her condition.

Let me know how it's going. I hope she feels better soon...

At Your Service;
Chris Robbins