NEDOC,
work on a few angles. First if you want to do the gelatin capsule idea in a doughball then there are small quantities you can order on ebay, and the thickness of the capsule wall plays a big role in how fast it breaks down once it is wet. You can also speed up capsule dissolution by filling the 2 capsule halves, then putting them together, then using a needle to put a hole (experiment with size) on each end of the capsule. The idea would be to keep most of the active ingredient in the capsule for long enough for the doughball to be eaten, but also at the same time get some of the moisture from the environment outside of inside the fish to get on the inside of the gel capsule to help dissolve the capsule from the inside and the outside.
The other thing that may affect toxicity is whether the poison can work from the inside of the fish through GI absorption, or if the surface effect on the gill is the more rapid/deadly mechanism. There are clear effects once the stuff hits the blood on the internal organs and on the red blood cells. But there also is a direct blocking of oxygen uptake right at the gill level. This would of course require the toxin to be evenly distributed in the water of the tank. That would not be our goal for your test purposes.
The 'loaded corn' would work as a delivery tool, I'm just not sure if the loaded corn would float and other fish would target it, or if it would sink rapidly and only the carp would target it?
Also, if you have access, the other variants in the same family may have more potency at lower doses. I know there has been some study with malathion, permethrin and the newer synthetic types of pyrethroids.
We have a local irrigation supply house that supports fertilizer, lawn care and underground sprinkling companies and they sell gallons of the stuff for quite cheap.
Cold water makes the stuff work better so consider that when comparing a indoor warm water dose vs current outdoor cold temperature pond water.
