You will need to put the starfish question up in the saltwater/brackish forum to get the attention of the people who would know , it would help if you tell us which species or post a picture with it as different species have different requirements, also how long have you had it and how are you keeping it, would be good info to include.
The title fathead minnow is just related to the number of posts you have made, you start as an egg and the title changes as you get more posts, some members have asked that the title be changed, in my case to something silly.
Now on your shovelnose, we need to know which type of shovelnose it is. The maximum size and growth rates differ a lot between species.
If it is a TSN (tiger shovenose) (Pseudoplatystoma fasciatum) they can get over 40" long and grow quickly. when kept in good conditions a 2" baby can reach 10" in 4 months, 18" in 12 months, and 36" in 36 months. This picture is from a site called fishbase.
By the way, welcome to MFK.