4.5.3.2 Natural plant extracts

Background

One of the sub-objectives of the Aquaculture centre was to experiment in finding ecological solutions for fish disease treatment.

In the summer of 1995 an outbreak of white spot disease occurred caused by a skin parasite called Ichthyophthirius multifiliis.

This ciliated protozoan can be just seen by the naked human eye as a white dot or spot on the fish's skin.

It's life cycle begins by a juvenile hitching a ride on a host fish and once attached to the scales or gills, begin to take hold on the surface and in quantity will irritate the fish, which can be seen to dart about and scrape itself against rocks to ease the itching (hence it's other common name - 'itch' ! ). The adult parasite will finally release hundreds of tiny replicas of itself and die, leaving the young to begin the 11 day cycle again.

Like a human common cold, if the problem remains unchecked it can develop to a more serious condition and can result in death. In nature, the protozoan will only damaged stressed, ill or weak specimens and other invertebrate predators will keep 'itch' to controllable populations.

However, in captivity the invertebrate balance is disturbed and white spot populations can become rife. Current conventional cures involve dosing with chemicals namely the clothing dyes of Methylene blue and Malachite Green, both known carcinogens to humans. The treatment can not only stress the fish further but can have devastating effects on localised aquatic wildlife if the residue is not disposed of correctly.

An eco-alternative

After trying several plant extracts our on-site 'organic' gardeners suggested we try rhubarb leaves:

Rhubarb Rheum rhubarbarum

originates from North-West China & Tibet by the Renaissance era reaching Europe and has been used for medicinal purposes for the past 2,000 years.

Normally, only the stems and root are consumed as the leaves are known to be toxic with anti-bacterial oxalates found in large quantities.

leaves were steeped in a 5 litres of cold water and applied in liberal quantities to the tanks.

To our amazement after about 24 hours the characteristic grey-white skin smears began to diminish and after a few days the fish where behaving normally again. This was even successful in treating Stickleback's whom are know to endemically carry the disease in large colonies.

Later, we scrutinized the 'treated' protozoans under the microscope and found that the rhubarb extract had congealed around the cilia of the invertebrate and effectively immobilised the creature. This in turn, halted final stage development and broke the reproductive cycle.

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