Can someone help me with the species identification of silver dollars

[Bbg81018]

I have had these silver dollars for over a year now and have a few questions on their species. I have had the silver dollar in the first photo for less time but he has a much smaller hook and dorsal fin and a much longer adipose fin while the second silver dollar has a more defined hook and long dorsal fin with a small apidose fin. The silver dollar in the second photo was bought at a larger size but the newer ones are larger than the irginal size of the second silver dollars and still have a less developed hook. They also have a red tint at the end of their tails which is not present on the second photo silver dollar. The last difference is that the silver dollars in the first photo have a black bar on their eyes while the second silver dollar just has the black of his pupil. Im just wondering why all of these differences are present.

 

[kno4te]

First pic is metynnis hypsauchen. Second pic looks like myloplus rubripinnis.

 

[MatteoTheEnder22]

The second pic definitely looks like a red hook but the first one no clue.

 

[L3CTR0N]

First pic is metynnis hypsauchen. Second pic looks like myloplus rubripinnis.

This definitely.

 

[FJB]

I agree with a Metynnis for the first, certainly a female. The single image does not allow a species level id, with any certainty but due to the lack of any spotting, M. hypsauchen sounds like a good guess, but there are are least three other very similar species.

The second fish is certainly a male red hook, Mylopus rubripinnis.

Nice fish!