A cheap and environmentally friendly system for cleaning polluted water should help keep farmed fish free of infections. Michela Magaraggia from the University of Padova, Italy, and colleagues have developed a technique to prevent fungal infections in trout farms. 

Magaraggia's method combines visible light and porphyrin compounds to tackle diseases caused by the Saprolegnia species. When light shines on the porphyrins, they generate oxygen species with a short life span which can affect only their immediate surroundings. The oxygen species attack many cell constituents, ruling out the risk of selecting resistant microbial strains. 

Fish-farmed trout © iStockphotos

Concentrated fish populations, such as those found in fish farms, provide ideal conditions for fungal infections, said Magaraggia. 'Infections in fish eggs represent a heavy financial loss worldwide.' 

The new method could potentially remove an extensive range of pathogens. 'It will eliminate the current practice of using carcinogenic chemicals such as formaldehyde as the main disinfecting agent,' said Gianluca Li Puma, a scientist from the University of Nottingham, UK.

Magaraggia pointed out that the procedure is cheap and potentially safe. 'The accumulation of porphyrins in the environment is unlikely, owing to the gradual photodegradation induced by visible light,' she said.

It could also answer some wider issues for water sanitation, added Magaraggia. 'The procedure can be potentially extended to the treatment of irrigation or drinking water - a major problem in developing countries for the prevention and limitation of diseases.'

Michele Zgraggen