New to this forum, but let me put my 2 cents in. Have been placing gravel to enhance spawning for warmwater fish, mostly Bream/Bass for 25 years and this is what I have observed: A. Bream prefer gravel as a spawning substrate. Why gravel?? Gravel allows for water to circulate throughout the egg mass as the guardian male fans the nest. This in turn carries the oxygen necessary for the survival of the individual eggs. Better circulation = better hatch from each nest = better fisheries dynamics. Washed pea gravel is probably best, but also the most expensive. Washed river rock #57 grade is also good and less costly. Washed rounded rock allows for better circulation. Sand, "white" rock, lime rock all tend to "lock up" and restrict the circulation of water/oxygen to the bottom of the egg mass necessary for egg survival in that part of the egg mass.
B. Thickness of the layer of spawning gravel will thin or "pancake" out after several years and eventually becomes useless. The mechanical action of fanning the beds makes the gravel migrate out over time. Counter this by boxing in the gravel with 1x12 inch cypress boards, filling in the outside of the boards with dirt. Looks like a shaved off pitcher's mound with gravel recessed in the ground. Dirt shoulders keep the hooks from snagging as easily.
C. Avoid sloping ground, level sites have the greatest use.
D. Dispurse the sites according to depth and aspect to allow for greater overall use throughout the spawning season.
E. Avoid locating sites adjacent to incoming streams, or tribs, they end up being silted in.
Just my 2 cents, hope this helps.FS.
