Studies on acanthocephalans feature many aspects of parasite biology. These parasites are known to play important roles in shaping ecosystems through regulation of their hosts’ population structure. Studies have also shown both their potential as agents of disease upon reaching epizootic levels and biomonitors of anthropogenic disturbances. Hence, this research was conducted to identify the acanthocephalan fauna of the Philippine freshwater fishes and to generate baseline information on their infection dynamics in their fish hosts. It also aimed to determine the pathogenicity of acanthocephalans in their fish hosts as well as their efficiency as bioindicators of heavy metal pollution in aquatic ecosystems. Fishes were collected in the wild from Seven Lakes of San Pablo Laguna namely; Bunot, Calibato, Mohicap, Palakpakin, Pandin, Sampaloc, and Yambo Lake, from February 2013 – March 2015. Freshwater fishes include Carassius carassius (Crucian carp), Channa striata (Snakehead murrel), Cyprinus carpio (Common carp), Giuris margaritacea (Snakehead gudgeon), Glossogobius giuris (White goby), Leiopotherapon plumbeus (Tiger perch), Oreochromis niloticus (Nile tilapia), Parachromis managuensis (Jaguar guapote), Red Nile tilapia, and Vieja sp. (Flowerhorn). Species of Acanthocephala namely Acanthogyrus sp. was found in all the lakes. It was found to frequently infect O. niloticus, P. managuensis, Vieja sp. and Red Nile tilapia all belonging to F. Cichlidae. Highest infection rate of Acanthogyrus sp. in O. niloticus was recorded in Palakpakin, followed by Sampaloc, Pandin, Yambo, Mohicap, Bunot, and Calibato Lake with prevalence values of 79.4%, 73.0%, 71.5%, 51.1%, 50.9%, 48.7% and 31.3%, respectively. The overall mean intensity was four parasites per fish in the Seven Lakes, with Palakpakin showing the highest (9 parasites per fish), and Calibato Lake as the lowest (1 parasite per fish). Furthermore, observed prevalence was higher during dry season (56.6%) than wet season (55.0%). Similar trend was observed on the mean intensity with value of 5.0 ± 3.0 and 3.0 ± 1.0 during dry and wet season, respectively. The potential use of acanthocephalan parasites as heavy metal bioindicator in aquatic ecosystem was investigated. Parasitized fish accumulated lower lead (Pb) concentration (7.64 mg/kg) than in the uninfected fish (21.87 mg/kg). Parasites recovered from the infected fish accumulated higher Pb concentrations (10.13 mg/kg) than the fish liver (6.19 mg/kg), intestine (2.80 mg/kg), and muscle (0.75 mg/kg). Also, parasites showed Pb bioaccumulation capacity which was 3015 times higher than the established bivalve bioindicator, Corbicula fluminea. The uptake of Pb by acanthocephalan, Acanthogyrus sp. is clearly beneficial to its host and is therefore valuable as environmental indicators, particularly for assessing aquatic heavy metal pollution. Further analyses were conducted to evaluate the effect of the parasites on the general health of its hosts. Hematological and histological manifestations of the parasitized fish were evident but revealed no severe effect on the overall health of its fish hosts. Likewise, pattern of distribution of the parasites infecting the fish host population was found to be highly aggregated (D=0.73) which implies that a general healthy fish populations is maintained. However, superinfections in the host could cause serious epizootics particularly during an adverse condition in the environment. This study could serve as baseline information for future investigation on acanthocephalans and their role in shaping ecosystems in the Philippines. In addition, this study demonstrates the emerging potential use of parasites as monitors of environmental quality implying a novel role as sentinels of metal pollution in aquatic ecosystem.