Wednesday, February 28, 2018

Crevalle Jack: Fish, Fishing, and Robotics, by Don Orth

The Crevalle Jack Caranx hippos is a prized game fish especially in the Gulf of Mexico.  The scientific genus name, Caranx is derived from the French word, carangue, for a Caribbean fish, and hippos is Greek for “horse” There are six species of Caranx with a cosmopolitan distribution in tropical and subtropical waters of the Atlantic Ocean and some extend to temperate zones.  All 150 species of Carangidae have hard scutes that run forward of a sickle-shaped tail. Crevalle Jacks are countershaded with greenish-bluish to black on dorsum and silvery to golden on ventral surface.  A small black spot on opercular margin and a black blotch on lower pectoral fin rays.  Young jacks provide food for numerous carnivorous fishes while the adults are carnivores.  
From Biodiversity Heritage Library, Marcus Elieser Bloch Oeconomische Naturgeschichte der Fische Deutschlands
The Crevalle Jack was described by Linnaeus in 1766 as Scomber hippos from a dried specimen. However, in 1801, Bernard Germain de Lacépède  reassigned it to the genus Caranx and the taxonomy remained uncertain until recent times. The Crevalle Jack complex is now recognized as three species; Caranx hippos in the Atlantic, Longfin Crevalle Jack Caranx fischeri in the Eastern Atlantic (sympatric with C. hippos), and Pacific Crevalle Jack Caranx caninus in the Pacific (Smith-Vaniz and Carpenter 2007).   
The Crevalle Jack represents a common morphological adaptation for rapid and efficient swimming. The streamlined body, deeply forked caudal fin, narrow caudal peduncle, and scutes that form a lateral caudal keel all contribute to reduced resistance during swimming. In fact, the swimming mode is named carangiform swimming. Carangiform swimming is a type of cruising in which approximately half to two thirds of the body is not very flexible and bends only slightly during swimming.  The back third provides the forward thrust propelling the fish forward. Carangiform swimming allows for high sustained swimming speed, but not quite as fast as tunas, marlin, and sailfish. It is very difficult to study the realized maximum sustained swimming speed in the wild and most reports of swimming speeds are not to be trusted.  Consequently, we don’t really know how fast a Crevalle Jack can swim in the wild.  If we apply 4.5 body lengths/s from lab experiments of Dickson et al. (2012), one would extrapolate that a 1 meter long Crevalle Jack could swim at 4.5 meters/sec for 30 seconds -- more than enough to bend your rod tip. 
Tail motion in carangiform fish from Liu and Hu (2010).
Liu and Hu (2010) studied the carangiform swimming mode in order to simulate motion control in a bionic fish.  This is more difficult than one might imagine. It requires separate motion control algorithms for cruising and maneuvering.  Cruising is swimming at a constant linear or angular speed, whereas maneuvering involves actions such as acceleration, deceleration, quick turning, up/down motions, and hovering. 
 Robotic fish  from Liu and Hu (2010).
Adult Crevalle Jacks feed on schools of small fish and schools of Crevalle Jacks work to trap baitfish at the surface, creating a feeding frenzy.  This video  from Florida Fish and Wildlife Conservation Commission shows how a school of Crevalle Jacks have trapped many Pinfish Lagodon rhomboides nearshore.   Typically, schools of Crevalle Jack will corner a school of baitfish at the surface and feed with commotion that can be seen at great distances. Crevalle jacks are common in both inshore waters and the open sea, and they feed mainly on small fish.
Crevalle Jack. Photo by Brett Albanese
Crevalle Jacks may be found inshore or offshore and often schooling with other jacks, though larger specimens (up to 5 feet) are often solitary.   Life history of Crevalle Jack is all about growing fast, producing many small eggs, and breeding in large aggregations in estuaries and inshore reefs. Eggs ride the currents and the small larvae are pelagic and as they grow and develop.  Juveniles are associated with buoys and Sargassum weed, a behavior known as ‘piloting’ (Hunter and Mitchell 1968).  Juveniles have a deeper body form than adults and have 5 dark bars that remain until the fish reaches about 6 inches in size.    
Illustration of juvenile Crevalle Jack at 15.3mm.  From Berry 1959.
Crevalle Jacks are a popular game fish. Because they are open water predators that chase prey fish to the surface, anglers can target Crevalle Jacks. Any fast-moving fish-mimicking lure will do. Their adaptations for swimming mean they put up a powerful fight for their size and often fight to exhaustion.  The Texas record is 52.25 inches, 50.25 pounds.  Sport anglers typically practice catch and release and are encouraged to resuscitate fish to minimize release mortality.   Increase the odds they will live to fight again!
Release of captured Crevalle Jack.  Source
Crevalle Jack have good quality flesh, as long as they are bled immediately.  Caranx species are important to artisanal fishers in many tropical regions.  Further, they have great aquaculture potential in Brazilian waters as they are well adapted to captivity in near-shore cages (Rombenso et al. 2016). 
Berry, F.H. 1959.  Young jack crevalles (Caranx species) off the southeastern Atlantic coast of the United States. Fishery Bulletin 59:417-535.
Dickson, K.A., J.M. Donley, M.W. Hansen, and J.A. Peters. 2012. Maximum sustainable speed, energetics and swimming kinematics of a tropical canangid fish, the green jack Caranx caballus. Journal of Fish Biology 80:2494-2516.  
Hunter, J.R., and C.T. Mitchell. 1968. Field experiments on the attraction of pelagic fish to floating objects.  Journal du Conseil - Conseil Permanent International pour l'Exploration de la Mer 31(3):427-434.
Liu, J., and H. Hu. 2010.  Biological inspiration: From carangiform fish to multi-joint robotic fish.  Journal of Bionic Engineering 7:35-48.
Rombenso, A.N., J.C. Bowzer, C.B. Moreira, and L.A. Sampaio. 2016.  Culture of Caranx species [Horse-eye Jack Caranx latus (Agassiz), Blue Runner Caranx crysos (Mitchill), and Crevalle Jack Caranx hippos (Linnaeus)] in near-shore cages off the Brazilian coast during colder months. Aquaculture Research 47:1687-1690.
Sánchez-García, C., O. Escobar-Sánchez, M. Candelaria Valdez-Pineda, J.S. Ramírez-Perez, R.E. Morán-Angulo, and X.G. Moreno-Sánchez.  2017.  Selective predation by crevalle jack Caranx caninus on engraulid fishes in the SE Gulf of California, Mexico.  Environmental Biology of Fishes 100:899-912.
Smith-Vaniz, W.F., and K.E. Carpenter. 2007. Review of the crevalle jacks, Caranx hippos complex (Teleostei: Carangidae), with a description of a new species from West Africa. Fishery Bulletin 105:207–233.

