| I wouldn't just take them out of that tank and throw them into one that is say 78 degrees no.
Do you have another tank or bin of some sort you can warm them up a bit slower in.
Or another option is warm the tank they are in now say to 74*F over 2 days or so. This will help you in two ways, one it will warm the fry to a temp so you can put them in a warmer temp tank. And the second it may trigger a spawn from your Gymno's. Either way you would get the fry out, and if nothing happens with the Gymno's give it 3 weeks or so and then just take the heater out again. You would still be able to cool them for 2 months or so.
It is great they are eating but I just wouldn't feed them so much in that cold of water. My Gymno's too are very active when I come to feed them during the cool down, but I only do it 2-3 a week.
Or you could leave them as is. But if you do I would just look at feeding less which will slow down the growth of the fry so.... its up to you on which to do. But 60* to 78* all at once on fry probably wouldn't work out to good.
Brian | 
