The fish featured in the video below is a largetooth sawfish (Pristis pristis) filmed at the National Aquarium in Baltimore. Its most distinctive feature is the elongated snout covered with teeth called a rostrum. Sawfish have a shark-like tail and dorsal fins, and they even swim like sharks and share a common ancestor with them. However, sawfish are not sharks, they are a type of ray called a batoid. One difference between sawfish and sharks is that sawfish have the gills under their bodies (ventral gills) while the shark’s gills are on the sides of their bodies (lateral gills: see the next video). As you can see in this video, the sawfish can funnel water into their gills through holes called spiracles situated behind their eyes, whereas the shark relies on water moving through their mouth and into their gills while they swim (although some species can pump it using their pharynx while lying still).
Sawfish are an ancient group of fishes going back over 56 million years. They can grow to 23 feet in length and weigh 2000 pounds. They mostly feed on crabs, shrimps, and other fishes. Sadly, these magnificent fish are endangered due to habitat destruction and over fishing.
Featured in the next video is a sand tiger shark (Carcharias taurus) also filmed at the National Aquarium in Baltimore. Sand tiger sharks have two interesting characteristics. The first is that they exhibit what is called “embryophagy". This means that during gestation, the largest embryo in the uterus will attack and eat the others! The second interesting characteristic has to do with buoyancy. The body of sharks is denser than water, but because sharks have no swim bladder, in order to avoid sinking, sharks have to swim continuously. However, the sand tiger shark can take in air from the surface and hold it in its stomach thus adjusting its buoyancy.