  We present timing solutions for eight binary millisecond pulsars (MSPs)
discovered by searching unidentified Fermi-LAT source positions with the 327
MHz receiver of the Arecibo 305-m radio telescope. Five of the pulsars are
"spiders" with orbital periods shorter than 8.1 h. Three of these are in "black
widow" systems (with degenerate companions of 0.02-0.03 solar masses), one is
in a "redback" system (with a non-degenerate companion of $\gtrsim 0.3$ solar
masses), and one (J1908+2105) is an apparent middle-ground case between the two
observational classes. The remaining three pulsars have white dwarf companions
and longer orbital periods. With the initially derived radio timing solutions,
we detected gamma-ray pulsations from all MSPs and extended the timing
solutions using photons from the full Fermi mission, thus confirming the
identification of these MSPs with the Fermi-LAT sources. The radio emission of
the redback is eclipsed during 50% of its orbital period, which is typical for
this kind of system. Two of the black widows exhibit radio eclipses lasting for
10-20% of the orbit, while J1908+2105 eclipses for 40% of the orbit. We
investigate an apparent link between gamma-ray emission and a short orbital
period among known binary MSPs in the Galactic disk, and conclude that
selection effects cannot be ruled out as the cause. Based on this analysis we
outline how the likelihood of new MSP discoveries can be improved in ongoing
and future pulsar searches.
