I drew this upon special request from RedAlertRiker from a star trek fan forum I partake in.
I accepted because in the Star Trek world the Borg never assimilated any intelligent lifeforms from fluid filled planets. It created an interesting challenge.
The Borg would have if their technology was advanced enough to be worth taking. I'm sure attempts were made early in the Borg evolution history. Their efforts proved somewhat disastrous by our standards. To capture these people the Borg had to fly scout ships(spheres) deep into the watery planet. Stunning them, trying to tractor them onto the ship so they can inject them with nanites. The intense pressure crushed over a dozen spheres. As the shielding technology improved they would try and try again.
"We will succeed."
So they have. The Borg understood that these creatures (adapted to water) are no good on the dry decks of ships. Their body shape is unnecessary in the vacuum of space. Considering the initial difficulty of assimilating the people and the planet... they decided best keep these creatures and use them for what they were perfected for, the assimilation of other fluidic civilizations.
Problem: Packing their bodies full of hard dense technology slowed their movement... ruins their aerodynamic design..
Solution: Give them their own propulsion system. So that's what I did... I'm not sure about warp technology but maybe an impulse drive... it may sting when activated... but I'll let others continue this tale.