About Seahorses

About Seahorses


Seahorse Biology

Seahorses are one of God’s most fascinating and mysterious creatures. The amazing thing is that they are not a myth as many people believe. Their unique, majestic charm has captivated mankind for centuries. They are sometimes difficult to find in the wild, except by experienced divers, due to their chameleon-like ability to change colour and camouflage with their habitat. It is not surprising that new species continue to be found as more research is conducted.

Classification

Seahorses are classed as a fish in the family Syngnathidae , which also includes seadragons and pipefish. They clearly do not look like your typical fish with curling ‘pre-hensile’ tails that clasp seagrasses and other suitable objects, their elongated horse-like head and their lack of scales. They are the only fish with a neck. The long tubular "nose" of the seahorse, seadragons and pipefishes is actually a fused jaw from which the family name Syngnathid is derived.

The exact number of seahorse species around the world is unknown, though Kuiter (2000) suggests the number to be in the order of 60, of which 25 are found in Australia. They are found in temperate, sub-tropical and tropical marine waters around the globe. Some species are estuarine while others inhabit coastal environments.

Feeding

The fused jaw of the Syngnathids acts like a suction gun when prey is being eaten and is fully equipped with a ‘pressure release valve’ on top of the head, associated with the gills. When prey floats past, the seahorse closely examines it and then in a flash, strikes and sucks it into its mouth. They are not fast swimmers so it is more of an ambush on the unsuspecting shrimp. Larger shrimps may be attacked by a number of seahorses and consumed in stages as the shrimp’s softer body parts are targeted. As seahorses do not have the capacity to store food for extended periods in their stomach, regular feeding throughout the day is required.

Life Cycle

Believe it or not, it is the male Seahorse who gets pregnant and gives birth to live young. This seems to be a very pleasing attribute to many females of the human kind! An elaborate courtship dance is undertaken where the male and female gracefully bow their heads towards one another and then swim together in an almost synchronised side-by-side dance. In some species the males go pale in the body and dark along the front of the chest. In the Potbelly seahorse the male swells his belly full of water as if to say to the female – hey look at me I am the one for you and can take all your eggs! Eventually the female faces the male positioning the ovipositor (egg depositor) over the opening at the top of his pouch, which he is able to stretch open. Eggs are deposited in the pouch and it is believed they are fertilised externally while being deposited. He closes the pouch and depending on the species, temperature and other factors, between 3-6weeks later the baby seahorses are born. In the wild it seems that birth is usually at first light. The biggest counted birth from a single male at Seahorse Australia has been 1116 baby seahorses. Some of the large species with smaller babies may even have more.

It seems that a male only receives eggs from a single female although sometimes there may be more than one egg exchange.

Different species have different size babies. Sometimes smaller varieties like H. whitei have bigger babies that the larger species like H. kuda . They are on their own from birth and unlike many newly hatched fish which have a larval stage; seahorses are ready for food from the first day.

Habitat

Most seahorses typically live in seagrass and seaweed environments rather than on coral reefs. They are not strong swimmers, so they will hold on to anything they can with their prehensile tails. Corals may sting seahorses and cause them problems. Nevertheless some more specialised species can be found on coral reefs such as the spectacular Hippocampus bargibanti .

Other features

Seahorses have a varying capacity to change colour but do not seem to turn blue or green. Colour changing may occur for different reasons including camouflage and courtship.

They move forward with the dorsal fin on the centre of their back and have two pectoral fins behind the gills which help them to steer.

While regarded a fish, they lack scales and feature bony plated skin which is a very flexible type of armour.

Rudie Kuiter in his book "Seahorses, Pipefishes and Their Relatives" suggests there are more than 60 species of seahorse worldwide, but the number is in debate. CITES regulators recognise about 48 species, although this is constantly under review. Australia has up to 25 species (Kuiter 2001) with new species still being identified from time to time. Below is a brief summary of the Australian species as described by Kuiter (2001):

  • Hippocampus minotaur (Bullneck seahorse). Southern NSW, Bass strait.
  • Hippocampus bargibanti (Pygmy seahorse). Australia (QLD) to Japan.
  • Hippocampus jugumus (Collared seahorse). Only known from 1 specimen off Lord Howe Island
  • Hippocampus kampylotrachelos (Smooth seahorse). Indonesia and Timor Sea. Australian specimen known from Ashmore Reef (WA).
  • Hippocampus dahli (Low-crown seahorse). Coastal waters from Moreton Bay (QLD) to Darwin.
  • Hippocampus planifrons (Flat-face seahorse). Only known from Shark Bay and Broome (WA).
  • Hippocampus biocellatus (False-eyed seahorse). Shark Bay (WA) in shallow algae or weedy reef habitats from the intertidal zone to 20m depth.
  • Hippocampus breviceps (Short-head seahorse). South Australian Gulfs, Bass Strait and Tasmania.
  • Hippocampus tuberculatus (Knobby seahorse). Perth to Onslow (WA).
  • Hippocampus taeniopterus (Common seahorse). Moluccan seas, Papua New Guinea, Darwin, tropical waters off the east coast (from about Brisbane north).
  • Hippocampus tristis (Sad seahorse). Northern NSW, southern QLD and Lord Howe Island.
  • Hippocampus alatus (Winged seahorse). Northern Australia from WA to Cape York and Papua New Guinea.
  • Hippocampus queenslandicus (Queensland seahorse). Queensland coast (inner reef waters).
  • Hippocampus semispinosus (Half-spined seahorse). Uncertain, but possibly off the northwest shelf of Australia.
  • Hippocampus abdominalis (Eastern Potbelly seahorse). Eden to Newcastle NSW and New Zealand.
  • Hippocampus bleekeri (Southern Potbelly seahorse). Known as ‘Southern Knights’ in the Australian aquarium industry. Very similar to H. abdominalis and previously grouped as the same species. South Australia, Bass Strait and Tasmania.
  • Hippocampus zebra (Zebra seahorse). Beautifully striped seahorse known only from a few specimens off the Queensland coast and Milne Bay Papua New Guinea.
  • Hippocampus montebelloensis (Monte Bello seahorse). Only known from Monte Bello Island and Exmouth Gulf in WA.
  • Hippocampus whitei (White’s seahorse). Estuaries and harbours of NSW.
  • Hippocampus procerus (High-crown seahorse). Southern QLD in algae reefs.
  • Hippocampus elongatus (West Australian seahorse). West coast north to about Kalbarri.
  • Hippocampus spinosissimus (Hedgehog seahorse). Unconfirmed in Australia. Sapeh Strait, Komodo.
  • Hippocampus multispinus (Northern Spiny seahorse). NW Western Australia and Northern Territory, also known from Milne Bay, Papua New Guinea.
  • Hippocampus histrix (Thorny seahorse). Widespread species (Japan to Indonesia and New Caledonia) but not formally known from Australia yet.
  • Hippocampus hendriki (Eastern Spiny seahorse). Great barrier reef QLD.
  • Hippocampus angustus (Western Spiny seahorse). Central Coast of Western Australia.
  • Hippocampus grandiceps (Big-head seahorse). Known only from the QLD side of the Gulf of Carpentaria.

References: Kuiter R.H. (2000) Seahorses Pipefishes and Their Relatives. TMC Publications.

Kuiter, R.H. (2001) Revision of the Australian Seahorses of the Genus Hippocampus (Syngnathiformes: Syngnathidae) with Descriptions of Nine New Species. Records of the Australian Museum 53:293-340.

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