Callorhinchus milii

Geographic Range

Callorhincus milii , also known as elephant fishes, elephant sharks, ghost sharks, or whitefish, have a fairly selective range. Found in the South Pacific, they prefer the continental shelves of temperate waters. They are primarily found along the southern coast of Australia, and in the waters surrounding Tasmania and New Zealand. There are a few reports of them in the rivers of South Africa and Tasmania, and along the southwestern coast of South America.

• Biogeographic Regions
• pacific ocean pacific ocean
  • native native

Habitat

Although mostly found in shallow waters 30 to 200 m in depth, elephant fishes have also been found at depths of greater than 600 m. C. milii primarily live on coastal continental shelves, but females seasonally move to shallower waters to lay eggs.

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• coastal coastal

Physical Description

Callorhinchus milii are silver in color, and often have irregular dark blotches on the sides and fins. They have a distinctive flexible, trunk-like projection at the tip of the snout. This “trunk” has earned them the name elephant fishes or elephant sharks despite the fact that they neither true fish nor shark. C. milii is a type of chimaera , a cartilaginous fish related to sharks and rays. Other characteristics include an elongate body, presence of an anal fin, an arched caudal fin, and two widely spaced dorsal fins. The first fin has a serrated spine at its front, and the second is relatively tall with a short base compared to other chimaera species. Mature males exhibit a unique head clasper, an erupted tenaculum on a pre-pelvic clasper, and large calcified pelvic claspers.

A feature unique to elephant fishes ( Callorhincidae ) that should be noted is that unlike all other chimaera species, they have a very well developed rectal gland. The rectal gland is crucial in regulating osmotic conditions in the body of the fish. It is thought that since elephant fishes migrate for mating and may encounter water with varying salinity, they developed a rectal gland superior to that of other chimaeras. While all other chimera species are found in deep water habitats, this adaptation may allow elephant fishes to successfully inhabit more shallow coastal waters.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Development

Embryonic development is divided into 36 stages followed by hatching. These stages are determined by assessment of morphological characteristics including but not limited to length, amount of pigmentation, eye development, and head flexure. Rostral bulb size is used primarily when classifying embryos from stages 17-29 while tail length, gill filament size, and snout development are used to identify more mature embryo specimens. While early characteristics are more notable from one stage to the next, later stage assignment is often made more complex by less distinction between the characteristics of each stage. Hatchlings are fully developed and look just like miniature adults upon emergence from the egg case.

From the time they hatch at about 10 cm until they reach a length of approximately 50 cm, elephant fishes grow in a linear fashion. At this length males are mature. However, the female growth then accelerates to about twice the rate of males until they reach sexual maturity at about 70 cm in length. Maturity is reached in males at about 3 years of age and in females at 4 to 5 years of age.

Reproduction

Males have a pair of retractable head claspers, pre-pelvic claspers, and calcified claspers to help hold the female during copulation. The head and pre-pelvic claspers are unique to C. milii and are not found in other species of Chondrichthyes >. Females have a “sperm pouch” to store spermatic material. Actual mating behavior remains undocumented.

Adult fishes migrate to the shallower waters of bays and estuaries to mate between February and May. C. milii is oviparous, meaning they produce eggs that hatch outside the body. Females also have a “sperm pouch” to store spermatic material. Large, flat egg-cases containing a single embryo are deposited on muddy or sandy substrate. When released, egg-cases are yellow, but slowly turn brown or black. A female lays two eggs about a week apart that develop for 6 to 8 months. Embryos feed on the yolk until they hatch.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous
• sperm-storing sperm-storing

Callorhinchus milii exhibit little parental investment. Female fishes invest in egg yolk for the nourishment of the embryo, but otherwise eggs are left behind in shallow water and juveniles emerge on their own in 6 to 8 months.

