In San Pablo lakes, metal intake curbed by worms

MANILA, Philippines – A University of the Philippines-Los Baños (UPLB) study on a species of worms in the seven lakes of San Pablo, Laguna found that they prevent intake of heavy metals by fish and may also do the same for humans.

The study conducted by UPLB’s Institute of Biological Sciences and funded by the Department of Science and Technology’s National Research Council of the Philippines (DOST-NRCP), found that the species of Acanthocephala (Acanthogyrus sp.) also known as thorny-headed worm, can infect fish but help, more than harm, the host-fish.

The thorny-headed worms are fish parasites that accumulate heavy metal concentration in their host’s tissues such as the gills and intestine. 

The study found that fishes infected with parasites (parasitized) have lower levels of heavy metal compared with fishes not infected by parasites (non-parasitized).

The difference in the tissues of the parasitized and non-parasitized fish is “remarkable,” according to the study.

Acanthocephalan infection affects only the host-fish’s size or weight and length but has no significant effect on the its immediate health. 

Vachel Gay Paller, NRCP biologist/researcher, says that as the number of parasites increases, the length of tilapia decreases. 

“Smaller tilapia may not be so bad. Some may have parasites, but these parasites may just save the consumers from possible heavy metal intake. Besides, the parasites stay in those parts – gills and intestine – which the consumers most likely discard,” the researcher said.

Conducted in the seven lakes of San Pablo, Laguna – Bunot, Calibato, Mohicap, Palakpakin, Pandin, Sampaloc and Yambo – the study aims to help farmers understand and control the Acanthocephalan infection among fishes in the lakes.

Acanthogyrus sp. were found in the fish species at the lake namely O. niloticus (Tilapia), P. Managuensis, Vieja sp., and Red Nile Tilapia. 

The highest rate of Acanthocephalan infection and intensity was recorded in Palakpakin Lake. 

Heavy metal sources of pollutants in the seven lakes come from transportation vehicle (car exhaust, worn tires, engine parts, brake parts, rust or used antifreeze); and fish cages where uneaten feeds that contain essential minerals for fish diet (copper, calcium, zinc, selenium, magnesium, potassium, phosphorous, manganese, iron and iodine) accumulate in the lake over the years. 

Other sources include untreated wastes from hospital, residential, commercial and industrial establishments; and pesticides from nearby farms.