Dumb questions about DR. Ude Romer's book

[Hanzo]

I know this will tag me for the newbie that I am, but here goes. I just got the cichlid atlas, and enjoy reading true it. But in the end of each species, there information about lenght, temperature and so on. But there also something but down like this -> R: b,m D:2-4

What on earth does this mean?

 

[Hanzo]

Nobody knows? I really have been looking all of the book for this input, but so fare no luck.... This numbes are togheter with the temperatur, lenght of the fish and minimum tank size. Somebody?

 

[farm41]

R: b,m D:2-4

What on earth does this mean?

R = region the fish lives in the water column, bottom to middle in this case

D = degree of difficulty to keep, 1 being easiest, 4 being hardest.