Rattails of the family Macrouridae lack a distinct caudal fin. The trunk narrows steadily from a large head into a long filament, and the second dorsal and anal fins extend almost to the tip. Propulsion comes from undulating this tapering rear section, which suits slow, sustained cruising just above the sea floor rather than bursts of speed.
The head is where the sensory investment sits. Grenadiers have large olfactory organs, and baited camera work in the deep sea consistently shows them arriving at falls of carrion, tracking odour plumes upcurrent. Giant grenadiers also take squid, fish and benthic invertebrates.
Grenadiers matter out of proportion to their public profile. They are among the dominant fishes by biomass on continental slopes, they are long-lived and slow-growing, and they are taken as bycatch in deep trawl fisheries, which makes their populations sensitive in ways that are hard to detect without dedicated deep surveys.