Give Thanks to the Spiny Dogfish, Squalus acanthias. By Don Orth

We should be grateful for our many fishy blessings on Thanksgiving. The Spiny Dogfish Squalus acanthias plays many roles in our world. It may be a bloody nuisance for commercial fishermen, but Spiny Dogfish once provided abundant fish oil and vitamin A.  Today they are a substitute fish for fish n chips. Why the dogfish even has its name on a brewery.  Through history, the Spiny Dogfish has posed many challenges. To the Spiny Dogfish and those who helped to overcome the challenges, we give thanks. 

Spiny Dogfish is the representative of the cartilaginous fishes (Chondrichthyes) that is dissected in anatomy labs throughout the world. Each year biology majors and pre-med students are challenged in comparative vertebrate anatomy lab before advanced study in human anatomy.  Here students dissect the dogfish shark and begin to compare organ systems among the chordates. Students name structures and consider their functional adaptations.   At night they review and cram from 3-pound dissection guides, such as Wischnitzer (2006) or Fishbeck and Sebastiani  (2015).   

Dissection of Spiny Dogfish in process in Ichthyology Lab. Photo: DJ Orth

The body of the Spiny Dogfish is slim with a narrow pointed snout and asymmetrical caudal fin lobes. Spiny Dogfish are slate gray on the dorsal surface and sides, and have characteristic white spots and a white belly.  The irregular white spots are typical of younger fish and may be lacking on older individuals.  It has two widely separated dorsal fins and two sets of paired fins.  It lacks an anal fin – how do you explain that? Maybe God meant for Ichthyology Professors to have a little fun with student lab practicals?  "Label the anal fin on this specimen."

Squalus acanthias (female 678 mm TL) from Ebert et al. (2010)

Commercial fishers are challenged to harvest high-valued fishes without catching unpopular dogfish. Spiny Dogfish grow to 3.3 (males) to 4 feet (females) and adults school near the bottom where they overlap with many more valuable food fishes, such as cod, halibut, flounder, and sole. When these valuable groundfish were overfished in the late 1980’s (Buchsbaum et al. 2005), commercial fishermen targeted the larger female Spiny Dogfish, leading to overharvest.  Spiny Dogfish are not the first choice of fishermen, and are an impediment to harvesting groundfish, such as the Silver Hake (aka, whiting) Merluccius bilinearis.  Trawlers targeting whiting use a small mesh trawl with a raised footrope to avoid catching some unwanted bottom fishes. However, the Spiny Dogfish is still captured with this gear.  An excluder grate installed on the trawl net reduces the catch of Spiny Dogfish and subsequent handing time and harvests more of the target fish. 

Dogfish excluder grate on a hake trawl.   Photo from Chosid et al. (2012)

Surprisingly, the naming was another challenge. Carolus Linnaeus first named the Spiny Dogfish in 1758.  Since that time 24 other species of Squalus have been discovered and named. For example, in 1854, Charles Girard named the North Pacific Dogfish, Squalus suckleyi.  Like many other complex taxonomic issues, reasonable people may disagree until careful measurements of meristic and morphometric measurements and genetic data from representative samples are analyzed.  In 1960, the American Fisheries Society committee on names of fishes, grouped the disconnected North Pacific and Atlantic populations into a single species Squalus acanthias, ignoring the work of Girard. It took 50 years before Ebert et al. (2010) examined meristic, morphological, and molecular data and resurrected the endemic North Pacific Squalus suckleyi.  Consequently, there is some confusion around names used in previous literature.  Further, there are still many other species of Squalus that need to be evaluated in order to understand the phylogeny of the the dogfish genus, Squalus.

The common name, dogfish, has always been a challenge.  It just doesn't sound like a chef’s delicacy. The name, dogfish, was been used since the 15^th century as fishermen observed them hunting in packs.   Dokefyche is a middle English word that combines “dog” and “fish.”   Cabinet makers in the 19^th century used the skins of dogfish to polish hardwoods.  Livers were also used by tanneries. Fisheries still considered the dogfish a trash species in the mid 20^th century. Harvest was used for livestock and pet feed or fish meal.  However, the liver is high in natural vitamin A and fisheries once harvested the dogfish and used the liver oil to derive vitamin A. 