Saturday, February 24, 2018

Will Social Media Empower Fisheries Students Via Learning Networks? By Don Orth

I raised this question in a recent article in Fisheries. I contend that social media can be used effectively to encourage student development and facilitate the utility of personal learning networks.  Students and others must join in and create the new networks to meet their needs.  I suggested that five pedagogies will benefit students greatly if they and their instructors choose to use them.  These are public writing, Twitter and infographics, digital storytelling, online communities, and electronic portfolios.   Educators must assist students in this quest for change.    Refer to the article for a complete discourse with scholarly references. {email me at, if you have access issues.}  

The key element for this to work is development of digital learning networks (aka communities of practice).  Online networks facilitate a “just-in-time” connection with experts. One recent example on Facebook (TM) comes from the All Fish Species Identification group.  With over 2,000 members who are respected fish experts or specialists with identification of many fish families, this is the “go to” group when you have a difficult fish to identify.  Photographer Irvin Calicut recently posted a photo of a heron with a fish and asked "What fish is this?"   Within two days the fish was identified by member, Grégoire Germeau -- the Grunting Toadfish Allenbatrachus grunniens.    This is only one of many online communities that are being formed every day.  
Heron with unidentified fish. Photo by Irvin Calicut
Students in Ichthyology class are archiving photos and drawings from their notebooks to the Ichthyology Class at VT site on Flickr.   As we transition into new fish groups, students follow others on Flickr and invite them to add photos to our photo pool.  Witness the addition of a Yellowtail Snapper Ocyurus chrysurus by a professional photographer.   The work of experts and novices come together on one network. 

