As per the FAO FIShing -------site
Spawning temperature is generally between 18 ºC and 30 ºC, with an optimum of 22-28 ºC. The eggs of silver carp, like all Chinese carps, are non-adhesive. After spawning, the eggs begin to absorb water through the egg membrane and swell until its specific gravity is slightly greater than that of water, so they can stay at the bottom (in the case of static waters) or float halfway in mid-water (in flowing waters) until the fry hatch. So with even warmer temps at shorelines, inlet rivers & harbors they will do some spawning.