why would one senegal's face be half as wide as another?

[Aquarium_Fish]

why would one Senegal have a narrower head than another?

I have an ornate who has a broader head than my smaller Senegal (which is about the same length as it).

the ornate head is about as broad as the larger Senegal ...

I was wondering if that would be a species characteristic (like other than a Senegal) or a male/female thing?

 

[elbeatch]

Well ornates tend to have wide heads to begin with, so comparing the ornate with the sen might not be fair to the poor sen. With it being a sex thing, females tend to look like they have smaller heads but it's usually because their bodies are stockier. As far I I know though, the anatomy for head diesn't change from one sex to another. If you're looking to sex your bichirs check the size of his/her anal fin, unless they're too yound, you'll find the male has a thicker fin there.