Photo StoryPublished : Mar 07, 2022Updated : Nov 15, 2022
Having evolved 25 million years ago, seahorses are unparalleled in their body structure, behaviour and ecology
Text by: Mahima Jaini
Having evolved 25 million years ago, seahorses are unparalleled in their body structure, behaviour and ecology
Seahorses are by far the most bizarre fish found on our planet— not only in appearance and behaviour but also with regard to the value humans have placed on them. Seahorses and pipefishes belong to the family Syngnathidae — slender fish with elongated snouts, small mouths, and bodies encased in bony plates. Seahorses are the only fish that swim in an upright position, having diverged from the pipefish body plan 25 million years ago.
Seahorses belong to the subfamily Hippocampinae which means “horse caterpillar”. They look very horse-like thanks to their erect posture, long necks, and downturned heads. Although they are fish, these organisms bear little resemblance to the textbook fish body shape. Seahorses lack a tail fin; most of their forward movement happens with the movement of their dorsal fin (the one on their backs). The pectoral fins (on their sides) help them turn, and their prehensile tail allows them to hold onto structures. Seahorses love wrapping their fin-less tails around plants, corals, rocks etc., standing erect with a patient, worldly demeanour.
Seahorses and some pipefish are unique. Males live-brood their juveniles. Females deposit the eggs into the male’s brood pouch, where fertilisation happens. Amazingly, there is a placental connection between the father’s body and the developing eggs, supplying the little embryos with much-needed oxygen and nutrients. The placental connection, however, is not an umbilical cord to every developing embryo — that would be a cumbersome feat as species often produce over 500 eggs. Instead, the father is connected to his developing offspring through a thin brood pouch and numerous blood vessels. Seahorses have direct development, i.e. there is no intermediate larval stage, and juveniles hatch looking much like the adult.
The seahorse’s beauty and unique appearance often lands them in the aquariums and the curio trade. Moreover, the Chinese use dry ground-up seahorses to treat a range of ailments from sore throats to sexual dysfunction. This is rather unfortunate, especially because highly effective plant-based and chemically-derived cures exist for all these problems. Turning to rare wildlife for the same disregards them as living beings that deserve to thrive on the planet, much like us.
Seahorses occur in both temperate and tropical waters. There are over 47 species found worldwide. They use their long snout to get zooplankton out of crevices. They are good at camouflage, changing colour, and blending in with their surroundings. Standing perfectly still is their forte. Often, they are found on the bottom of the seabed and, at times, even in the shallow intertidal zones, their tails wrapped around debris or seagrass. Photos: Umeed Mistry (left), Dhritiman Mukherjee (right)
If you are lucky enough, you might find a seahorse gently cruising the seabed in search of the next anchor spot. The movement of their thin — almost transparent — dorsal fin can be difficult to decipher, making it seem like they are smoothly gliding through the water without exerting any effort at all. Photo: Dhritiman Mukherjee
Seahorse eyes can move independently of each other. This allows them to view a range of directions simultaneously, increasing their ability to find prey and avoid predators. Like the eyes shown here, seahorses have very well-developed vision. Photos: Umeed Mistry
Seahorses love to hold onto things and sometimes seem very confident while doing so. (Top) The spotted or yellow seahorse (Hippocampus kuda) is hooked on a sea pen (a rare colonial animal closely related to corals and jellyfish). (Above left) This sea horse latches onto a mussel and (above right) another one hooks onto calcified Halimeda seaweed. Their upright posture helps them blend in with their surroundings, and the downturned head with fused jaws allows them to suck in small prey like zooplankton and small marine invertebrates. Photos: Umeed Mistry (top and above left), Dhritiman Mukherjee (above right)
Find the seahorse! Millions of years of evolution, make hide and seek all the more challenging. The pygmy seahorse has evolved in close association with gorgonians, a branching soft coral. In fact, the first pygmy seahorse was discovered accidentally from a collected gorgonian. Seahorse colouration matches that of their home gorgonian colony. Pygmy seahorses are not found in India, but are present in Indonesian waters. Photos: Dhritiman Mukherjee
Gorgonians (Muricella sp.) and their inhabiting pygmy seahorses can be rather easy to miss if one does not look carefully. Pygmy seahorses are small (less than 2-3 cm in size), and their bodies are covered with warts that resemble gorgonian polyps. Their prehensile tails hold onto gorgonian branches, and like the coral, they too face the current to feed on drifting plankton. Photo: Dhritiman Mukherjee
Seahorses evoke a dreamy view of the marine world. Imaginations come alive with visions of the lost city of Atlantis or the horse carriages operated in the worlds of Aquaman and Ariel. Unfortunately, these dreams die when one hears of the global annual catch of 70 million specimens, often traded by 80 different counrties for their value in Chinese traditional medicine, and aquarium and curio markets. In India, seahorses are a big part of trawler by catch. Unfortunately, their status as Schedule 1 species on the wildlife protection act doesn’t prevent them from getting caught in nets and ground up with trash fish for fish meal and fertiliser. Absurd unscientific beliefs cause seahorses to be used as cures for infertility, baldness, asthma, and arthritis. Photos: Dhritiman Mukherjee (left), Vardhan Patankar (right)
Seahorses are ancient creatures. Their unique shape and behaviour add a layer of mystery. They have voracious appetites and are known to influence marine community dynamics as a result of their feeding activities. Unfortunately, today they are threatened by climate change, overfishing and habitat destruction. Seahorse focused conservation efforts can improve general ecosystem health, given their close association with their surroundings. Photo: Umeed Mistry
is a marine biologist, broadly interested in reproductive ecology, marine larvae and population connectivity, forever fascinated by marine invertebrates
