If by red hooks, it is meant Myloplus rubripinnis (not a Metynnis species), then NO : The females have the larger and straighter red hook-shaped anal fin. The males will have a bi-lobed anal fin (not straight), and the fin will be much less colorful.
On the other hand, the term "red hook" is used very loosely and with frequency applied incorrectly to Metynnis fish, which do not have a "hook". Thus, it is only worth talking about it upon seeing pictures of the fish. Otherwise nobody knows what kind of silver dollar is meant. That's why the pictures you showed were so useful, and I suggested they are M. altidorsalis, 1st picture a female, 2nd picture a male. It would become necessary to see pictures of your red hooks.
On the other hand (I know that is 3 hands!), not all Metynnis are the same in terms of gender differences: In M. fasciatus (tiger, or stripped sd's), and in M. hypsauchen, both males and females will have a small "hook" in the anal fin of full-grown fish (much smaller than in "real" red-hooks, M. rubripinnis). But the males will have a bilobed (but ending in hook) anal fin.
A bit confusing, I agree!!
I reckon I’ve got a 50% chance of getting it right ?
