Q: Hi Faith, thank you for taking the time to build this very informative site.  I just found my fry (5 weeks) catching and devouring one of its siblings.  I like to avoid jarring them all because of the large number of containers needed, is there another better way to separate them and prevent this from happening again.  Thank you

Question submitted by Brian, Honolulu - Hawaii

A: Hey Brian, maybe you should feed your fry every now and then LOL.... But seriously, it is highly unusual for 5 weeks old fry to eat each other. Usually cannibalism will happen when some fry become severely larger than others (2 to 2 times the size). At which point the larger fry may snack on their little brothers/sisters (yikes!). 

There should be no reasons for you to have to jar all your 5 week old fry. Although you did not mention a size difference, I am going to guess and say that the betta who ended up a snack was much much smaller. Otherwise how could it have been "caught"? "Catching" as you said implies (to me) that the predator was able to bite and hold its prey with its jaws, signifying a large size discrepancy. 

To avoid having larger fry snack on the runts, you can do two things:

bullet isolate the runts: Coral the runts in a "fry coral" as I call them. These are easy to find at your local fish store and are made of fine mesh covering a plastic square structure.
You can hang such a device inside the tank, the fine mesh walls allow water to flow through, keeping it healthy for the runts. Net your runts and place them inside. They will no longer be accessible to the rest of the fish so they can't get eaten. Also they will not have to compete with larger fish for food so they will grow faster and are not likely to die. remember however to place food inside the coral for them to eat!
bulletjar the bullies: If a few of your fry have grown way larger than the rest, you might want to jar just those. Give everyone else in the tank a break from their tyranny. 

Hope this helped you :).