New-to-science seahorse is one of three long-misidentified species

Scientists have identified a new seahorse species, Hippocampus amandavincentae, from the Indian Ocean, based on two specimens collected from trawler bycatch in Tamil Nadu.
The discovery has helped resolve over a century of taxonomic misidentification by revealing that the thorny seahorse, earlier believed to be a single species – Hippocampus histrix, is actually three distinct species.
As indiscriminate fishing and illegal trade threaten seahorse populations, the study’s findings contribute to a clearer picture of spiny seahorse diversity in the Indo-Pacific region.

Scientists have identified a new-to-science seahorse species from the Indian waters, which has helped resolve the taxonomy of a group misidentified for over a century.

In 1856, zoologist Johann Jakob Kaup described the thorny or spiny seahorse, Hippocampus histrix, based on samples from Japan. Since then, this seahorse has been thought to be a single, widespread species ranging from the Red Sea, through the Indian Ocean to Japan, Indonesia and the Pacific Islands.

Over 150 years later, in 2019, a team of researchers collected two seahorse specimens from trawler bycatch that landed at the Thoothukudi Fisheries Harbour in Tamil Nadu. After studying their morphology and genetic data, and comparing them with samples housed in museum collections around the world, the researchers realised that these two specimens represented a distinct lineage.

Their study, published recently in Zootaxa, confirmed what was once thought to be H. histrix is not one, but three separate species—Hippocampus histrix in the Pacific Ocean, Hippocampus jayakari in the Arabian region, and the newly described species from the Indian Ocean named Hippocampus amandavincentae, whose population had long been clubbed with H. histrix.

The findings provide a better understanding of spiny seahorse diversity in the Indo-Pacific region. “This discovery shows that identification and understanding species is the first step towards protecting them and their habitat,” said Shalu Kannan, the study’s lead author and a project scientist at the Zoological Survey of India, Andaman and Nicobar Regional Centre.

New-to-science seahorse is one of three long-misidentified species — The two specimens that led to the description of *Hippocampus amandavincentae* were collected from trawler bycatch at the Thoothukudi Fisheries Harbour in Tamil Nadu. Image by Shalu Kannan.

Not one, but three species

Seahorses belong to the family Syngnathidae which includes pipefishes and seadragons—marine species in which males give birth. Although spiny seahorses are easily recognisable as a group, individual species are harder to distinguish as they can vary in appearance and camouflage themselves based on their environment.

“Misidentification of seahorses has been undertaken by many researchers globally because of limited characters to delineate between species…” said A. Murugan, a seahorse researcher from Tamil Nadu and a member of the IUCN SSC Seahorse, Pipefish and Seadragon Specialist Group. He was not involved in the study.

The taxonomy of H. histrix has proven particularly challenging. A 2016 paper pointed out that this name has been “casually used for virtually any spiny seahorse” in the Indo-Pacific region, suggesting that it may encompass more than one cryptic species. Kannan explained that while integrative taxonomy—which combines multiple types of evidence, including morphology and genetic data, to describe species—is now widely used in India, previously, two species with similar morphology were sometimes given the same name.

The recent study was part of Kannan’s PhD work at Kerala University of Fisheries and Ocean Studies (KUFOS). “I was looking for the previously recorded H. histrix that had been reported from Tamil Nadu,” she said, adding that it took her over a year to obtain the specimens. “Without the fishermen’s help this discovery won’t be possible,” she noted.

The two specimens Kannan brought back to the lab were 16 centimetres long and showed subtle differences from other spiny seahorses. But with such limited samples, it was hard to establish them as a distinct species.

“Describing a seahorse is not easy. You have to compare it with other seahorses of the world. To obtain them, you need access to museum specimens which are outside India,” explained Rajeev Raghavan, the study’s co-author and an assistant professor at the Department of Fisheries Resource Management, KUFOS. Through taxonomist and co-author Graham Short, the team gained access to measurements and genetic data of seahorses from other countries.

A live photograph of the newly described Hippocampus amandavincentae in its natural habitat in Kerala's coastal waters. Image by A. Biju Kumar. — *Hippocampus amandavincentae* in its natural habitat in Kerala’s coastal waters. Image by A. Biju Kumar.

