IPN studies seahorses for their conservation

Zenaida Alzaga

Researchers at the Centro Interdisciplinario de Ciencias Marinas (CICIMAR), part of the Instituto Politécnico Nacional (IPN), are investigating the biology, physiology, and behavior of Pacific seahorses (Hippocampus ingens) for their management and protection in our country.

In Mexico, there are four species of seahorses, three in the Gulf of Mexico and the Caribbean Sea (Hippocampus reidi, Hippocampus zosterae, and Hippocampus erectus), while only Hippocampus ingens inhabit the Pacific.

The Pacific seahorse is distributed from California, United States, to Peru, while specimens found in the Gulf of Mexico and the Caribbean Sea range from the coasts of Florida, United States, to Brazil.

Seahorses are highly demanded species for ornamental use and in traditional Chinese medicine, a situation that has negatively impacted populations worldwide due to increasing overexploitation, bycatch, and habitat destruction.

Currently, 47 species of seahorses are recognized worldwide, and although all of them have been listed as vulnerable on the International Union for Conservation of Nature Red List, two are globally endangered.

The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) added all types of seahorses to Appendix II, marking a milestone as they became the first group of fishes to be included in this appendix, thus providing a means to monitor and regulate the trade of these species internationally.

Dr. Renato Peña Martínez, a researcher at the Mariculture Pilot Unit of CICIMAR, indicated that in Mexico, the Official Mexican Standard NOM-059-SEMARNAT-2010 establishes the "Environmental protection of native species of Mexico of wild flora and fauna that are at risk," and has classified all four categories of seahorses present in Mexico as species subject to special protection (Pr).

He added that through the "Seahorse Project," basic and applied knowledge about seahorses will be generated since there is little information about their biology and development, allowing for the implementation of management and conservation plans to counteract seahorse exploitation.

Experts work in the Bay of La Paz, in the Gulf of California, where they have captured breeding specimens of Hippocampus ingens (with the necessary permits from authorities) for reproduction in the laboratory, where cultivation systems have been developed for this purpose.

Currently, there is a batch of breeders measuring 20 centimeters kept in captivity under conditions similar to their habitat, fed with live and frozen food, and so far, they have achieved a one hundred percent survival rate.

Pacific seahorses are found near coastal areas in shallow waters; they are not good swimmers because they lack an anal fin to propel them. They have a sedentary lifestyle, spending most of their time clinging to reefs or macroalgae by their prehensile tail and feeding on small crustaceans such as copepods, amphipods, and mysids, among others.

They lack teeth and a tongue, only sucking food through their tubular snout; they also lack a stomach, so extracted food passes directly from the esophagus to the intestine, which is long and has three well-defined segments, increasing food transit time, favoring digestion and absorption.

The researcher detailed that, in this species, like other seahorses, the male takes care of incubating the eggs and subsequently giving birth to the offspring. The reproductive process begins when the female chooses a mate and initiates a courtship process where both grasp each other's tail and rub the sides of their bodies while changing color; eventually, the female and male bring their bellies together and swim in the water column from top to bottom, circling.

He explained that during this process, the female passes the oocytes to the male's brood pouch, and then he fertilizes them to incubate. After a gestation period lasting about three weeks, the male's pouch swells, and he assumes an upright posture in the water column and, through a series of contractions, begins to expel the offspring (which are born in the form of seahorses); usually, the process occurs in the early hours of sunlight.

He noted that males expel around two thousand offspring, but the mortality rate is very high because they surface to take air to fill their gas bladder, although sometimes they inhale too much air and cannot expel it, preventing them from returning to the water column and causing them to float on the surface, thus dying of starvation. This condition is known as "bubble disease," which is the main cause of death for newly born seahorses.

Dr. Peña pointed out that in the laboratory, a cultivation system is being implemented to reduce the incidence of bubble disease by modifying water flow and temperature, which could reduce the mortality rate.

He indicated that at birth, seahorses have a total length of seven to eight millimeters, and although they already have a seahorse body shape, the body proportions are different from adults.

"Seahorses are animals that live in very low population densities, are solitary, and their sedentary lifestyle makes it difficult for them to find a mate; they reproduce when they reach maturity, which they achieve around eight months of age," he detailed.

He reported that adult males, on average, grow between 28 and 31 centimeters, weigh around 30 grams when not incubating the eggs, and live approximately seven years. "Thanks to their independently moving eyes, they have a wide field of vision that allows them to find food and detect predators," he added.

The researcher emphasized that Pacific seahorses are in the middle of the food chain, but demand from Chinese fisheries has endangered them, as they are dried, ground, and used in Oriental medicine to treat ailments such as asthma and erectile dysfunction, among others.

Therefore, through the "Seahorse Project," research is being conducted as part of different undergraduate, master's, and doctoral theses aimed at generating knowledge to implement conservation policies on the species.

Collaborations have been established with other academic institutions such as the Autonomous University of Baja California, the National Autonomous University of Mexico (UNAM), and the Northwest Biological Research Center, with whom research projects are being conducted in areas of physiology, biology, and seahorse behavior.

Finally, the expert invited students and interested collaborators to study and learn more about seahorses on their website www.facebook.com/SeahorseProject."

Selección Gaceta Politécnica #171. (February 29th, 2024). IPN Imagen Institucional: Read the full magazine in Spanish here.