<P> Due to the poor level of photosynthetic light reaching deep - sea environments, most fish need to rely on organic matter sinking from higher levels, or, in rare cases, hydrothermal vents for nutrients . This makes the deep - sea much poorer in productivity than shallower regions . Also, animals in the pelagic environment are sparse and food doesn't come along frequently . Because of this, organisms need adaptations that allow them to survive . Some have long feelers to help them locate prey or attract mates in the pitch black of the deep ocean . The deep - sea angler fish in particular has a long fishing - rod - like adaptation protruding from its face, on the end of which is a bioluminescent piece of skin that wriggles like a worm to lure its prey . Some must consume other fish that are the same size or larger than them and they need adaptations to help digest them efficiently . Great sharp teeth, hinged jaws, disproportionately large mouths, and expandable bodies are a few of the characteristics that deep - sea fishes have for this purpose . The gulper eel is one example of an organism that displays these characteristics . </P> <P> Fish in the different pelagic and deep water benthic zones are physically structured, and behave in ways, that differ markedly from each other . Groups of coexisting species within each zone all seem to operate in similar ways, such as the small mesopelagic vertically migrating plankton - feeders, the bathypelagic anglerfishes, and the deep water benthic rattails . "</P> <P> Ray finned species, with spiny fins, are rare among deep sea fishes, which suggests that deep sea fish are ancient and so well adapted to their environment that invasions by more modern fishes have been unsuccessful . The few ray fins that do exist are mainly in the Beryciformes and Lampriformes, which are also ancient forms . Most deep sea pelagic fishes belong to their own orders, suggesting a long evolution in deep sea environments . In contrast, deep water benthic species, are in orders that include many related shallow water fishes . </P> <Table> <Tr> <Th_colspan="2"> (show) Species by pelagic zone </Th> </Tr> <Tr> <Td_colspan="2"> Many species move daily between zones in vertical migrations . In this table they are listed in the middle or deeper zone where they are regularly found . </Td> </Tr> <Tr> <Th> Zone </Th> <Th> Species and species groups include...</Th> </Tr> <Tr> <Td> Epipelagic </Td> <Td> <Ul> <Li> mackerel, requiem and whale sharks </Li> <Li> clupeiforms - herring, anchovy </Li> <Li> Salmonidae - salmon </Li> <Li> atheriniforms - flyingfishes, halfbeaks, sauries </Li> <Li> perciforms - jacks, dolphinfish, pomfrets, barracudas, tunas, billfish . </Li> </Ul> </Td> </Tr> <Tr> <Td> Mesopelagic </Td> <Td> Lanternfish, opah, longnose lancetfish, barreleye, ridgehead, sabretooth, stoplight loosejaw, marine hatchetfish </Td> </Tr> <Tr> <Td> Bathypelagic </Td> <Td> Principally bristlemouth and anglerfish . Also fangtooth, viperfish, black swallower, telescopefish, hammerjaw, daggertooth, barracudina, black scabbardfish, bobtail snipe eel, unicorn crestfish, pelican eel, flabby whalefish . </Td> </Tr> <Tr> <Td> Benthopelagic </Td> <Td> Rattail and brotula are particularly abundant . </Td> </Tr> <Tr> <Td> Benthic </Td> <Td> Flatfish, hagfish, eelpout, greeneye eel, stingray, lumpfish, and batfish </Td> </Tr> </Table>

Which of the following is not a common adaptation of deep-ocean fishes