Cories might be breeding.

[TheJakeM]

I have two Cory catfish. I'm not sure of subspecies, but they are silver-gray, with a black stripe near their spine on either side of their body, going their entire body length, one is a little bigger and fatter than the other(maybe the female?). I have had them about 9 months so I figure they are a year or so. The smaller one has been chasing the larger one in the back of the aquarium, against the glass. Are they attempting to breed? I'll try to get some video soon.

[Old Scales]

SOunds like you have skunk corys. Watch the one you think is the female for awhile. After they go into the "bushes" and make whoopie, she'll swim all over the tank, many times going upside down against a plant leaf. Look very closely at her ventral fins. She will have them clamped together tightly holding her egg between them. Look very close for the egg. Its is pretty clear and kinda hard to see. They are really fun to watch spawn. I have Julie corys and my biggest female is a regular "love machine" she has been spawning with one of the males about every 3-4 days for two weeks now.
My happy little corys ara my favorite fish in the tank. Enjoy! OS.

[TheJakeM]

Originally Posted by Old Scales

SOunds like you have skunk corys. Watch the one you think is the female for awhile. After they go into the "bushes" and make whoopie, she'll swim all over the tank, many times going upside down against a plant leaf. Look very closely at her ventral fins. She will have them clamped together tightly holding her egg between them. Look very close for the egg. Its is pretty clear and kinda hard to see. They are really fun to watch spawn. I have Julie corys and my biggest female is a regular "love machine" she has been spawning with one of the males about every 3-4 days for two weeks now.
My happy little corys ara my favorite fish in the tank. Enjoy! OS.

Isn't it strange that it has taken this long? Or do you think they were too young before?

[Old Scales]

Could be they are just now getting old enough. I had mine about 7 months before she spawned and they were pretty big when I bought them. Alot of times an improvement in food(ie. frozen brine shrimp/bloodworms) and or a little drop in temperature after a water change will trigger a spawn. Kudos for being a good fish keeper. OS.

[TheJakeM]

Originally Posted by Old Scales

Could be they are just now getting old enough. I had mine about 7 months before she spawned and they were pretty big when I bought them. Alot of times an improvement in food(ie. frozen brine shrimp/bloodworms) and or a little drop in temperature after a water change will trigger a spawn. Kudos for being a good fish keeper. OS.

Thanks, the temp had a drop of temperature yesterday and today because we turned off the tank and house heating and didn't come home for about forty hours. Then, surprise, in the middle of May, in a week with temperatures in the 80s it got down to 45 outside. They have also recently gotten to a large, dead ramshorn snail, an earthworm, freeze dried bloodworms, and whatever else the other fish don't get to.