death by over feeding

Recently I moved my SRBD fry to a 55 gal "growout" tank.
After the move it became apparent that the fry were not growing at a uniform rate. They seem to segregate in the tank according to size, with the smallest staying at the bottom in a back corner. Possibly because there is less current from the two HOB filters.
It's much harder now to distribute the food so that all get enough but none get too much.
Yesterday I was feeding baby brine shrimp and got carried away trying to get enough down to the runts in the back corner. About an hour later I saw that several of the biggest [obviously most aggressive feeders] were tumbling helplessly in the current in obvious distress with huge distended bellies. Some eventually seemed to recover. By this morning 3 or 4 were still alive but obviously on their last leg. One, the biggest of all, and my favorite, was dead.
I took it to work a dissected it under the low power microscope. The abdomen had actually split open from the vent to about halfway toward the head. It was not the stomach that split however. Although totally distended, the stomach was intact. What seemed the cause of the split was a foamy, bubbly substance that had the consistency of fat gobules. In other words, the little clear bubbles did not break easily like plain foamy water, but were presistent and slippery and difficult to puncture with tweezers. As best as I could determine with the higher power microscope, the stomach content was all brine shrimp and no egg casings as I had feared.
Anyone want to venture a guess what happened?
Anyone have a suggestion on how to safely feed all the fry without seperating them?

How large were the fry?

They are all ~ 0.5 inch. Some bigger, some smaller. Actually the size difference is really more with bulk than length. Some are shaped like adults with nice full, proportional bodies while others are still in fry shape, long and thin but with bellies that stick out after eating.
When they first swam up I tried to provide lots of tiny critters but I fell into the habit of using ground up flake for its convinience and because they ate it really well. Some seemed to do Ok on it but apparently there are lots of others that were not thriving. Now I've got them in a bigger tank and I'm feeding baby brine and I'm starting to lose some. Besides the over eating problem, I'm seeing some that are wasting away. I'm finding deads that are just skinny slivers that didn't seem to grow much at all.
I'm gonna have to try again. My adults are still totally colored up and fat. They seem to be spawning in the main tank along with black nose dace which have been spawning in there. Too many darters and hungry minnows for any eggs or fry in there.
Time to reassemble the chub nest!

Have you dissected any healthy fry to see if this substance is present?

The best way to distribute live foods to specific fishes is to use a large 60cc wide bore syringe or, more commonly, a turkey baster. Distract the larger fishes with food and use the turkey baster to get some food to the smaller guys, you will likely still overfeed the larger guys a bit, but hopefully not to the point where you get the problems you were having.

You can also try creating a "floating basket"; with larger fish I usually use a laundry basket with "noodles" (the foam pool toys) cut up and fixed near the lip to keep it afloat. With smaller fishes you can get a small plastic shoebox size (or smaller) container from the housewares section of the local mega-mart, cut large holes in the sides, add window screen (plastic, not the metal stuff) to cover the holes, secured all the way round the edges with hot-glue or silicone sealant, and then add floats.

Usually if you can keep smaller fishes isolated long enough and give them ample food, they will catch up with their tankmates and you can put them back in with the general population. With some small fishes I've even added all the food into the floating baskets, letting the smaller guys go to town for a few minutes while the food escapes out to the general tank.
Hope this helps,
-Barrett

The best way to distribute live foods to specific fishes is to use a large 60cc wide bore syringe or, more commonly, a turkey baster. Distract the larger fishes with food and use the turkey baster to get some food to the smaller guys, you will likely still overfeed the larger guys a bit, but hopefully not to the point where you get the problems you were having.

You can also try creating a "floating basket"; with larger fish I usually use a laundry basket with "noodles" (the foam pool toys) cut up and fixed near the lip to keep it afloat. With smaller fishes you can get a small plastic shoebox size (or smaller) container from the housewares section of the local mega-mart, cut large holes in the sides, add window screen (plastic, not the metal stuff) to cover the holes, secured all the way round the edges with hot-glue or silicone sealant, and then add floats.

Usually if you can keep smaller fishes isolated long enough and give them ample food, they will catch up with their tankmates and you can put them back in with the general population. With some small fishes I've even added all the food into the floating baskets, letting the smaller guys go to town for a few minutes while the food escapes out to the general tank.
Hope this helps,
-Barrett

Thanks!
I guess great minds think alike.
I actually had already settled on a large bore syringe that happened to have a nipple the perfect size for air line tubing. I attached the tubing to a weight, dropped in to the back corner where the runts hang out then very gently squirted little bits of baby brine right into the cluster of smaller fry. I also found a little dash of powdered flake sprinkled on the surface distracted the aggressive feeders long enough to get plenty of food to the more needy. This is the way I have been feeding my darters in the big community tank full of hungry dace and minnows.
I also found out the hard way it's better to make multiple small feedings than a few bigger ones. I'm not gonna sweat losing a few of the runts. They are apparently less robust, poor feeders. There's no point going to heroic measures to save the inferior offspring at the expense of the more robust, more desirable fry.
Now that I lost a few of the biggest and several of the smallest, the gap is closing and what's left is more uniform in size.

And no, IM, I wasn't sufficiently curious to sacrifice a healthy specimen to look inside. For want of a better explanation [I was hoping for more insight from our scientifical forum mates ], I'm going with the theory that the foamy air in the abdomen was caused by the distended stomach squeezing on the swim bladder. This is consistent with the difficulty in swimming I observed. There was no gas in the stomach itself, it was just tightly packed with brine shrimp.

More so out of curiousity but do you have shots of the fry, especially side by side shots of the more larval looking ones with the proportional ones.

More so out of curiousity but do you have shots of the fry, especially side by side shots of the more larval looking ones with the proportional ones.

I don't. There aren't many, if any left that looked more like the larvae. They've either died off or had growth spurt after I started brine shrimp.