SARF001: Prevention & management of Ichthyophthirius multifiliis

Start Date: 01/02/2005
End Date: 31/08/2005
Main Contractor(s): Institute of Aquaculture, University of Stirling
Other Sponsor(s): Defra

Objectives

Scientific objectives of the SARF project. The main objective of the project is to test the efficacy of three novel mechanisms for the control of I. multifiliis in trout farms by first of all conducting laboratory trials to optimise their use before assessing their performance under field test conditions. Specifically, the project objectives are as follows:

  1. Build and test the mechanical modular system at the Institute of Aquaculture and test its efficacy in killing the different stages of laboratory reared populations of I. multifiliis. The construction of a scale model concrete raceway at Stirling on which to test the modular system will be necessary.
  2. Install the mechanical system within the hatchery unit of a working farm site with a history of I. multifiliis and assess its action over the summer period when the likelihood an outbreak is high.
  3. Optimise the chemical constituents of the "raceway treatment" and conduct laboratory and field trials to assess its action on different stages of the parasite's life-cycle. Trials will define the activity of the treatment (duration and efficacy of the anti-protozoal action) under differing environmental conditions.
  4. Conduct field and laboratory trials with the novel in-feed nutriceutical to establish an effective dose and regime for its use.

Summary

The ciliate protozoan Ichthyophthirius multifiliis or whitespot disease is recognised to be one of the most pathogenic diseases of wild and cultured freshwater fish. Mortalities result when large numbers of the mature parasitic trophont stage exit the host causing disruption to the epidermis and interfere with the osmotic balance of the host. Ichthyophthirius multifiliis now represents the number one parasite problem for the UK trout industry and accounts for an estimated 2-5% loss in production amounting to £2 million in lost revenue. The EU ban on the use of malachite green and dimetradizole as efficacious treatments in food fish, has left the industry without suitable replacements for the treatment of I. multifiliis. The objectives of the project are, therefore, to test the efficacy of three novel approaches to control and treat outbreaks of I. multifiliis in rainbow trout farms. Specifically, the project will construct and test a mechanical device under laboratory and field conditions that kills and removes tomonts and cysts from raceways thereby preventing the proliferation of the parasite within systems. Several formulations of a long-duration raceway treatment will be tested in its ability to prevent parasite settlement and encystment. Inhibition of encystment will break the parasite life-cycle by preventing binary fission of the parasite and the release of infective stages. The third approach will test the action of an in-feed nutriceutical in reducing the number of trophonts surviving on fish receiving a regime of medicated diet. The benefits of these approaches to treating I. multifiliis are long-term protection of farm stock, lower levels of infection and therefore an improvement in the health and welfare of fish, and reduced chemical use. The relevance and the approach of the proposed project falls within SARF's mission statements to fund research into protecting the health and welfare of aquaculture stocks by developing strategies to minimise the impact of parasitic disease upon them.