Friday, December 18, 2015

Atlantic Needlefish by Don Orth

Who am I?  I have a really long body with my upper and lower jaws studded with numerous sharp teeth.  I specialize in appearing invisible near the water surface.  I often leap and skitter across the water surface at high speeds when alarmed.  I impale humans even though I am not a swordfish or billfish.  I can attack fish prey by diving down from the air.  I have a single, not paired, gonad. I have green bones.   Who am I?    If you guessed “needlefish,” then you are correct!

Atlantic Needlefish Strongylura marina (Walbaum) Photo by Michael Clark ©
Needlefishes comprise a New World clade of fishes distributed along the Pacific and Atlantic coasts of the Americas and in freshwater basins of Central and South America. Of the ten genera, three are endemic to South American rivers.  The clade is most closely related to the flyingfishes (Excocoetidae) and Halfbeaks (Hemiramphidae).    Our most common North American species is the Atlantic Needlefish Strongylura marina (Walbaum).  Strongylura is from Greek strongylos, meaning round and oura meaning tail, which refers to the round cross section shape.  The species name marina is from the Latin marinus, meaning “of the sea.” Atlantic Needlefish is long, slender, and typically a silvery color with a dark blue stripe along the side of its body.  They grow to about 2 feet and the upper and lower jaws extend into long beaks filled with sharp teeth.  They are native to the western Atlantic from Massachusetts to Brazil, including coasts of the Gulf of Mexico and the western Caribbean Sea.  Atlantic Needlefish are most commonly found in estuarine and shallow coastal habitats but can sometimes move to freshwater areas such as coastal ponds or rivers.  Spawning occurs in freshwaters where the adults often migrate in search of juvenile fish prey.

The Atlantic Needlefish is a frequent invader of rivers up the Fall Line.  It maintains freshwater populations in some river systems.  It is physiologically well adapted to salinity fluctuations.  In fact, after the construction of the Tennessee-Tombigbee Waterway in 1985, the Atlantic Needlefish gained access to the Tennessee River drainage in Alabama and Tennessee where it maintains freshwater populations.

The long nose and hundreds of tiny, sharp teeth of the adults mean that this is a serious predator on other fishes.   Needlefish swim near the surface and feed on small fishes by charging the prey and clamping it between its jaws.  The jaws are then manipulated to orient the fish head first so it may be easily swallowed.   The juveniles have longer lower jaws than upper jaws and feed on amphipods, shrimp, and mysids.    The jaw morphology is reflective of the diet.    

Just look at those teeth!  Photo by James Green
Atlantic Needlefish are fast swimmers and have a unique form of locomotion, referred to as anguilliform.  Anguilliform refers to the large undulations of a long body that are also seen in eels.  However, other anguilliform fish tend to move through complex habitats, not open or near surface waters.   The needlefish is different in that the origin of the pectoral fin base is high on the body and the bases of their relatively large pectoral fins are oriented closer to vertical than to horizontal.  Pectoral fins of the needlefishes serve as stabilizers during fast swimming.
Anguilliform swimming of Atlantic Needlefish at 1 L/sec Photo: Liao 2002.
Adult needlefish also have another way to stalk and attack schools of prey fishes.   The adult needlefish actually leaps out of the water and makes an aerial attack on unsuspecting prey fish.  This strategy greatly increases their attack range.   And with their toothy gape, the success rate is very high.
Aerial attach in needlefish.  Day et al.  2015
Atlantic Needlefish is not immune to predators. Large fish and fish-eating birds, such as the Osprey and the Black Skimmer, prey heavily on Atlantic Needlefish.  One manner of hunting and escaping from larger predators is to leap and skip across the surface of the water when alarmed.  Its defense against predation involves rapid lunging at predators, sometimes penetrating them with the needle-like nose. Since the Atlantic Needlefish is so common it often the basis for designing lures and flies for sportfishing.
Needlefish lure from (left) and needlefish fly from (right)
The shallow, coastal waters attract numerous aerial and aquatic predators.  Fast swimming, jumping, and skittering across the surface are all effective anti-predator strategies.  Yet, the needlefish has one other adaptation to reduce predation.   Predators cannot strike if they cannot see their prey.  The needlefish specializes in appearing invisible in the clear, well-lit surface waters.   Other fishes can do this as well.  These “invisible” fish have platelets in their scales that reflect polarized light (i.e, light moving in a single plane) in such a way as to blend in.  Recently, investigators used a camera system that showed that these invisibility-specialist fishes hid well in polarized light.  Since polarized light is common underwater, the invisibility specialization is used by many fishes.  The needlefish is just one of many fish that take advantage of this.

