i changed my substrate fom gravel to sand about a month ago , bin with gravel has been out side with a bit of water still in and rain water , was going to empty it out and there is fish fry in there !  very small fry but definetly fry , could be ctenopoma ,uaru,or chocolate cichlids i dont know ,i have bought some indoors and placed in a breeding net  
 
watch this space  8)