Mitigation of red mark syndrome in rainbow trout with functional diets (39829/103446)

Red mark syndrome (RMS) is a skin disease affecting rainbow trout under farming conditions. The disease is not associated with any recognizable mortality, but results in economic losses on behalf of the fish farmer as fish are often affected around the time of sale, and the unappealing appearance has implications such as costs for sorting, down-grading, management challenges or costumer dissatisfaction.

The large skin lesions appear to be caused by an overreaction to a poorly characterized bacterium in the family Midichloriaceae within the Rickettsiales order. This bacterium is provisionally called Midichloria-like organism (MLO).

The only current way of treating RMS is with antibiotics. However, as antibiotics cannot be used prophylactically, and RMS cannot presently be diagnosed before lesions appear, the practical use is relatively limited, since lesions spontaneously heal anyway. There is a positive effect on the part of the pond that do not yet have symptoms (metaphylaxis), but this benefit is somewhat offset by the necessary antibiotics withdrawal period.

It is hypothesized that the immune response towards MLO can be modulated through functional feeds and/or that the healing phase is improved. The disease is apparently not associated with loss of appetite, or at least to a limited extent. Thus, functional feeds can potentially be administered before as well as during an outbreak.

In this project two experimental feeds are tested against a control feed. The experimental fish are exposed to RMS and the development of visual disease, MLO load and immune response is followed over the course of lesion development and healing.

Partners
National Institute of Aquatic Resources (DTU Aqua), Technical University of Denmark
BioMar A/S, Norway

Funding
The project is funded by BioMar A/S. 

Research area: Fish and Shellfish Diseases