Student work gets better over time and there is a record of their early efforts as well as improved sketches, annotations, and photos as the term progress.  Social media does not have to make students stupid. Social media is a venue for sharing results of deeper learning activities or exposing shallow learning.  As John Dewey wrote many years ago, “Education is a social process; education is growth; education is not preparation for life but is life itself.”  
Photos posted in Ichthyology Class atVT Flickr site.  A. closeup of Northern Hogsucker Hypentelium nigricans; B. Breeding tubercles of Bluehead Chub Nocomis leptocephalus; C. Cartilaginous ridge of Central Stoneroller Campostoma anomalum. Photos by D.J. Orth.
Learning can be fun.  I know students find it hilarious to watch me struggle to sketch a fish on the whiteboard.  Even funnier to listen to me translate some lessons as musical parodies, such as Learn Your Fishes Well  and others. Writer Anne Lamott wrote “Perfectionism is the voice of the oppressor, the enemy of the people. ... and it is the main obstacle between you and a shitty first draft.”  Students realize that the first “shitty” draft is expected.  However, if final essays are posted online on the Virginia Tech Ichthyology blog, then the students have a broader public audience for their writings and incentives to revise.  Students also reflect on their struggles during Ichthyology class and create digital stories.  These digital stories evolved out of practical processes for resolving issues, educating ourselves, and pursuing our goals, while combining traditional and emerging literacies.  A quick search of “On Becoming An Ichthyologist” on YouTube returns some online stories; here’s one.  Many traditional class assignments can be readily updated to use online tools, such as meme generators, infographics, Instagram, Twitter, or Facebook.  Memes are internal representations of knowledge that are culturally inherited through sharing and “fish memes” are a favorite assignment.
Example fish meme assists the student in remember new family name

We have a key role to play in training fisheries students in the communications of fisheries issues for multiple, diverse audiences in open-access media.  Our youngest college students are entirely different than 20th century students.  In fact a 10-year old, Henry Foster, wrote to Arkansas leaders with suggestions for the state fish of Arkansas, which led to #GARkansas on Twitter, and an online petition to make the Alligator Gar the official state fish of Arkansas.  

In summary, the answer to the question is "YES" -- Social media will empower students.  However, we all have be engaged to create authentic online learning networks.  To join the network, visit us at Virginia Tech Ichthyology.  

Orth, D.J.  2018.  Social media may empower fisheries students via learning networks.  Fisheries  DOI: 10.1002/fsh.10034

Saturday, February 17, 2018

Clingfish Are Powerful Clingers in the Intertidal Zone, by Don Orth

Clingfish (Gobiesocidae) are the super suckers of the fish world! They spend their entire lives in the intertidal zones.  These nearshore waters have high, variable forces from crashing waves and strong water currents in marine intertidal environments. Clingfish are small (3-5 inches) and must hang on tight.  This family of fishes includes about 140 benthic fish species in 36 genera occurring in all major oceans and also in freshwater habitats. 
 Northern Clingfish Gobiesox maeandricus, Photo by Alison Young
Clingfish are so successful in the intertidal zone because they evolved modified pelvic fins to create a suction disc that acts as a morphological aid to resist the wave action.

Ventral sucking disc of the clingfish, showing epidermal papillae along disc margin.  Illustration by Green and Barber (1988)
But how does it cling so tight?  Super suction is made possible by the fusion of pelvic and pectoral fins to form special suction cup that can be flexed (Green and Barber 1988).  The suction disc also has a specialized epithelium, or microvilli.  Professor Adam Summers, University of Washington's Friday Harbor Laboratories, says these "thin hairs that are the same aspect ratio and length as the hairs on geckos’ feet or spiders’ toes or beetles’ feet.”   Papillae consist of tightly packed rods, which are divided into tiny filaments at the tips (Wainwright et al. 2013).  But these microvilli adhere underwater. When attaching to a surface, the fish rocks its pelvic girdle, forcing water out from under the disc and creating an area of sub-ambient pressure.  I call that “Suck Power!”
Clingfish adhering to a rock (a) is due to tiled papillae at the edge of the disc (b) and papillae are divided into fine filaments at the tips (c and d and zoomed-in SEM images).  (Wainwright et al. 2013). 
Clingfish do not simply hold fast in one location all the time. So the adhesive disc must work fast, be reversible and work on surfaces fouled by algae and encrusting organisms. This allows the clingfish to move in different ways.  Clingfish use a variety of feeding strategies to capture a diet of crustaceans and limpets Clingfish must also move to court, mate, and protect their offspring.  Pires and Gibran (2011) described how the clingfish moves by sliding the sucker disk across each stone, which is a slow form of movement.   The other movement type was “surfing” where the clingfish takes advantage of the ebbing tide and quickly moves a greater distance.  Clingfish are not good swimmers, so the ventral sucking disc is essential for moving around the intertidal zone.   Clingfish move over the entire shelter stone surface (see below for sequence of movements 1 through 8) and even rotate the body under the stone (b).  
Standard movements observed in a clingfish Gobiesox barbatulus (Pires and Gibran 2011).