• Parental Investment
• pre-fertilization
  • provisioning

Lifespan/Longevity

Maximum recorded age in the wild is fifteen years from a tag return, but dorsal fin spine growth increments indicate maximum size to occur at about nine years. No age data has been recorded for C. milii in captivity.

Behavior

Behavior has not been extensively observed in elephant fishes since they live in a less accessible habitat, but seasonal migration for mating has been well documented in the shallow coastal areas that are more populated by people. Elephant fishes are not known to be a social species. However, fishermen report separate catches of males and females in the same areas suggesting the sexes segregate in the wild when not reproducing.

• Key Behaviors
• natatorial natatorial
• motile motile
• migratory migratory

Home Range

Evidence of territorial behavior or the size of the home range has not been documented in C. milii .

Communication and Perception

Elephant fishes have large eyes, and also use their unique “trunk” for perception. It is covered with sensory pores that can detect movements and small electrical impulses. This allows the animal to find prey hidden in the substrate. Social communication between individuals has yet to be investigated.

• Communication Channels
• visual visual
• chemical chemical

• Perception Channels
• visual visual
• vibrations vibrations
• chemical chemical
• electric electric

Food Habits

Callorhincus milli is a carnivorous species. Elephant fishes probe the substrate with the plow-shaped protrusion on their snout to find food. They primarily feed on mollusks and shellfish including the clam species Maorimactra ordinaria .

• Primary Diet
• carnivore carnivore
  • molluscivore molluscivore

• Animal Foods
• mollusks
• aquatic or marine worms
• aquatic crustaceans

Predation

Callorhinchus milii is subject to predation by larger fish and sharks such as the broadnose sevengill shark ( Notorynchus cepedianus ). Elephant fishes are actively fished for food by humans as well. It's coloration is probably cryptic.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Elephant fishes are secondary consumers that help may affect the populations of primary consumers through predation. Although they are predators, they provide a food source for tertiary consumers as well. Elephant fishes thus play an intermediate role in the food web linking small organisms like filter feeders to large apex predators.

Callorhincus milii is susceptible to parasites like Callorhynchicola multitesticulatus and Gyrocotyle rugosa .

Economic Importance for Humans: Positive

Elephant fishes are caught both commercially and recreationally and are often marketed as "whitefish." They are often used as the fish in “fish and chips” meals in Australia and New Zealand. Recently humans are also using C. milii in genetic research as model organisms to learn more about the evolution of cartilaginous fishes and the early ancestors of all vertebrates.

• Positive Impacts
• food food
• research and education

Economic Importance for Humans: Negative

Elephant fishes very little threat to humans. The dorsal spine may cause injury to fisherman, but otherwise there are no known adverse effects of Callorhinchus milii on humans.

Conservation Status

Callorhinchus milii is relatively abundant throughout the waters of southern Australia and New Zealand and was listed as a species of Least Concern by the IUCN Red List of Threatened Species in 2003, the last date of review. Commercial fishing reports showed that catch rates remained stable for roughly 20 years prior to that reivew. A total allowable catch (TAC) has been imposed on C. milii in both Australia and New Zealand to limit catch numbers. Subsequent work found that some stocks in Australia were being overfished, in part due to previously undocumented recreational fishing taking breeding females near shore (Bracchini et al., 2008).

Some elephant fishes may also take refuge in marine protected areas that are closed to fishing.

Other Comments

Lately, C. milii have become a focus of genetic study. In 2013 the elephant fish became the first cartilaginous fish to have its entire genome sequenced. Cartilaginous fishes are the sister group to bony vertebrates, and elephant fishes are some of the most primitive and slowly developing of these organisms, so their genetic information can hopefully provide new insights into how jawed vertebrates evolved. The C. milii genome may also provide new information regarding bone formation and adaptive immunity in higher organisms. So far, genetic evidence has shown that humans actually share more similarities with these ancient chondrichthyans than with more modern bony fish .

Additional Links

Encyclopedia of Life

Contributors

Kayla Boyes (author), Indiana University-Purdue University Fort Wayne, Mark Jordan (editor), Indiana University-Purdue University Fort Wayne.

