Many hobbyists have had clams spawn under stress. I myself have seen it at past MACNA conferences.
The problem is raising the "baby" clams - calle veligers. They remain in the plankton for quite some time and need a lot of planktonic type foods to survive and settle. They also need to find zooxanthellae to ingest and harbor.
Most clam breeding is done in concrete raceways in tropical locations, using natural seawater.
i ve try to bred Clams in a domestic Reef tank during 1 year , and i ve stop this for a principal reason is the lake of mature clam and the price of each of them.
they don't really need plankton, but they do need zooxanthellae, that can be obtain from a scratch mantle, that must be pass in a laboratory "centrifugeuse" (en français).
To obtain a spawning you also need fermented gonad... you must kill one of them and the spawning is a big stress for the animal and some of them could dye from it.
I have been researching this subject and have had 3 successful spawns induced with serotonin injections. I was able to keep larval clams alive for 2 months. My work continues but I do believe it is possible in the near future. Adam