Many years ago it was marketed as Flake, Grayfish, Cape Shark, Japanese Halibut, or Rock Salmon.   Like all marine elasmobranchs, the Dogfish maintains osmotic balance with its external environment with a mixture of urea and trimethyl amine oxide (TMAO) in its blood stream.  Otherwise they would lose freshwater to the marine environment and be unable to function. So that urea thing may keep you from ever trying a Dogfish entrée. But do try it. Just remember Dogfish must be bled, gutted, and iced immediately after harvest to avoid the urea settling in the tissues.  Watch the cleaning video. Soon after death, bacteria can quickly convert the urea in their blood and tissue into ammonia.  Yuk!  The taste of ammonia is not appealing, in fact, it's a sign of kidney disease!  So prepare the dogfish correctly and even consider marinating dogfish in something slightly acidic.  The result will be another delectable dish, thanks to the Spiny Dogfish.

Spiny Dogfish, although once overfished in the Northwest Atlantic, are now the largest shark fishery in US. The Spiny Dogfish is often maligned by commercial and recreational fishers and its role is misunderstood.  Also, the leading edge of their dorsal spine is a big, white, needle-sharp spine, a formidable weapon capable of inflicting agonizing pain. Bigelow and Schroeder (1948) in Fishes of the Western Atlantic, wrote “from a practical aspect the spiny dog in the Western Atlantic is chiefly important because it is undoubtedly more destructive to gear and interferes more with fishing operations than does any other fish – shark or teleost.”    

Spiny Dogfish are opportunistic feeders, preying on what is locally abundant.  They feed primarily on crustaceans when young, and move on to comb jellies, jellyfish, squid, and fish as they get larger.  Consequently, they are blamed for competing with valuable groundfish for food. They also eat commercially valuable fishes, such as mackerel, herring, and squid.   Ctenophores (comb jellies)  have become more prevalent in diets of Spiny Dogfish between 1981 and 2000; this increase likely reflects increased abundance of ctenophores (Link and Ford 2006; Ford and Link 2014).  Spiny Dogfish are slow growing and there are many predators on the Spiny Dogfish, including the Cod, Red Hake, Goosefish, larger sharks, seals, and orcas.   Many fisheries management decisions today are still made without quantifying many of these key ecosystem interactions (Murawski 2000).

Although Spiny Dogfish are not the most desirable fish in the sea, there is high demand in the United Kingdom for Fish n Chips and in Germany for a Beer Garden Snack, called shillerlocken.   Shillerlocken should not to be confused with the pastry named after the same German poet. Schaumrollen, or Schillerlocken, is something my grandfather Orth made in his bakery each Christmas.  It’s ironic that Spiny Dogfish are now protected under EU fishing regulations to stop it being caught and sold with chips, but it is legal to sell it in the UK provided it has been caught outside the EU and imported. 

 

Spiny Dogfish becomes the fish in "Fish n Chips"  Photo by Alamy (Source)

Changing demands on the Spiny Dogfish led to historical fluctuations in abundance. It is clear now from their life history, that the Spiny Dogfish is vulnerable to rapid overharvest without controls on harvest. Spiny Dogfish are difficult to age.  Validation of methods for examining annual marks on the spines or vertebrae were only recently validated via radiocarbon dating (Campana et al. 2006).  

Annual rings on the spines of Spiny Dogfish (from Campana et al. 2006, left) and on sectioned and stained vertebra (from Bubley et al. 2012,  right)

Growth and maturity studies indicate slow growth, late maturity, and low fertility.  Spiny Dogfish are viviparous and the embryos, called pups, feed off their yolk sac until parturition. The gestation period is long and fertility is low; gestation is 18 to 22 months.  Therefore, females give birth every other years to between 2 and 15 pups (average: 6).  The maximum reported size is 117 cm (=46 inches) total length and maximum reported age is 40 years. 

Growth (left, Bubley et al. 2012) and maturity, as measured by the female gonadosomatic index, of Spiny Dogfish (right, Bubley et al. 2013)

Fisheries scientists estimate population size and the removals from targeted fisheries and discards from bycatch. Large trawls are used to estimate catch per swept area and population size.  However, the Spiny Dogfish school and often school just ahead of the trawls.  Therefore, discard mortality and abundance, derived from trawl surveys, are uncertain estimates  (Rago et al. 1998; Rago and Sosobee 2009).  Female fish dominate the harvest of Spiny Dogfish. Harvesting results in truncated size and age distributions, which further reduces population productivity. Consequently, catch limits were imposed on harvests in US waters starting in 2000. These regulations allowed the Northwest Atlantic stock of the Spiny Dogfish to rebuild (Rago and Sosobee 2011).  However, commercial interests lobby for increases in catch limits and stock assessments are updated periodically to inform future management actions.   Meanwhile, Spiny Dogfish stocks in the eastern Atlantic are dwindling, which puts demands on Spiny Dogfish populations from US fisheries.  So challenges will continue. 

