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Hippocampus kudaCommon seahorse

By Micheleen Hashikawa

Geographic Range

Hippocampus kuda is strictly a marine species, widely distributed throughout the Indo-Pacific region, from the Indian Ocean to the northwestern, western central, and eastern central areas of the Pacific Ocean ("Project Seahorse", 2003; Foster et al., 2003). Approximately 23 countries have confirmed the native presence of H. kuda, ranging from Australia to China (Lourie et al., 2004). Because spotted seahorses are popular ornamental aquarium fish, their captive distribution has become global (Lally and Hough, 1999). ("The biology of seahorses", 2003; Foster, et al., 2003; Lally and Hough, 1999; Lourie, et al., 2004)

Habitat

Generally, H. kuda inhabit shallow inshore areas with an average depth of 0 to 8 m, but they have also been found at a maximum depth of 55 m (Lourie et al., 2004). They can be found in mangroves, coastal seagrass beds, estuaries, coastal bays and lagoons, harbors, sandy sediments in rocky littoral zones, and rivers with brackish waters (Lourie et al., 2004; Job et al., 2002). Spotted seahorses have also been found attached to drifting Sargasssum as far as 20 km from shore (Foster et al., 2003). (Foster, et al., 2003; Job, et al., 2002; Lourie, et al., 2004)

  • Range depth
    0 to 55 m
    0.00 to 180.45 ft
  • Average depth
    0-8 m
    ft

Physical Description

Originally, ancient Greek poets used the Greek word Hippocampus to describe a half-horse, half-fish mythical god (hippos meaning horse and campus meaning sea monster) (Lally and Hough, 1999). This description poignantly describes their horse-like head positioned 90 degrees from its upright, armor-plated body, curved trunk, and prehensile tail ("Project Seahorse", 2003). Spotted seahorses can have an all black, grainy textured body pattern or a creamy, pale yellow body spotted with large, dark circles. These colors and patterns can be changed temporarily to match their immediate surroundings and act as a camouflage to avoid predators (Lourie et al., 1999). ("The biology of seahorses", 2003; Lally and Hough, 1999; Lourie, et al., 1999)

Spotted seahorses are morphologically conservative and lack typical physical features of fishes such as pelvic and caudal fins, teeth, and a stomach (Lourie et al., 1999; "Project Seahorse", 2003). They also lack scales, having a layer of skin stretched over a series of bony plates instead which are visible as rings around the trunk ("Project Seahorse", 2003). These visible rings are useful in identifying various Hippocampus species. ("The biology of seahorses", 2003; Lourie, et al., 1999)

Hippocampus kuda can be distinguished from other seahorses by the presence of low, rounded bumps instead of the typical spines found along the body ("Project Seahorse", 2003). Spotted seahorses have a characteristically thick snout and deep head (Lourie et al., 2004). On either side of the deep head are eyes that can move independently, allowing them to maximize the search range when hunting for prey ("Project Seahorse", 2003). An adult H. kuda male can be distinguished from a female by the presence of a brooding pouch on his belly. ("The biology of seahorses", 2003; Lourie, et al., 2004)

Seahorse lengths are measured by recording the distance from the tip of the tail to the top of the coronet, a cup-like depression found on top of the head. Adult lengths of H. kuda typically range between 7.0 and 17.0 cm (Capuli, Torres, and Froese, 2004). Adult weights, on the other hand, vary with the reproductive stages of both males and females ("Project Seahorse", 2003). ("The biology of seahorses", 2003; Capuli, et al., 2004)

  • Sexual Dimorphism
  • sexes shaped differently
  • Range length
    7 to 17 cm
    2.76 to 6.69 in

Development

Eggs are fertilized by the male and become embedded in the pouch wall as they are deposited into the brooding pouch by the female through the ovipositor (“Project Seahorse”, 2003). The male may carry between 20 to 1000 eggs in its pouch (Tchi Mi, Kornienko, and Drozdov, 1996). Although fertilized eggs contain a small amount of yolk, they undergo typical teleost egg cleavage and developmental processes, which lasts for approximately 20 to 28 days. Larval development stops one week prior to the time at which they are released into the open waters. ("The biology of seahorses", 2003; Tchi Mi, et al., 1996)

