Sawfish or Sawshark?
Updated: Apr 27
The term Elasmobranch is used to describe all species of shark, skates and rays because, believe it or not, sharks are very closely related to "batoids" (stingrays and manta rays), moreso than they are to fish that have a similar body shape to them, like tuna or cobia. In fact, there are some sharks and batoids that are so remarkably similar that it can be difficult to tell them apart, the sawshark and sawfish, for instance. So if you see one of these animals (you can see them aquariums sometimes), how can you tell which one is which?
Sawsharks are truly sharks, so are assigned to the group Squalimorphii and further divided into their own order called Pristiophoriformes. However, sawfish are within the superorder Batoidea and further classified into the order Pristoidei. That was a lot of crazy taxonomic words that I don't expect you to understand, but what it basically means is these guys are related, but actually not super closely related to compared to other species; sawfish are actually more closely related to rays, than to sawsharks.
That might surprise you, given the fact that both of these fish have that impressive "rostrum" projecting from the front of their faces. These might look quite similar, but in fact they are very different from each other. The rostrum of the sawfish has "rostral teeth" of all roughly equal size projecting from the side. Whereas, sawshark rostral teeth have smaller and larger sizes alternating down the length of the rostrum (Compagno, 1984).
Sawfish can also be easily told apart from sawsharks by looking at the location of the gills. Sawsharks have gills on the side of the body, like other sharks. However, on the sawfish the gills are located on the underside of the body, like their ray relatives (Compagno, 1984). So if you see a saw-like fish resting on the substrate in an aquarium, if the gills are visible, it is a shark.
Sawsharks also have sensory "barbels" which hang down from their face, where sawfish do not. These are used to detect prey hidden beneath the sand on the ocean floor. The rostrum can then be used to dig the victim up and slash it into pieces for easier eating (Compagno, 1984).
Sawfish and sawsharks also have very different habitats; you would never find them in the same place. Sawsharks live in relatively deep, offshore regions, where sawfish live in coastal areas, in relatively shallow water (Compagno, 1984).
If you did have a sawshark and a sawfish side-to-side, there are several other differences that you would be able to find. For instance, sawsharks are relatively small and slender, only reaching around 1.4 m total length (TL), but sawfish can be noticeably larger. One species, the green sawfish (Pristis zijsron) are amongst the largest fish in the world, reaching at least 6 m TL.
If you were able to look inside these two animals, you would also see many differences. Most notably, the differences in the jaws and teeth. Sawsharks have a mouth full of small, spiked teeth, whereas, the teeth of the sawfish are flattened. This is due to their differing diets; sawsharks targeting primarily small fish and squid (so their pointed teeth and handy for grasping wriggling prey), whereas sawfish favour crustaceans and molluscs (so they can use their flat teeth to grind down the hard shells of their prey) (Compagno, 1984).
These fish also differ in how threatened they are by human activity. Of the 5 known species of sawfish, 2 are considered 'endangered' and 3 'critically endangered', whilst no species of sawshark which has been assessed has yet been assigned to any IUCN category (IUCN, 2020). This is because the rostrum of the sawfish was prised as a trophy in the past, so they have all been pushed to the edge of extinction... That means a feature which made them perfectly adapted to their habitat might end up being what makes them go extinct at the hands of humans (let that sink in!). Thankfully, sawfish often do well in aquariums, so hopefully, in the future, breeding programs will manage to successfully bolster their populations in the wild.
If you interested, this video is an investment in time (at 1hour long), but very informative!
Aschliman NC, Nishida M, Miya M, Inoue JG, Rosanad KM & Naylor GJP (2012). Body plan convergence in the evolution of skates and rays (Chondrichthyes: Batoidea). Molecular Phylogenetics and Evolution, 63:1, 28-42.
Compagno LJV (1984). Sharks of the world. An annotated and illustrated catalogue of shark species known to date. FAO Fisheries Synopsis, Volume 4, Part 1 Hexanchiformes to Lamniformes, pp.130-131. Access online.
Jorgensen S (2013). Sharks: Ancient Predators in a Modern Sea. Firefly Books, Ontario, Canada. ISBN: 0228100801.