The Species 8472 bio-ship was an organic vessel that was used by Species 8472 and had a similar genetic makeup to their pilots. Each craft carried only one crew member, who acted as the vessel's pilot.
The bio-ships were very heavily armed and shielded, equipped with an extremely powerful energy beam weapon that could destroy even Borg starships easily. Although the beam appeared less coherent than either Starfleet or Borg weapons, it was able to inflict greater damage; for example, the Intrepid-class USS Voyager was knocked off course by a beam that just missed it. The bio-ships, and members of the species themselves, were resistant to assimilation by the Borg. A bio-ship's hull was resistant to other conventional weaponry too, and reflected sensor scans and tractor beams.
The bio-ships contained a series of vein-like conduits which carried electrodynamic fluid, possibly for use as an energy source. Inside a bio-ship, the walls and floor appeared to be flesh. Material similar to spider web was used in place of an EPS system. The structural supports were made of bone. The ship's computer was similar to a nervous system and used neuropeptides.
Capable of warp speed, the bio-ships were native to fluidic space and were able to function as well in the organic matter of fluidic space as they were in the vacuum of normal space. They were also equipped to detect pressure waves that were typically created when a vessel crossed into fluidic space from normal space.
Eight of these ships could collect and combine their firepower, using an energy focusing ship, which enabled them to fire a blast so powerful it could destroy a planet. When the Borg entered fluidic space, they were forced back by this resistance. Defense against these ships was found by Voyager's crew, in the form of modified Borg nanoprobes. (VOY: "Scorpion", "Scorpion, Part II", "Prey")