The timing of labor in males varies depending upon species, water temperature, monsoon patterns, and lunar cycles ("Project Seahorse", 2003). However, most males go into labor at night during a full moon. Males engage in vigorous pumping and thrusting motions for several hours to release the young. Juvenile seahorses emerge from the pouch as independent, miniature adults. The average length of H. kuda at birth is 7 mm. ("The biology of seahorses", 2003)

In general juvenile seahorses can be distinguished from their adult counterparts by differences in body proportions (Lourie et al., 2004). Young seahorses have larger heads, slimmer, spinier bodies, and higher coronets. In captivity, H. kuda have been observed to reach full maturity in 14 weeks, growing at a rate of .9 to 1.53 mm per day (Job et al.,2002). (Job, et al., 2002; Lourie, et al., 2004)

Reproduction

Spotted seahorses maintain a faithful association with only one partner (Clayton, 2003). A new mate is sought only when a partner dies. Seahorses in general have a complex mating system, which is characterized by a unique courtship ritual (John G. Shedd Aquarium, 2004). The male begins by changing its color patterns as it dances around the female. It also produces clicking sounds with its coronet. The pair proceeds with the ritual by entwining their tails together and floating across the ocean floor. Eventually the male and female face each other belly-to-belly at which time the female places her eggs into the male’s brooding pouch with her ovipositor. This courtship ritual is modified and repeated daily even after the male has become pregnant. Each morning the pair comes together to dance, change colors, and entwine tails. (Clayton, 2003; "Oceanic Seahorse", 2004)

The age at which female and male H. kuda reach sexual maturity is unknown ("Project Seahorse", 2003). However the presence of a brooding pouch on the male - the site where the male carries the fertilized eggs- signifies male sexual maturity. Breeding occurs year round (John G. Shedd Aquarium, 2004). A female may return to lay a new batch of eggs in her partner's pouch the same day that juveniles are released. Gestation generally occurs within 20 to 28 days (Lourie et al., 2004). The maximum reported brood size is 1405, but a brooding pouch may contain anywhere from 20 to 1000 fertilized eggs. Generally only 100 to 200 juvenile seahorses are actually produced per pregnancy (Lally and Hough, 1999). ("The biology of seahorses", 2003; "Oceanic Seahorse", 2004; Lally and Hough, 1999; Lourie, et al., 2004)

  • Breeding interval
    Breeding may occur every 20 to 28 days.
  • Breeding season
    Breeding occurs year round.
  • Range number of offspring
    1405 (high)
  • Average number of offspring
    20-1000
  • Range time to hatching
    20 to 28 days
  • Range time to independence
    20 to 28 days
  • Average age at sexual or reproductive maturity (female)
    14 weeks
  • Average age at sexual or reproductive maturity (male)
    14 weeks

Like other seahorses, H. kuda has an unusual mode of reproduction where the female provides the eggs but the male carries and cares for the embryos in its brooding pouch ("Project Seahorse, 2003). While the male carries its brood for 20 to 28 days, the developing larvae are constantly nourshied with a placental-like fluid that is secreted within its pouch. This fluid removes waste products and supplies the fertilized eggs with oxygen and nutrients. As the pregnancy proceeds, the placental fluid gradually changes its chemical content and becomes more similar to the surrounding seawater. This fluid change minimizes the shock newborns experience when they hatch and are released into an environment with higher salt content. These newly released juveniles are fully independent and do not require any parental care once they leave the brooding pouch. ("The biology of seahorses", 2003)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • male
    • protecting
      • male

Lifespan/Longevity

The natural lifespan of H. kuda and its relatives are virtually unknown ("Project Seahorse", 2003). Lab and aquatic observations estimate 3 to 5 years for larger seahorse species and 1 year for smaller species. ("The biology of seahorses", 2003)

  • Typical lifespan
    Status: captivity
    1 to 5 years

Behavior

Spotted seahorses are poor swimmers and generally remain anchored to substrates using their prehensile tails (Lally and Hough, 1999). Seahorses are generally solitary, except for their mates, and are active during the day. (Lally and Hough, 1999)

