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  • Specimen of the Week 328: Sawfish Rostrum

    By Nadine Gabriel, on 2 February 2018

    This week’s Specimen of the Week is a guest edition by Front of House Volunteer and UCL Student of History and Philosophy of Science, Leah Christian. Read on as she reveals that her Specimen of the Week is…

    ** Sawfish (Pristis sp.) rostrum**

    Rostrum of Pristis sp., LDUCZ-V1536

    Amongst the sharks and rays in Case 15 is the engaging sawfish snout. No points for guessing how this ray got its name; the evenly spaced teeth along its rostrum tell the whole story.

    What is a sawfish?

    “Sawfish” is a broad term for members of the Pristis genus and is a class of cartilaginous fish that also includes sharks, skates, and rays. Five species are known – Narrow, Dwarf, Smalltooth, Largetooth, and Green – all of which are endangered as a result of habitat loss, illegal fishing, and entanglement in fishing nets.

    Sawfish may be found in tropical and sub-tropical parts of the world, ranging from the coastal shallows to depths of 100 m. The Largetooth sawfish (Pristis pristis) is particularly adaptable, having been found not only in oceans but also in the freshwater Lake Nicaragua, Nicaragua. They tend to stay close to the seafloor, feeding primarily on fish and molluscs found there.

    A Largetooth sawfish. Image by David Illif via Wikimedia Commons, CC BY-SA 3.0

     

    Why the long face?

    Originally, biologists believed that the sawfish used its distinctive rostrum to dig in mud and sand for its prey. However, its real use is far more interesting. The sawfish engages its prey in the open water, striking sideways with its saw and impaling the unfortunate fish on its teeth. If the sawfish encounters its prey near the bottom, it may pin the fish down in order to manipulate it into a better position for swallowing. But that’s not all. Lining the rostrum are tiny pores called ampullae of Lorenzini, which are often found in sharks and rays. These pores are electroreceptors, meaning they detect weak electric fields (such as the weak electric fields generated by living beings). This ability allows the sawfish to hunt even in dark water.

    What’s the best party fact about the sawfish?

    In 2015, ecologists conducting a genetic study of a Florida, USA, population of the smalltooth sawfish (Pristis pectinata) found seven individuals with DNA from only one parent, indicating that female sawfish reproduced without the involvement of a male sawfish. This asexual reproduction in a normally sexually reproducing species, called parthogenesis, has been observed in some captive animals such as snakes and sharks, but healthy offspring conceived this way had not been observed in the wild. This unusual discovery caused something of a stir among sawfish enthusiasts, and raised the question of “why?” The study authors suggest it is a response to the low population, although it’s too soon to tell if these offspring will be able to successfully have offspring of their own.

    References

    http://www.bbc.co.uk/news/science-environment-32958033
    http://sawfishconservationsociety.org/Rostrum%20use.htm
    http://sawfishconservationsociety.org/microdon.htm
    http://www.iucnssg.org/conservation-strategies-sawfish.html

    Leah Christian is a Front of House Volunteer in the Grant Museum of Zoology, and a UCL student of History and Philosophy of Science.

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