Remember to give thanks to the following on this Thanksgiving Day:  the Spiny Dogfish in your comparative anatomy lab, Carolus Linnaeus for naming the Spiny Dogfish, modern taxonomists for getting the names right, inventors for the dogfish excluder grate, fisheries biologists for revealing the life history of Spiny Dogfish, population analysts for trying to get the population numbers right, and fisheries managers for acting to limit harvests and sustain fisheries.  

References

Bubley, W.J., J. Kneebone, J.A. Sulikowski, and P.C.W. Tsang. 2012. Reassessment of spiny dogfish Squalus acanthias age and growth using vertebrae and dorsal-fin spines.  Journal of Fish Biology 80:1300-1319.

Bubley, W.J., J.A. Sulikowski, D.M. Koester, and P.C.W. Tsang. 2013.  Using a multi-parameter approach to reassess maturity of spiny dogfish, Squalus acanthias, following increased fishing pressure in the western North Atlantic.  Fisheries Research 147:202-212.

Buchsbaum, R., J. Pederson, and W. E. Robinson, editors. 2005. The Decline of Fisheries Resources in New England: Evaluating the Impact of Overfishing, Contamination, and Habitat Degradation. MIT Sea Grant College Program Publication No. 05-5.  

Campana, S. E., C. Jones, G.A. McFarlane, and S. Myklevoll.   2006. Bomb dating and age validation using the spines of spiny dogfish (Squalus acanthias). Environmental Biology of Fishes 77, 327–336.

Chosid, D.M., M. Pol, M. Szymanski, F. Mirarchi, and A. Mirarchi. 2012.  Development and observations of a spiny dogfish Squalus acanthias reduction device in a raised footrope silver hake Merluccius bilinearis trawl.  Fisheries Research 114:66-75.

Dell'Apa, A., C.W. Bangley, and R.A. Rulifson. 2015. Who let the dogfish out? A review of management and socioeconomic aspects of spiny dogfish fisheries.  Reviews in Fish Biology and Fisheries  DOI: 10.1007/s11160-014-9379-1

Ebert, D.A., W.T. White, K.J. Goldman, L.J.V. Compagno, T.S. Daly-Engel, and R.D. Ward. 2010. Resurrection and redescription of Squalus suckleyi (Girard, 1854) from the North Pacific, with comments on the Squalus acanthias subgroup (Squaliformes: Squalidae). Zootaxa 2612, 22–40.  

Fishbeck, D.W., and A. Sebastiani. 2015. Comparative Anatomy: Manual of Vertebrate Dissection 3rd Edition. Morton Publishing Company, 576 pp. 

Ford, M.D., and J.S. Link. 2014. Bounds on biomass estimates and energetic consequences of Ctenophora in the Northeast U.S. Shelf ecosystem. International Journal of Oceanography http://dx.doi.org/10.1155/2014/851809

Link, J. S., and M. D. Ford. 2006.  Widespread and persistent increase of Ctenophora in the continental shelf ecosystem off NE USA. Marine Ecology Progress Series 320:153–159

Murawski, S. A. 2000.  Definitions of overfishing from an ecosystem perspective.  ICES Journal of Marine Science 57:649-658.

Rago, P.J., K.A. Sosebee, J.K.T. Brodziak, S.A. Murawski, and E.D. Anderson. 1998. Implications of recent increases in catches on the dynamics of Northwest Atlantic spiny dogfish (Squalus acanthias). Fisheries Research 39, 165–181.   

Rago, P. J. and K. A. Sosebee. 2009 The agony of recovery: Scientific challenges of Spiny Dogfish recovery programs. pp 343-372. In V. F. Gallucci, G. A. McFarlane and G. G. Bargman eds. Biology and Management of Dogfish Sharks. American Fisheries Society, Bethesda Maryland.

Rago, P. and K. Sosebee. 2011.  Update on the status of Spiny Dogfish in 2011and initial evaluation of alternative harvest strategies. Mid Atlantic Fishery Management Council Science and Statistical Committee 

Wischnitzer, S. 2006. Atlas and Dissection Guide for Comparative Anatomy 6th Edition. W.H. Freeman, 368 pp.