In general pairs remain in close proximity to one another and avoid associations with non-pair individuals (Clayton, 2003). (Clayton, 2003)

Home Range

Hippocampus species typically have narrow home ranges due to their poor swimming abilities (Clayton, 2003). They tend to remain close to a holdfast within their territory. Holdfasts and home ranges are only changed in an event of a partner's death or habitat destruction. (Clayton, 2003)

Communication and Perception

Monogamous pairs can often be found coiled together or within close proximity to one another (Clayton, 2003). Pairs communicate daily during male pregnancy to reinforce their relationship. (John G. Shedd Aquarium, 2004) The first few stages of the mating ritual are repeated, which include changing body color patterns, dancing, and making clicking sounds. This implies they they communicate through visual cues, sounds, and through touch. Seahorses also perceive their environment with these same senses. (Clayton, 2003; "Oceanic Seahorse", 2004)

Spotted seahorses are able to maximize their perception of potential prey and predators by moving their eyes independently of each other ("Project Seahorse", 2003). ("The biology of seahorses", 2003)

Food Habits

Spotted seahorses are ambush predators and thrive only on live, moving food (Lally and Hough, 1999; “Project Seahorse”, 2003). They have large appetites and feed mainly on zooplankton, small crustaceans, and larval fishes. Because they are poor swimmers, H. kuda utilize their thick snouts and specialized jaws to suck in their prey (“Project Seahorse”, 2003). ("The biology of seahorses", 2003)

  • Animal Foods
  • fish
  • aquatic or marine worms
  • aquatic crustaceans
  • zooplankton

Predation

Humans are the primary predators of H. kuda because of their large economic importance ("Project Seahorses", 2003). There are few natural predators of adult seahorses due to their unpalatable bony-plated bodies and their ability to avoid predation through camouflage. However, they have been found in the stomachs of loggerhead sea turtles, tunas, and dorados. Skates, rays, and crabs have also been observed to prey on seahorses. ("The biology of seahorses", 2003)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Seahorses in general can act as food items for many larger fish, crustaceans, and water birds ("Project Seahorse", 2003). Adult seahorses themselves are voracious predators and will suck and swallow any animal that will fit in their mouths. ("The biology of seahorses", 2003; Zhang, et al., 2003)

Economic Importance for Humans: Positive

Spotted seahorses are the most valuable species in the traditional Chinese medicine trade (TCM) due to their large size, smooth texture, and pale complexion when dried (Project Seahorse et al, 2003). According to traders, TCM books, and recent pharmacological studies, seahorses can regulate urinogenital, reproductive, nervous, endocrine, and immune systems as well as mimic certain hormones related to aging, tumor development, and fatigue (Zhang et al., 2003). None of these uses, however, have been tested. The global consumption of seahorses for medicinal purposes during the year 2001 alone has been estimated at 25 million seahorses or 70 metric tones (“Project Seahorse”, 2003). ("The biology of seahorses", 2003; Foster, et al., 2003; Zhang, et al., 2003)

Spotted seahorses are very popular among aquatic collectors as a favorite aquarium fish (Lally and Hough, 1999). Over 51 nations and territories are involved in buying and selling H. kuda and its relatives (Job et al., 2002). The largest known exporters of seahorses are Thailand, Vietnam, India, and the Philippines, and the bulk of seahorses are fished from the Indo-Pacific region (Xu et al., 2003). (Job, et al., 2002; Zhang, et al., 2003)

Seahorses are fascinating to many people and diving trips to see seahorses, as well as other fish, are important in marine ecotourism.

Economic Importance for Humans: Negative

Spotted seahorses have no negative effects on humans.

