Yes, I think water changes can induce birth and spawning. I've noticed this over the years with my guppies and with corydora catfish. It is almost like clockwork. The catfish in particular would lay eggs within 24 hours of a water change if it was in spring. With the guppies I'm not sure I would call it stress. They are so prolific, it probably just helps things along.

I have a 46gal bowfront. To prevent the babies from being sucked away during a water change I took a piece of plastic electrical conduit and bent it and shaped it (kind of into a "u" shape) using heat so that one end extends into the tank to the depth of the water change, and the other hangs out of the tank (I put a hose connector on this end so I can connect a water hose to drain the water). The end in the tank has a foam "strainer" on it (the foam is a cylindrical shape you can buy at pet stores). I use a small electric pump. ANyway, with this set up I can start the water change, walk away from it to do other chores, and I don't have to worry about the fish being sucked away or the tank becoming too empty. I haven't had to do a complete tank water change in several years now. And I haven't lost any fish due to suction. Oh, and I've had the same family of delta guppies for 38 years now.
-Hal

I've notice the same thing happens with my angelfish - they'll lay eggs soon after a water change.

hald, what a cool idea! congrats on the longevity of your line!

i definitely agree on spawning...fresh water does wonders.

can someone correct my info....? i thought when guppies were black on the end that was their gravid spot and were about to give birth. is this the other way around? my orange guppy was "clear to orange with specks (eyes?)" back there and she is the one who has lost girth, not my half black with the black splotches in "the rear." i know, i need to do a search but i am being lazy.
thanks!

The gravid spot can look clear with black spreckles on some types of fish. I think what you are seeing and describing is normal. Be sure and put something in your tank for the babies to hide in. Also, be sure and feed your guppies enough and they won't eat the babies. The trade-off and balancing act is food versus water changes - too much =more water changes.

If I had to advise I'd say always lean towards too much food in a guppy tank. They are tough little fish. And they will not overeat, no matter what you may have read elsewhere. They will also come to associate you with food and it is very nice to see them coming to greet you as you walk by the tank.

When your guppie family gets bigger you'll be able to start breeding for your body type and color. Mine are selected for a golden body color and long colorful tails. With your fish I immediately thought of half-black orange. I think it would be beautiful. I've greatly enjoyed the hobby over the years. I hope you will too.
-Hal

hal, my thoughts exactly! half black orange. :)

i noticed today that my male is getting a pretty blue-green coloration in his body. his tail is a more red orange than my "sunburst" female (that is what i call her)

do you feed your fry anything special other than finely crushed flake, say live brine?

i finally rec'd my tank cover so they heat can get above 72 :)
thanks for your post!