Those sticks/stones/whatever would be wet anyways, so no sparks, let alone flames, would arise from this.
Moreover, say a fire was made. Then what? Will the fish just hold it above the water indefinitely? Building a floating platform smithy that would stay afloat with all the heavy stones AND fuel necessary to stoke a fire long enough to smelt metal would be inconveniently large, and not something a species trying to survive would waste a tonne of resources building with no obvious logical recompense.