The drying of clay wont hurt anything, most of the clays we have here in the midwest are extremely high shrink swell clay, which means when they dry out they will shrink exponentially, hence the cracks in it, but when wet they will expand and seal up tighter then Dick's hatband, and your cracks wont go very deep and will only serve to introduce water, moisture, to the subsurface, creating your sealing expansion.
There are many experts on this site, of which I'm not one, but have worked with dirt and clay for many years as an excavator, and have built and repaired a number of ponds in this area over the years, My theory is to pump it full of water and allow the cracks to seal themselves, and put your fish in directly afterwards, Ive actually done that before, upon completion of the pond, pump some water into it and threw the baitfish in without any problems.
I'm assuming during these hot dry summer months most of the experts are probably busy working long hrs and might not get on here as much,,,, Good Luck!
