Hello. D imitator tend to be around 20mm when full grown (or so I'm told) and the vents (which I have experience with) are generally about the same like 18-22mm long. I don't find the vents harder to care for than any other dart; however, there is always the fear of them escaping. They can hide in just about any crevice and even underwater. Their food demands are less also.
Enjoy,
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Justin
stk18119@loki.stockton.edu
D.auratus (Costa Rican, Nicaraguan)
D.leucomelas
D.tinctorius (lorenzo, yellowback, citro, pb, oyopock,etc.)
D.azureus
D.ventrimaculatus (yellow/gold)
D.pumilio (blue jeans, solid red)
P.aurotaenia (narrow bands/green)
P.bicolor
E.tricolor (Santa Isabel)
H. leucophyllata
P. hypochondrialis azurea
P. resinifictrix
A. caladryas
etc.......