I don't understand what you mean by "hints on determining finnage".
The difference between males and females in general;
Male; body slightly longer.
Usually colors are more vibrant (not always).
Bigger/longer fins (ventral longer, dorsal and caudal wider - (not long as in all DT)).
Female; the opposite to a male
body slightly shorter (looks shorter because of the fatter/wider body)
smaller/shorter fins with a less vibrant color
Has an ovipositer
These aspects apply to all tail types.
DT's caudal has two lobes... lol. The geno's has one lobe but a long dorsal - the male's is wider than the female..... same as above.
...... by DT, do you mean long finned DT?