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Helping the mangrove clam spawn

Junelyn S. de la Rosa

Imbao or the mangrove clam

With the destruction and overexploitation of mangroves that serve as its home, the mangrove clam (Anodontia edentula) or imbao has been declining in numbers. To solve this problem, a group of scientists from Southeast Asian Fisheries Development Center (SEAFDEC), Tigbauan, Ilo-ilo studied various techniques to help imbao spawn.

Among the techniques studied, the use of serotonin was the most successful at the rate of 94.38% successful spawns.

The mangrove clam

Belonging to the family Lucinidae, the mangrove clam buries itself in the mud of mangrove areas or in the adjacent mudflats. It grows to a maximum size of 8-9 cm shell length at 180-210 grams. It has an elongated adductor muscle, part of which is separate from the pallial line. The hinge is essentially toothless in the adult, hence it is also called the toothless clam.

The mangrove clam is a very interesting animal. It has sulphur-oxidizing bacteria in its gills from which it derives most of its nutrition. Because of this special ability, the mangrove clam and other lucinids have, therefore, lost their siphons and their ability to filter feed, and make connection with the outside world with their piston-like feet.

This clam is widely distributed in the Indo-West Pacific and in the Philippines. It can be found mostly in the Visayas and Mindanao where it is an important food and source of livelihood for many farmers. One of the popular shellfishes in the Philippines, the mangrove clam or imbao makes a delicious soup or grilled and is prized a little more than other shells at P5 to P8 per piece.

Inducing them to spawn

In the study by SEAFDEC, mangrove clams were collected from mangroves in San Roque, Estancia, Iloilo and Mambuquia, Sapian, Capiz using the "mata "system a non-destructive collection method. The researchers hired the services of skilled imbao collectors, people who can pinpoint the exact location of imbao through the opening of its siphon, or what is locally called "mata " (a reference to the hole or opening in the substrate). This method spares mangroves from damage caused by digging.

After cleaning the clams using a soft brush to get rid of mud and other debris, they were measured for shell length, width, and height using a Microstat caliper.

A biopsy was conducted to determine sex and the quality and quantity of gametes in stalked eggs or active/motile sperms. Mangrove clams are dioecious which means that while the sexes are separate these are not differentiated externally, hence the need for the biopsy.

Among the spawning techniques using chemicals such as hydrogen peroxide, ammonium hydroxide, serotonin, and temperature shock, the use of serotonin was the most successful with 94.38% successful spawns. Moreover, female and male adults were successfully induced to spawn using serotonin. Females that spawned ranged from 60 g, 57 mm shell length to 125 g, 73 mm shell length. The maximum number of eggs spawned by a 71 g female was one million.

A new potential discovered

In another experiment, researchers from SEAFDEC are also studying the potential of mangrove clams to clean-up sediments and make polluted waters habitable again. The mangrove clam harbors symbiotic bacteria in its gills. This kind of bacteria can oxidize sulfur thereby cleaning the water of sulfur in the process.

Today, the scientists are looking into the potential of the mangrove clam as a sediment cleaner and the feasibility of its being raised in polyculture with shrimp. It is a fact that brackishwater pond sediments contain plenty of sulfide, particularly where cultured animals are fed protein-rich diets. Scientists are optimistic that the in the near future, the mangrove clam will not only continue to delight many a Filipino palate but can be used as an effective helper in cleaning our ponds and sustaining an environment-friendly aquaculture.

"Induced spawning and larval development of the mangrove clam, Anodontia Edentula" Ma. Junemie Hazel Lebata, Jurgenne Primavera, Jon Altamirano, Ellen Flor Doyola and Liliane Gustilo of Southeast Asian Fisheries Development Center (SEAFDEC), Aquaculture Department, Tigbauan Ilo-ilo