Tiny fish louse shows promise as a sensitive early indicator of metal pollution in freshwater
By Edsel Cook // Nov 15, 2018

A common aquatic parasite might one day inform us about the presence of dangerous metals in drinking water. The fish louse (Argulus japonicus) is being tested as a biological early warning system for water quality, an article in Science Daily stated.


Agricultural, industrial, and urban activities produce harmful chemicals and substances that can contaminate drinking water sources. Metal pollutants are the most insidious of the lot due to the difficulty in detecting their presence.

A water sample is limited to telling you about the state of the water during the time of its taking. A fish can accrue toxins over a period of time, but it also moves those pollutants to a safer part of its body, making them harder to find.

University of Johannesburg (UJ) researcher Annemariè Avenant-Oldewage suggested studying parasites found in fish. A parasite absorbs large amounts of the metals from its host, making the pollutants much easier to detect.

"This means we can measure metals in them, long before it is possible to do that in fish or in water samples," remarked Avenant-Oldewage. "So parasites can give us early warnings of pollution." (Related: Fruit and vegetable peels can be used to remove water pollutants.)

A parasitical crustacean can warn you about toxins in drinking water

Initial candidates included the tapeworm and the monogean Paradiplozoon. The former is an internal parasite that required its host fish to be killed, while the latter is an external critter that targets only two species of yellowfish.

The UJ researchers settled on the fish louse. A distant relation of shrimps that can thrive in both freshwater and saltwater, it swims in search of a host, latches onto the skin of the fish, and drinks the blood of its victim.

Unlike Paradiplozoon, which is attached to the gills of the yellowfish, a  fish louse can be removed from its host without harming the fish. These qualities make it perfect for testing water pollution levels

UJ researcher Beric Gilbert caught mudfish and yellowfish in the Vaal Dam near Deneysville, South Africa. He removed Argulus from those fish, froze the crustaceans, added fluorescent stains, and examined the fish lice with a special microscope.

Underneath the microscope, the metal pollutants would glow yellow. The higher the amount of such toxins, the more intense the fluorescent signal.

Fish lice used to test metal pollutant levels in water

Gilbert reported that the metal pollutants were concentrated in the tough exoskeleton of the fish lice. Male and female Argulus specimens absorbed roughly the same amount of the toxins. However, they stored it in different parts of their bodies according to their sex. In male fish lice, the metals were concentrated in the bottom part of their bodies.

For female lice that carried eggs, the pollutants were present in the jelly layer that surrounded their future offspring. This jelly is very sticky, and it is used by the female to glue its eggs to the surface of various objects in its habitat.

Avenant-Oldewage stressed the need for further experimentation with the fish lice before the animals can be considered accurate and reliable indications.

"Our next step is to find out what mechanisms the lice use to protect themselves from metals," she explained. "We also need to find out how they absorb metals in the first place."

Still, the UJ professor has high hopes for the little critters. If they pass muster, fish lice could become a new tool in the arsenal of water quality inspectors, helping to ensure that our drinking water is truly safe.

Worried about the safety of your local water supply? Visit CleanWater.news to find out if you are in the clear.

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