Atlantic Needlefish blends in with its surroundings in this coral reef habitat.  Photo: D.J. Orth
Atlantic Needlefish represent a great example of the phenomenon called “heterochrony.”  Heterochrony is defined as developmental change in the timing or rate of events, leading to changes in size and shape.  In the Atlantic Needlefish, the jaw changes with maturity, as upper jaw grows more slowly than the lower jaw.   At hatching (~9-14 mm), larvae are “halfbeak” in appearance and both jaws are short and of equal length.  Small juveniles (35-50 mm) continue to resemble a halfbeak, where the upper jaw is much shorter than the lower jaw.   At full maturity, both jaws are approximately equal in length.    The jaw morphology reflects a diet of plankton during the “halfbeak” stage and a fish diet during the adult stage.
Atlantic Needlefish at halfbeak stage and needlefish stage (Boughton et al. 1991)

How did this heterochrony ever happen?   The ancestral member of this group was presumably similar to the halfbeak.  Then genetic mutation to permit equal growth of upper and lower jaws.
Hypothesized evolutionary tranistion from the halfbeak-type ancester to the needlefish (Lovejoy and Collette 2001)
Needlefish are fun to catch on light tackle (see video and video).  Since they are active feeders you can catch them with small fish or shrimp as bait.   Needlefish are attracted to light so you can also draw them in with a flashlight if fishing at night.   A hard strike is needed to hook the needlefish.  Expect it to jump in the air while you reel it in.  Be careful to keep your fingers away from those sharp teeth!  The International Game Fish Association’s hook-and-line record is 1.47 kg (=3 ¼ pounds).    Many anglers practice catch and release, but needlefish are edible. You are in for a big surprise when you clean a needlefish.  The bones appear green due to a heme degradation product, biliverdin, which has an affinity for the structural protein associated with the bone. Also, when you examine the entrails you will not find paired gonads that are characteristic of fish.  The needlefish has only one gonad, an adaptation seen in other long-bodied animals.
The bones of needlefish are green!  Photo by
One of the unfortunate human interactions with needlefish occurs due to their behavior of jumping and skittering across the water surface.  Human injuries are thought to be accidental when the needlefish is startled; although some reports sensationalize the encounter and report that “needlefish attack at 60 km per hr.”  Needlefish are attracted to bright lights and injuries are often reported among night fishermen who get between lights and lunging needlefish.  Injuries have also been reported in swimmers, canoe, divers, riders, surfers, and windsurfers.  In fact Richard Clinchy’s Dive First Responder (1996) includes a section on Needlefish Punctures.   Windsurfing creates a greater risk to speed of needlefish and windsurfers, which may achieve a relative velocity of perhaps 100 km/h or more.  Although injuries are rare, they can be life threatening depending on the organ injured.    Risk of impalement by a fish is greater for needlefish than for those truly weaponized fish, such as the swordfish and marlin.  
Radiograph of lower limb impaled by needfish.  photo by Link et al. 1999.
My advice is “Save the Needlefish” and avoid windsurfing. The needlefish dies and the windsurfer ends up in the local emergency room.  Also, avoid using gill nets in areas with schools of needlefish.   Needlefish have to be among the top fish you don’t wish to encounter in a gill net. 
Needlefish entanged in a gill net.
Boughton, D. A., B. B. Collette, and A. R. McCune. 1991. Heterochrony in jaw morphology of needlefishes (Teleostei: Belonidae). Systematic Biology40(3), 329
Brady, P.C., and sixteen coauthors.  2015.  Open-ocean fish reveal an omnidirectional solution to camouflage in polarized environments.  Science 350(6263):965-969.  DOI: 10.1126/science.aad5284      
Clark, J.J., H. C. Ho. 2012.  Two cases of penetrating abdominal injury from needlefish impalement.  Journal of Emergency Medicine 43(3):428-430. doi:10.1016/j.jemermed.2009.10.013
Day, R.D., F. Mueller, L. Carseldine, N. Meyers-Cherry, and I.R.Tibbetts.  2015.  Ballistic Beloniformes attacking through Snell’s window.  Journal of Fish Biology   DOI: 10.1111/jfb.12799
J├╝ttner, F., M. Stiesch, and W. Ternes. 2013.  Biliverdin: the blue-green pigment in the bones of the garfish (Belonebelone) and eelpout (Zoarcesviviparus).  European Food Research and Technology 236:943-953. 
Liao, J.C. 2002.  Swimming in needlefish (Belonidae): anguilliform locomotion with fins.  The Journal of Experimental Biology 205:2875-2884.  
Link KW, Counselman FL, Steele J, et al. 1999. A new hazard for windsurfers: needlefish impalement. Journal of Emergency Medicine 17:255–9.
Lovejoy, N.R., and B.B. Collette. 2001.  Phylogenetic relationships of New World Needlefishes (Teleostei: Belonidae) and the biogeography of transitions between marine and freshwater habitats.  Copeia 2001:324-338.
Rouvillain, J.L., A. Donica, C. Gane, C. Zekhnini, E. Garron, and A.P. Uzel.  2013.  Windsurfing hazard caused by needlefish.  European Journal of Orthopaedic Surgery & Traumatology  23(2):293-295.  

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