Marine Parasites as Bioindicators for Toxins and Their Potential Role as Environmental Sinks for Marine Fauna.

Background: Researches are being frequently conducted on the utility aspects of helminth parasites worldwide. The evolution is driven by the need for survival against the toxicity of biometals that emerged in zoonotic roundworms of Anisakidae.

Aims: This study is aimed at investigating whether the sequestration of biometals from the environment into the body tissues of parasites serves a dual purpose: firstly, the removal of toxic metals and other biotoxins from the immediate environment of worms and, secondly, the utilization of extra available biometals, like sulfur and cysteine, in the surrounding environment to strengthen the cuticularization for the body's defense. Additionally, it examines whether the toxins absorbed by the tissues of worms thus protect tissues of the fish host from damage caused by toxicity; the potential "environmental sink" thus came into operation.

Methods: These worms exploited the alterations in chemical composition to adapt and evolve in the newer environment. An assessment of biotoxic influence generated through heavy metal toxicity was conducted during this investigation. Scanning electron microscopy and energy-dispersive x-ray micrographic analysis were the techniques employed. The studies were conducted in anisakid nematodes parasitizing reef-associated fishes at Ilha "Grande" Island, 19 km from Panaji, Goa, in India.

Results: The first record of Anisakis typica third-stage larvae has recently appeared in Indian fish. The survival of worms of Anisakidae under the influence of a hostile environment comprising toxic biometals, like Hg, Pb, and Cd, was analyzed. The hypothesis of the metal filter being functional at the worm-iron influx interface was propounded. The typical anisakids of the family Anisakidae trigger a zoonotic mechanism that involves damage to human health.

Conclusions: The superfluous iron influx within the intestinal environment apparently brought about physiological changes in the host's body tissues as well. The excessive iron content from the tissues of nematodes first crossed the worm's membrane barrier. Next, the iron content was stored in different body organs of roundworms to avoid the influence of toxicity on the fish host's body. Apparently, the parasitic tissues of the nematode functionally operated as an environmental sink which could relieve body tissues of the host fish due to unwarranted duress under biometallic stress.