the spimy dogfish

Squalus Acanthias is the scientific name for the spiny dogfish, while Mustelus Canis is the scientific name for the smooth-skinned dogfish. Mandarin dogfish, Cuban dogfish, and Angola dogfish are all members of the same Squalidae family as the spiny dogfish. They are classified as chondrichthyes and classified as squaliformes. (Shark Savers) Formalized adverbial adverb

Spiny dogfish prefer cool to warm temperate oceans with temperatures ranging from 0 to 15 degrees Celsius. They are mainly benthic in nature and can be found up to 900 meters deep near the seabed or in sedimentary areas. They will, however, rise to the surface when necessary. Spiny dogfish can tolerate the difference in water salinities and therefore be found both inshore and offshore. They are densely populated around Canadian costal oceans of the Atlantic and Pacific Oceans. On the western Atlantic Ocean, the distribution is from Greenland to Argentina, including the Mediterranean, Black and Red Sea while on the eastern side it is found in the southern part of South Africa. (Bester)

Smooth skinned dogfish, on the other hand prefer to live in-shores and around bays. It also prefers shallow water at around 18 meters although they can survive up to 200 meters. They are also sometimes found living in freshwaters albeit for short durations. Their geographical distribution is centered mainly in areas at the east coast of America of the Western Atlantic Ocean as well as around the Caribbean Sea and at parts of Southern Brazil. (Bester)

One of the distinguishing features of the spiny dogfish is that there have no anal fin and have easily seen white spots that are scattered on its body surface. The other distinguishing feature is that the dorsal fins of the spiny dogfish are preceded by a spine. (Bester)

The greatest anthropogenic threat to the spiny dogfish are due to fisheries motivated by human appetite. The spiny dogfish is hunted for its liver to manufacture liver oil as well as for its fins to make a much popular Chinese delicacy “sharks fin soup”. Lately, the spiny dogfish has also been consumed widely as food among the human population. (ShARCC)

The shark’s skin had a rough texture that is abrasive. When I rubbed the sharks towards the tail, it was smooth. However, in the opposite direction, I could feel the roughness of the skin.

Under microscope, the skin looked like scale in the form of tiny teeth projections. The scales on the spiny dogfish are known as placoid scales and are also called dermal denticles. The skin looks like this under microscope:

Placoid Scales

Label of the outside feature of the shark is as below:

Eyes

Anterior dorsal fin

Posterior dorsal fin

Caudal fin

Gills

Pelvic fin

Pectoral fin

Cloaca is known as the opening that the kidneys, intestines and genitals empty into. Thus the benefit of the shark having it is to dispose waste materials such as urine and feces to the outside and to disseminate sperm into the female if it is a male and to receive semen from a male if it is a female for reproduction.

The shark I had was a male spiny dogfish with testes. The paired testes were located dorsal to the liver at the ventral end of the body cavity and were elongated in oval shape.

The liver was located at both sides of the shark body when dissected. There were two lobes of liver, one on each side, longitudinal in shape that extended to almost the full length of the body cavity. The spleen was located near to the anterior end of the intestinal area and posterior to the stomach cavity and is somewhat triangular in shape.

There were some remnants left in the stomach when dissected. It looked to be digested material that was loose, greyish and soft in touch.

The shark has the following sensory organs. The eyes, located at both sides to the rostrum is used for eyesight. The nostrils, located underside at the ventral end of the rostrum permits the shark to detect odors through it. As for the most powerful sensory network located just beneath the nostrils is the Ampulla of Lorenzini. It has the capability of detecting a number of changes, such as temperature difference, water salinity and water pressure.

Rugae are intestinal mucosa folds found on the stomach surface. They increase the surface area in the stomach for better and faster food absorption.

The spiral valve is a modified ileum located within the shark’s intestines. The spiral valve is twisted intestines that aid sharks to digest and absorb nutrients due to its shorten intestines.

The spiny dogfish has an appetite for fishes that humans eat, such as herring, mackerels, squid, shrimp, sea cucumber, crabs and octopus. The female spiny dogfish reaches maturity slower than its male counterparts at 12 years of age compared to 6 years for males. (Campana et al) The nocturnal smooth skinned dogfish, on the other hand prefers diets make up of crustaceans, such as shrimps, lobsters, crabs and small fishes. Similar to the spiny dogfish, the female smooth skinned dogfish reaches sexual maturity later than the males, at 4-5 years of age whereas the males achieve sexual maturity in 2-3 years. (Bester)

Works Cited

Bester, Cathleen. “Squalus Acanthias”. University of Florida, Florida Museum, N.d, https://www.flmnh.ufl.edu/fish/discover/species-profiles/squalus-acanthias. Accessed 28 March 2017.

Bester, Cathleen. “Mustelus Canis”. University of Florida, Florida Museum, N.d, https://www.flmnh.ufl.edu/fish/discover/species-profiles/mustelus-canis. Accessed 28 March 2017.

Campana, S.E., Warren Joyce and David W.Kulka. Growth and Reproduction of Spiny Dogfish off the Eastern Coast of Canada, Including Inferences on Stock Structure. Biology and Management of Dogfish Sharks, American Fisheries Society 2009, pp.195-208.

N.p. “Dogfish Sharks”. Shark Savers, 2017, http://www.sharksavers.org/en/education/biology/different-types-of-sharks/dogfish-sharks/. Accessed 28 March 2017.

N.p. “Spiny Dogfish Sharks”. Sharks of the Atlantic Research and Conservation Coalition, ShARCC, 2011, http://atlanticsharks.org/shark_species_details.php?id=5. Accessed 28 March 2017.

Ritter, E.K. “Fact Sheet: Spiny Dogfish”. Shark Info, April 2016, http://www.sharkinfo.ch/SI2_99e/sacanthias.html. Accessed 28 March 2017.