Conservation Status

Spotted seahorses are listed as vulnerable under the World Conservation Union’s IUCN Red List and are on the CITES Appendix II (Lally and Hough, 1999). Population numbers of H. kuda in the wild are unknown but scientists, conservationists, and traders agree that populations have declined by at least 30% due to habitat destruction, pollution, bycatch, trades in traditional Chinese medicine, curios, and aquaria (Lally and Hough, 1999; Project Seahorse et al, 2003). There is little legal oversight or regulation on trading, and few countries require permits (Lally and Hough, 1999). (Foster, et al., 2003; Lally and Hough, 1999)

Scientists predict further declines in H. kuda population without immediate intervention (Lally and Hough, 1999). Implementing effective conservation methods has been hampered by confusion over H. kuda taxonomy, which has been driven by the difficulty in morphologically distinguishing them from their relatives, their ability to camouflage, current lack of descriptions, and unestablished, independent naming designations (Lourie et al., 1999). Taxonomic definitions must be established first before researchers can confidently understand the biology, ecology, and relative abundance of spotted seahorses. (Lourie, et al., 1999)

Seahorse farming is currently being developed as an alternative strategy to conserve native seahorse populations while helping fishers to continue earning a sustainable income (Job et al., 2002). Initial research of H. kuda’s ability to grow and survive appears very promising, but further research is needed to determine whether aquaculturing of the spotted seahorse on a more larger scale effectively meets the high market demand while preventing further depletion of native populations. (Job, et al., 2002)

Other Comments

Both wild and cultured H. kuda are susceptible to Costia disease infections, a protozoan parasite (Capuli, Torres, and Froese, 2004). (Capuli, et al., 2004)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Micheleen Hashikawa (author), University of Michigan-Ann Arbor, William Fink (editor, instructor), University of Michigan-Ann Arbor.

Glossary

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

fertilization

union of egg and spermatozoan

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

planktivore

an animal that mainly eats plankton

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

John G. Shedd Aquarium. 2004. "Oceanic Seahorse" (On-line). John G. Shedd Aquarium. Accessed November 19, 2004 at http://www.sheddaquarium.org/sea/fact_sheets_print.cfm?id=90.

2003. "The biology of seahorses" (On-line). Project Seahorse. Accessed October 21, 2004 at www.projectseahorse.org.

Capuli, E., A. Torres, R. Froese. 2004. "fishbase.org" (On-line). Accessed October 14, 2004 at http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=5955&genusname=Hippocampus&speciesname=kuda.

Clayton, B. 2003. "Welfare implications of the commercial use of seahorses Hippocampus sp." (On-line). Veterinary Education and Information Network. Accessed November 19, 2004 at http://vein.library.usyd.edu.au/links/Essays/2003/clayton.html.

Foster, S., A. Marsden, A. Vincent. 2003. "Hippocampus kuda" (On-line). The IUCN Red List of Threatened Species. Accessed October 22, 2004 at http://www.redlist.org/search/details.php?species=10075.

Job, S., H. Do, J. Meeuwig, H. Hall. 2002. Culturing the oceanic seahorse, Hippocampus kuda. Aquaculture, 214: 333-341.

Lally, K., P. Hough. 1999. Seahorses - A Forgotten Species. Reef Research, 9 (3): 1-2. Accessed November 18, 2004 at http://www.gbrmpa.gov.au/corp_site/info_services/publications/reef_research/issue3_99/rr_pg31-32.html.

Lourie, S., S. Foster, E. Cooper, A. Vincent. 2004. Guide to the Identification of Seahorses. Washington D.C.: University of British Columbia and World Wildlife Fund. Accessed October 14, 2004 at http://www.projectseahorse.org/.

Lourie, S., J. Pritchard, S. Casey, S. Truong, H. Hall, A. Vincent. 1999. The taxonomy of Vietnam's exploited seahorses (family Syngnathidae). Biological Journal of the Linnean Society, 66: 231-256.

Tchi Mi, P., E. Kornienko, A. Drozdov. 1996. "Embryonic and Larval Development" (On-line). Russian Journal of Marine Biology. Accessed November 19, 2004 at http://www.maik.rssi.ru/cgi-bin/search.pl?type=abstract&name=marbio&number=5&year=98&page=325.

Zhang, N., B. Xu, C. Mou, W. Yang, J. Wei, L. Lu, J. Zhu, J. Du, X. Wu, L. Ye, Z. Fu, Y. Lu, J. Lin, Z. Sun, J. Su, M. Dong, A. Xu. 2003. Molecular profile of the unique species of traditional Chinese medicine, Chinese seahorse (Hippocampus kuda Bleeker). Federation of European Biochemical Socieites Letters, 550: 124-134.

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