Not all parasites are harmful. Species of the thorny-headed worm, or acanthocephala (Acanthogyrus species), can infect fishes but they bring more good than harm—on humans.
This was found in a recent study by the Institute of Biological Sciences of the University of the Philippines Los Baños (UPLB) on thorny-head worms—fish-parasites that accumulate heavy-metal concentration in their host’s tissues, such as on gills and intestines.
The study found that fishes infected with parasites (parasitized) have lower levels of heavy-metals, compared with fishes not infected by parasites (non parasitized).
The difference in the tissues of the parasitized and nonparasitized fish is “remarkable,” according to the study.
Thorny-headed worm infection, the study said, affects only the host’s or fish’s size or weight and length but has no significant effect on the immediate health of the fish.
Dr. Vachel Gay V. Paller, National Research Council of the Philippines (NRCP) biologist/researcher, said 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.”
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.
Thorny-headed worms were found in the following four species of fishes: tilapia (Oreochromis niloticus), red nile tilapia, Parachromis Managuensis and Vieja species The highest rate of infection and intensity was recorded in Palakpakin Lake.
Among the 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, wherein the 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 agricultural application in the nearby areas.
The study, funded by the NRCP of the Department of Science and Technology, is relevant at this time when the government is pushing for a cleaner environment, especially in the coastal areas, where many people live and obtain their livelihood.
NRCP will be hosting the Science and Policy Forum for Sustainable Laguna Lake Management on November 22 and 23 in Days Hotel, Tagaytay. The forum will be a gathering of fishers, farmers, environmental experts in the academic, administrative and legislative sectors.