References

Allen, T. 1999. The Shark Almanac . New York, New York: The Lyons Press.

Anonymous, 2014. "Elephant Shark (Australian Ghostshark) Callorhinchus milii " (On-line). Carnivora Forum. Accessed April 01, 2014 at http://carnivoraforum.com/topic/10017715/1/ .

Barnett, A., K. Redd, S. Frusher, J. Stevens, J. Semmens. 2010. Non-lethal method to obtain stomach samples from a large marine predator and the use of DNA analysis to improve dietary information. Journal of Experimental Marine Biology and Ecology , 393: 188-192.

Bester, C. 2010. "Ghost Shark" (On-line). Ichthyology at the Florida Museum of Natural History. Accessed April 01, 2014 at http://www.flmnh.ufl.edu/fish/Gallery/Descript/ghostshark/ghostshark.html .

Didier, D., E. LeClair, D. VanBuskirk. 1998. Embryonic staging and external features of development of the chimaeroid fish, Callorhinchus milii (Holocephali, callorhinchidae). Journal of Morphology , 236: 25-47.

Ferrari, A., A. Ferrari. 2002. Sharks . Buffalo, New York: Firefly Books.

Francis, M. 1997. Spatial and temporal variation in the growth rate of elephantfish ( Callorhinchus milii ). New Zealand Journal of Marine and Freshwater Research , 31: 9-23.

Hamlett, W., M. Reardon, J. Clark, T. Walker. 2002. Ultrastructure of sperm storage and male genital ducts in a male holocephalan, the elephant fish, Callorhynchus milii . Journal of Experimental Zoology , 292: 111-128.

Hyodo, S., J. Bell, J. Healy, T. Kaneko, S. Hasegawa, Y. Takei, J. Donald, T. Toop. 2007. Osmoregulation in elephant fish Callorhinchus millii (Holocephali), with special reference to rectal gland. The Journal of Experimental Biology , 210: 1303-1310.

Last, P., J. Stevens. 2009. Sharks and Rays of Australia . China: CSIRO Publishing, Australia.

Mullo, D. 2013. "Elephant Fish ( Callorhinchus milii )" (On-line). Wildfish. Accessed March 31, 2014 at http://wildfish.co.nz/portfolio/elephant-fish/ .

Reardon, M., T. Walker, M. Francis. 2003. " Callorhinchus milii " (On-line). www.iucnredlist.org. Accessed March 31, 2014 at http://www.iucnredlist.org/details/41743/0 .

Sullivan, K. 1977. Age and growth of the elephant fish Callorhincus milii (Elasmobranchii: Callorhynchidae). New Zealand Journal of Marine and Freshwater Research , 11 (4): 745-753.

Vankatesh, B., A. Lee, V. Ravi, A. Maurya, M. Lian, J. Swann, Y. Ohta, M. Flajnik, Y. Sutoh, M. Kasahara, S. Hoon, V. Gangu, S. Roy, M. Irimia, V. Korzh, I. Kondrychyn, Z. Lim, B. Tay, S. Tohari, K. Kong, S. Ho, B. Lorente-Galdos, J. Quilez, T. Marques-Bonet, B. Raney. 2014. Elephant shark genome provides unique insights into gnathostome evolution. Nature , 505: 174-179.

Fisheries Victoria, State of Victoria, Australia. Evaluation of effects of targeting breeding elephant fish by recreational fishers in Western Port.. ISBN: 1 74146 935. Queenscliff, Victoria, Australia: Fisheries Research Brand. 2008. Accessed July 06, 2015 at http://www.depi.vic.gov.au/fishing-and-hunting/fisheries/publications-and-resources/fisheries-reports/your-licence-fees-at-work-reports/2003-2008/evaluation-of-effects-of-targeting-breeding-elephant-fish-by-recreational-fishers-in-western-port .