Stem with seeds?

[plantmania]

I've observed some floating stems... after lights off. it's very soft and jelly like (breaks easily) and embedded within them are little black seeds. or eggs

Know which aquatic plants or fishes that releases them ?

[plantmania]

Found out the plant is my Blyxa japonica .... It's been releasing "stems" with seeds which floats for a while and then disintegrate/"melt" to release the seeds...