Ten fish to try when you get bored with fish and chips, by Don Orth

What is the most consumed fish in the world?  If you guessed “Tuna,” then you are correct.  I think, probably.   But beyond Tuna, the most popular fish eaten depends on where you live.   Salmon, rohu, tilapia, cod, catfish, and trout are very popular, just not worldwide favorites. If you're from the Mid-Atlantic US you have likely tried Northern Snakehead, in Florida you have eaten the lionfish, Midwestern folks are learning to like or adapt to Asian Carp, and throughout North America we've been introduced to Basa, or Swai. Even if you have eaten sashimi, fish head soup, pickled herring, or caviar, it may be time for you to be more adventurous in your fish choices.  Here are ten top choices for your new fish bucket list.

10.  Lutefisk (LEWD-uh-fisk) is dried cod that has been soaked in a lye solution for several days.  This traditional dish is from Norway, Sweden, and parts of Finland.  But those in the old country do not eat it anymore. Rather it’s become a holiday treat for Scandinavian-Americans. In Scandinavia, cod were dried to preserve them for later consumption. The lutefisk origin story says that a drying rack filled with dried cod caught fire, leaving wood ashes (or lye) that changed the cod forever.  Lye is a caustic alkali that may raise the pH of the fish to 10!  Do not eat this.  To make the lutefisk edible, you must first soak the lutefisk in water to remove the lye. The soaked lutefisk is then gently poached or baked because of the jelly-like consistency.  It is an acquired taste, says the Norwegian bachelor farmer.  Others describe it as a foul and odiferous gooey fish with rancid oily taste.  Best served with lots of butter.  Uff da!

Lutefisk  Source

9. Surströmming.   If lutefisk is not an appealing fish for your bucket list, try Surströmming, which is soured herring, or its cousin Rakfisk a fermented trout. Herring, trout, and salmon are fatty fishes and drying is not an acceptable preservation method.  Fermentation, however, will preserve the fish indefinitely.

Surströmming  Source

Surströmming is only produced in northern Sweden where herring are harvested in spring, and gutted and salted.  They are then packed in barrels with a strong (17%) brine solution and allowed to ferment.  The pyloric caecum is left intact in the gutted fish. This provides proteolytic enzymes that facilitate a month-long fermentation.  The low temperatures (68̊ F) and brine are critical elements to the fermentation, which produces strong smelling acids.   It’s the smell of the surströmming that appeals to its proponents.  I mean, what else could there be to make this appealing?  Are you man enough to try it?  Closest I have gotten is watching others open a can; watch this video1 or this video2.  [Vomit Alert on video2!]

8.   Kusaya is similar to surstromming, but is a Japanese delicacy made by taking a fish like mackerel, soaking it in brine solution for a day, then laying it out in the sun for a few more days. Some kusaya makers pride themselves on having used the same brine over several generations to make their stinky fermented fish. Although the smell can be overpowering, the taste is actually quite mild.   Can't wait to try it. 

Kusaya is fermented mackerel.  Source

7.  Kæstur hákarl and Hongehoe are other versions of fermented fish.  The national disk of Iceland is the Kæstur hákarl, which is a fermented Greenland Shark.  The Greenland Shark has high content of urea and trimethylamine oxide, a mixture that facilitates osmoregulation.   However, after fermentation, the urea becomes ammonia and the hakarl has a fishy taste and an ammonia-rich smell. Andrew Zimmern, host of Bizzare Foods, described the smell as "some of the most horrific things I've ever breathed in my life."   In Korea, a skate is fermented to create a treat called Hongeohoe.  I’m told it’s edible as long as you don’t breathe. 

Hongeohoe is fermented skate.  Source

 6.  Shiokara is made from salted, fermented fish guts in a paste of malted rice. There are different varieties as you can imagine.  It can be made from whatever fish, squid, or other viscera were left over from the fishmongers shop.  This bucket list item must await travel to a specialized shiokara bar in Japan.  Tastes best when alternated with gulps of whiskey or sake.

Shiokara is salted, fermented fish guts in malted rice paste.  Source

5.  Salt cod is dried and salted so it will keep without refrigeration. When you take salt cod out of the box, you find it is hard and dry and covered in salt, not at all appealing. To make it edible again the salt cod is soaked in cold water—changing the water several times—for a couple of days until fully desalted and rehydrated.  Salt cod has a history in many countries. In Italy it's called baccalà, bacalao in Spain, morue in France, bacalhau in Portuguese, bakaliaro in Greece, saltfish in the Caribbean, and klippfisk in Scandinavian countries. The soaking process does work and the rehydrated cod can be used in any recipe calling for cod.  I recently made the Brandade de Morue recipe and can mark this one off my bucket list.  