Scientists devise ways of measuring everything.  Clingfish are capable of generating adhesive forces equal to 80 to 230 times their body weight, forces greater than engineered suction cups (Ditsche et al. 2013).  Watch the power of the suction disk to pick up 300 times its body mass. Why does anyone study clingfish sucking morphology?  It just might provide inspiration to the problem of creating a reversible approach to adhering to irregular, submerged surfaces.  So next time you are at the sea shore, turn over some rocks and observe these amazing little clingfishes.  


Ditsche, P., D.K. Wainwright, and A.P. Summers. 2014. Attachment to challenging substrates – fouling, roughness and limits of adhesion in the northern clingfish (Gobiesox maeandricus). The Journal of Experimental Biology 217:2548-2554  doi:10.1242/jeb.100149
Green, D.M., and D.L. Barber. 1988. The ventral adhesive disc of the clingfish, Gobiesox maeandricus: integumental structure and adhesive mechanisms.  Canadian Journal of Zoology 66:1610-1619.
Pires, T.H.S., and F.Z. Gibran. 2011.  Intertidal life: field observations on the clingfish Gobiesox barbatulus in southeastern Brazil.  Neotropical Ichthyology 9(1):233-240.
Wainwright, D.K., T. Kleinteich, A. Kleinteich, S.N. Gorb, and A.P. Summers. 2013. Stick tight: suction adhesion on irregular surfaces in the northern clingfish. Biology Letters 9: 20130234.

Friday, February 9, 2018

What Are Umbrella Fish? by Don Orth

“What's an umbrella fish?” a young student asked me.  Stumped, I replied “Never heard of one.”  The question bugged me until a library search confirmed there was no “umbrella fish.”  However, in conservation biology the term ‘umbrella’ species is one of several buzzwords used for surrogate species. Surrogate species may indicate biological diversity or environmental change or simply connect in the public’s imagination regarding habitat protection. Surrogate buzzwords include focal species, indicator species, keystone species, umbrella species, target species, foundation species, flagship species, and ecological engineer species (Caro 2010).   Even if the terms are loosely used, the species-centered conservation approaches can promote public awareness and raise funds for conservation. If it works, use it. 

Flagship species are primarily intended to promote public awareness and to raise funds for conservation. While flagship species are selected for their marketing value, umbrella species are selected based on ecological criteria and are expected to benefit a wide range of co-occurring species (Caro 2010; Kalinkat et al. 2017). Is it possible to select flagship umbrellas to describe species that explicitly integrate both functions?  Perhaps. The classic giant panda (Ailuropoda melanoleuca) is a popular charismatic species used since the 1960s by World Wildlife Fund for Nature for fundraising as well as it benefits for co-occurring endemic species.  
Recently, Kalinkat et al. (2017) identified over 60 potential freshwater flagship umbrella species.  So, there could be an umbrella fish. The next phase must be to implement and evaluate conservation strategies based on the flagship umbrella species approach.  Do the flagship umbrella species attract public attention and funding for conservation?  Is the diversity of co-occurring communities protected? We don’t know.

Emmanuel Frimpong (2018) argues that our lack of knowledge perpetuates ineffectual conservation practices in tropical Afrotropical freshwater fishes. We need to understand which fishes are rare and which are common and how the species may interact in aquatic ecosystems. His experiences, studying Nocomis breeding and nest associates, confirmed that seven species of cyprinids may breed on Nocomis nests. Therefore, Nocomis may be an umbrella species, but conservation action may take time.  His story emphasizes to us all that understanding the ecology and natural history of individual species is essential to adopting the language of flagship umbrella species.  That is one thing holding us back in fish conservation efforts. Frimpong (2018) then asks “Can we protect these rare species without protecting the common species that function as their hosts?”  Probably not!
A Bluehead Chub Nocomis leptocephalus guards his breeding mound in Toms Creek, Virginia.  Photo by Emmanuel Frimpong. 
We have yet to see if the flagship umbrella species approach develops and spurs effective conservation programs.  However, the concept of an umbrella is an important one. However, the multiple individual values and motivations around fish conservation should be embraced within a large, inclusive umbrella community of conservationists.  Here I review a few of these potential umbrella fish. Remember, while umbrella species may not exist for all systems, they may be effective in some.  Therefore, the concept is important to consider further to promote conservation action.