In the case of H. amandavincentae, the main characteristics that separate it from true H. histrix are its shorter snout, five spines on its coronet or crown region instead of four, and stouter spines along its trunk and tail. “When we conducted the molecular analysis, we found that there is a 6-7% difference between the Indian Ocean and the Pacific species,” said Kannan.

The team also studied dive photo records and found genetic data and photographs from Madagascar, Mozambique, and the Seychelles, suggesting the species is more broadly distributed through the Indian Ocean.

They also found a genetic sequence from the northern Red Sea where H. jayakari occurs, leading them to suggest the boundary between H. jayakari and H. amandavincentae needs to be investigated further. Raghavan noted that the “poorly known” H. jayakari has not been recorded in photos or studies since it was first discovered from Oman.

The researchers named the new species after Amanda Vincent, co-founder of Project Seahorse, to honour her work in seahorse research and conservation.

According to Murugan, this discovery is significant and could “promote young researchers and scientists already involved in underwater studies to explore more on fish diversity, with a special focus on seahorses.”

Describing a seahorse isn't easy, say researchers, who had to study other seahorse species and dive photo records of H. amandavincentae from Madagascar, Mozambique, and the Seychelles, aside from the two specimens collected from Tamil Nadu. Image by Daniela De Angelis. — Describing a seahorse isn’t easy, say researchers, who had to study other seahorse species and dive photo records of *H. amandavincentae* from Madagascar, Mozambique, and the Seychelles, aside from the two specimens collected from Tamil Nadu. Image by Daniela De Angelis.

Bycatch pressure

As one of the most threatened groups of fish, seahorses are listed under Schedule I of India’s Wild Life (Protection) Act, 1972, which prohibits their capture, use and trade. Despite this, “there is an extremely strong clandestine illegal trade that happens on the southeast Indian coast,” said Raghavan. Several reports have surfaced of dried seahorses being seized, usually bound for countries where they are used in traditional medicine.

Seahorse populations also face pressure from indiscriminate fishing. A 2020 study found that approximately 13 million seahorses were caught annually between 2015 and 2017 as bycatch in India, mostly by non-selective fishing gear. Raghavan pointed out that their team’s discovery was also based on bycatch specimens, which shows that bottom trawling is catching fish and other marine creatures “that are threatened and possibly undocumented.”

For seahorses caught in drag nets used by bottom trawlers, “the level of survival for undertaking any rescues or catch-oriented release programmes are very much limited,” explained Murugan. He added that the incidental bycatch of seahorses is hard to avoid as they share their habitat with species of commercial value in high demand in international markets, like the blue swimming crab and shrimp.

Murugan believes enforcement alone may not be the solution, and that it needs to be combined with existing aquaculture techniques to conserve seahorses, although he noted that scientific opinion is divided on stock enhancement.

Indiscriminate fishing is a major threat to seahorses, with them frequently turning up as incidental bycatch. Image by Ramvilas Ghosh. — Indiscriminate fishing is a major threat to seahorses, with them frequently turning up as incidental bycatch, along with many other species. Image by Ramvilas Ghosh.

Future roadmap

At present, population information for H. amandavincentae remains unknown, but the study provides a clearer picture of its range. “This is possibly the only species of seahorse that is endemic to the Indian Ocean,” said Raghavan. He added that its distribution coincides with major marine fishing regions such as the Bay of Bengal and the Arabian Sea, “which means if bottom trawling and marine bycatch are not regulated, there are chances this species would be extremely highly threatened.”

Researchers say the conservation status of H. histrix—classified as Vulnerable in the IUCN Red List — will need to be reassessed based on its revised range. “Now, we have demarcated a distribution boundary for H. histrix, saying it’s the Pacific species until possibly Malaysia or Thailand, and anything west of that region is the Indian species,” explained Raghavan.

Specimens of the Indian Ocean species deposited in museum collections will also have to be re-examined since they have long been misidentified as H. histrix, the authors say.

With the new description, seven seahorse species are now known from Indian waters. “While seahorses have been recorded from both coasts (east and west), the Tamil Nadu coast (east) is more diverse, observed Kannan. Underwater studies are needed to learn about their habitat and population, she noted, adding, “I think there are more undiscovered species in this region. More studies are required to explore and discover species from the Indian Ocean.”

Banner image: Hippocampus amandavincentae is thought to be endemic to the Indian Ocean. Image by Daniela De Angelis.