You will only know about the pregnancy of catfish about its size because its stomach will look bigger than before and she will behave differently.
How Do I Know If My Catfish Is Pregnant? He Has A Really Big Stomach.
If its stomach is getting bigger then there are higher chances of its pregnancy. It will try to clean the rock before actually laying eggs. You will notice that it will go to male and move its mouth towards male's anal fins. After a while it will lay eggs. It will take about three to eight days to hatch. Put heater, sponge filter and air stone in the filter. Best of luck.
You will know because - look at the size of your catfish. If your catfish's behavior has changed something is about to come. For example - if he/she was scared of a Oscar fish she will change by getting by it and being round it. Now you should know if your catfish is pregnant.
1st of all is it a he or she