The Humphead Wrasse Cheilinus undulatus (also known as the Napoleon Wrasse) shares habitat with a diverse community in coral reefs. The species has a broad geographic distribution in the Indo-Pacific Ocean, a region with tremendous coral reef biodiversity. Like most wrasses (Labridae), the Humphead Wrasse is a protogynous hermaphrodite, meaning they will start life as females and may transition to males. As a large, conspicuous coral reef fish that is severely overfished, it fits the criteria for a flagfish species.  Most tropical marine protected areas (MPA) are too small to effectively protect the Humphead Wrasse and a significant scaling up of MPA is required (Weng et al 2015).  Protecting the Humphead Wrasse would protect many co-occurring species with shared habitat requirements.  Therefore, it may be both a flagship and an umbrella species.
Humphead Wrasse.  Photo by Paolo Macorig.  
Asian Arowana Scleropages formosus (Müller & Schlegel, 1844) is also known as the Golden Dragonfish or Golden Arowana. These fish are so highly valued by the aquarium trade that they are seldom eaten. Yet, the native swamps and sluggish rivers in southeast Asia are highly altered and the entire aquatic ecosystem and its services are at risk.  This recognizable and charismatic fish may be an appropriate flagship umbrella species.
Asian Arowana. Photo by Marcel Bulkhead. 
The largest salmonid in the world is the highly migratory Taimen or Huchen Hucho hucho.  The Taiman, known to locals as the “river god’s daughter,” may reach up to six feet and weigh up to 200 pounds.  Overfishing and habitat change reduced populations that once thrived throughout Mongolia and Siberia (Geist et al. 2009).   Since sport anglers value the large, unique fish, the Taimen is the target species in creating a large catch-and-release fishing reserve.  Read more here.
The Arapaima is one of the largest freshwater fishes and can reach 8 feet in length.  However, throughout it range in Brazil and Guyana it seldom reaches that large size anymore due to overfishing. One of the most heavily exploited fishes in South America, even today, scientists are not certain how many species of Arapaima exist (Stewart 2013a, 2013b; Watson et al. 2016).  While it fits some requirements for a flagship species, whether it’s an umbrella species will require more studies. 
Arapaima sp.  Photo by 
The Mekong river and delta regions support a highly diverse ecosystem, which is heavily dammed.  Biodiversity of the Mekong basin is second only to the Amazon basin.  New fish species are described from the Mekong regularly and no other river has so many species of very large fishes. These include giant freshwater stingray Himantura polylepis, several giant barbs (Catlocarpio saimensis and Probarbus spp), and giant catfishes.  Two catfishes, the Mekong Giant Catfish (Pangasianodon gigas) and the Striped Catfish (Pangasianodon hypophthalmus) are candidate flagship umbrella species (So et al. 2006). Fish make up ½ to 2/3rd of the diet of rural people of the Mekong and 2/3rd of the people are engaged in wild capture fisheries so conservation of these areas is critically important.    
Mekong Giant Catfish (left) and  striped catfish Planet Catfish (right) 
Mahseer (Tor spp; Cypriniformes: Cyprinidae) are large-bodied, migratory freshwater fishes that are endemic to the monsoonal rivers of Asia. They are flagship species because of their economic, recreational and conservation interests.  Six of eighteen species of Tor are endangered, while others are threatened or data deficient (Pinder et al. 2015). Mahseers are referred to as “kings of aquatic systems” and are the primary targets of recreational anglers.  Fishing guides and recreational anglers have a stake in the protection of the catchments that support populations of Mahseer (Bower et al. 2017), yet the value of Mahseers as umbrella species has not been assessed.
Dekkan Masheer Tor khudree  Photo by J. F. Helias 
In North America, sturgeons (Acipenseridae), American Eel, Pacific salmonids, and Brook Trout are potential flagship umbrella species.   Brook trout Salvelinus fontinalis are well studied and a variety of conservation planning tools have been developed.  Many tools designed to characterize the continuum of viability, habitat condition, and vulnerability of Brook Trout populations may also protect a wide variety of co-occurring species.   