4.  Gefilte fish are ground fish patties that were at one time stuffed back into the fish skin and baked. Gefilte fish is a Jewish tradition that later morphed into fish-shaped fish patties and even fish balls.  The gefilte fish, which is often carp, pike or whitefish, is poached in fish broth.  You can use the whole head of a large carp to make the jellied broth, or buy a prepared fish broth.  There are lots of options if you aren't planning to make it like your grandmother did. Gefilte fish is also available as a ready-to-eat product from Manischewitz. The Gefilte fish has morphed into many versions of fish meatballs.  Take ground fish (of any type), mixed with egg, breadcrumbs and herbs. Poach it very gently in salty water.

 3.  Shirako are cod sperm eaten in Japan. Romanians also eat carp milt, or Lapți, and the Russians eat herring milt, or Moloka.   Cooked or raw, fish sperm is also an acquired taste, so you may never know if you like it unless you try it.  

Shirako are cod sperm.  

 2.   Dried anchovy.   Ever eaten anchovies?   Anchovies are a healthy, sustainable food choice, that can be used in many recipes.   Cooking methods depend on their size.  Big ones are only a few inches long and are called "Dasi-myulchi" in Korean.  These are usually used for broth, while the small ones, called "Bokkeum-myulchi" are stir-fried for unique dishes. Dried anchovy can be also served without cooking as a snack. Try this spicy anchovies recipe for a snack, or Myeolchi-muchim  for a meal with rice and kimchi.     

Dried Anchovy.  Source

 And Number 1 on my bucket list? Fuguko Nuka-zuke is one rare delicacy that I haven't tried.  Fuguko Nuka-zuke are the pickled ovaries from the pufferfish.  Eating eggs of fish is much more commonplace than eating fish sperm, whether it's caviar or shad roe.  Nukazuke is a type of Japanese pickle, made by fermenting vegetables in rice bran (nuka) and fugu is Japanese for pufferfish.  How did anyone ever think to eat pufferfish ovaries?  Ovaries and other organs are filled with the deadly neurotoxin, tetrodotoxin!  Somehow the pickling process breaks down the deadly toxin.  Otherwise, the organs of the pufferfish can contain levels of tetrodotoxin sufficient to produce paralysis of diaphragm.  Do not try this one at home.

Fuguko Nuka-zuke, pickled ovaries from the pufferfish.  source

 

There are many more possibilities for your own bucket list.  You may wish to comment on this post to point out tasty items that I omitted.  I left off Ikizukuri, the practice of preparing sashimi from live seafood such as fish, shrimp or lobster.  Not raw, but live! I will say no more; I really cannot recommend that anyone try this.

The origins of many in the top ten are related to the fact that fish flesh spoils quickly.  Consequently, different cultures dried, salted, fermented fish between harvests before ice and refrigeration were widely available.  We don’t have to use these techniques today.  But we do because people find these foods interesting or tasty or both.

There are many good reasons to add more fish to your diet.  Eating more fish has been linked to lowered risk of depression, heart disease, and brain health in high-risk individuals (Marckmann and Grønbaek 1999; Morris et al. 2003; Li and Zhang 2015).  Fish provide the opportunity for a highly diverse, healthy, and interesting diet.  If you don’t like my fish bucket list, then write your own. Or you can eat bugs! 

References

Li, F., X. Liu, and D. Zhang. 2015.  Fish consumption and risk of depression: a meta-analysis.  Journal of Epidemiology and Community Health doi:10.1136/jech-2015-206278

Marckmann, P. and M. Grønbaek. 1999.  Fish consumption and coronary heart disease mortality. A systematic review of prospective cohort studies.  European Journal of Clinical Nutrition 53(8):585-590. DOI: 10.1038/sj.ejcn.1600832

Morris, M.C., D.A. Evans, J.L. Bienias, C.C. Tangney, D. A. Bennett, R.S. Wildon, N. Aggarwal, and J. Schneider. 2003.  Consumption of fish and n-3 fatty acids and risk of incident Alzheimer disease.  Archives Neurology 60:940-946.

Morris, M.C., J. Brockman, J.A. Schneider, Y. Wang, D.A. Bennett, C.C. Tangney, and O. van de Rest. 2016. Association of seafood consumption, brain mercury level, and APOE ε4 status with brain neuropathology in older adults.  Journal of the American Medical Association 315(5) doi:10.1001/jama.2015.19451