If you watch them carefully they eat anything they can. The sack around a wiggler is filled with nutrients, (the rock they were laid on grew an immediate carpet of algae, for example, -the fry graze on)
If they are hungry they will eat there, sure.. their tails, and bodies,, if they are big & fast enough. I try to keep them well fed but it a tiny tank.
The fry are desperate to get big, it's as if their genes know that 99% of them will not survive into adulthood.
In an ideal situation jags spawn the same in a tank as in a lake; about every 30 days. They protect the fry religiously until the new eggs are laid, at which point the older generation become the enemies of the forthcoming one and must be killed if caught. Makes perfect sense. In a lake they would swim off. In a tank they become the captive victims of their massive parents.