Sturgeons and Paddlefish in North America are possible flagship umbrella species.  In 2012, the North American Sturgeon and Paddlefish Society formed to focus on “current declines in sturgeon and paddlefish populations across North America, NASPS is dedicated to promoting the conservation and restoration of these species by developing and advancing research pertaining to their biology, management, and utilization.”   There are many threats that are specific to individual species of sturgeon. While study methods are improving, conservation efforts are playing a game of catch up. Perhaps a flagship umbrella species approach can help protect essential riverine habitats for hackelbacks.    
Although the status of American Eel is unclear, but one thing is clear.  American Eels may be hindered from reaching up to 84% of upstream habitats, thereby fragmenting the single, panmictic population.  Efforts to restore connectivity may benefit a large number of co-occurring fishes.
Four species of cyprinids that are nest associates with Bluehead Chub nests.  Photo by Derek Wheaton. 
We have a difficult challenge in conserving the fishes and their habitats.  Pluralism is the rule in conservation in general and fish conservation in particular. Many approaches, many values, and many types of people must be engaged in the process (Cooke et al. 2013).  Green et al. (2015) advocated for creating a much larger community that is strengthened, rather than factionalized, by pluralistic viewpoints.  Local and large-scale activities are important to our conservation efforts.  If the concept of flagship umbrella species can assist in making conservation more effective, then we should pursue the idea vigorously.

Bower, S.D., A.J. Danylchuk, R. Raghavan, S. C. Danylchuk, A.C. Pinder, A.M. Alter, and S. J. Cooke. 2017.  Involving recreational fisheries stakeholders in development of research and conservation priorities for mahseer (Tor spp.) of India through collaborative workshops.  Fisheries Research 186:665-671.
Caro, T. 2010. Conservation by proxy: Indicator, umbrella, keystone, flagship, and other surrogate species.  Island Press. 
Cooke, S. J. et al. 2013. Failure to engage the public in issues related to inland fishes and fisheries: strategies for building public and political will to promote meaningful conservation. Journal of Fish Biology 83(4):997-1018.
Frimpong, E. A. 2018. A case for conserving common species. PLOS Biology 16(2): e2004261
Geist J, Kolahsa M, Gum B, Kuehn R. 2009. The importance of genetic cluster recognition for the conservation of migratory fish species: the example of the endangered European huchen Hucho hucho (L.). Journal of Fish Biology 75(5):1063-1078.
Green, S. J., J. Armstrong, M. Bogan, E. Darling, S. Kross, C.M. Rochman, A. Smyth, and D. Verissimo.    2015.  Conservation needs diverse values, approaches, and practitioners.  Conservation Letters doi: 10.1111/conl.12204
Hogan, Z.S. 2011. Ecology and conservation of large-bodied freshwater catfish: a global perspective. American Fisheries Society Symposium 77:39–53.
Kalinkat, G. and seventeen coauthors. 2017. Flagship umbrella species needed for the conservation of overlooked aquatic biodiversity.  Conservation Biology 31:481-485.
Kalinkat, G. and seventeen coauthors. 2017. Flagship umbrella species needed for the conservation of overlooked aquatic biodiversity.  Conservation Biology Supplemental file.  18 pp.
Pinder AC, Raghavan R, Britton JR. 2015. Efficacy of angler catch data as a population and conservation monitoring tool for the flagship Mahseer fishes (Tor spp.) of Southern India. Aquatic Conservation: Marine and Freshwater Ecosystems 25(6):829-838. 204
So, N., J.K. Van Houdt, and F.A. Volckaert. 2006. Genetic diversity and population history of the migratory catfishes Pangasianodon hypophthalmus and Pangasius bocourti in the Cambodian Mekong River. Fisheries Science 72(3):469-476. 237
Stewart, D. J. 2013a. Re-description of Arapaima agassizii (Valenciennes), a rare fish from Brazil (Osteoglossomorpha: Osteoglossidae). Copeia 2013:38–51.
Stewart, D. J. 2013b. A new species of Arapaima (Osteoglossomorpha, Osteoglossidae) from the Solimões River, Amazonas State, Brazil. Copeia 2013:470–476.
Watson, L.C., D.J. Stewart, and A.M. Kretzer. 2016.  Genetic diversity and population structure of the threatened giant Arapaima in southwestern Guyana: Implications for their conservation. Copeia 104:864-872.
Weng, K.C., M.W. Pedersen, G.A. Del Raye, J. E. Caselle, and A. E Gray.  Umbrella species in  marine systems: using the endangered humphead wrasse to conserve coral reefs.  Endangered Species Research 27:251-263.