An efficient clearance and degradation system may be needed during microbial invasion which otherwise would lead to severe inflammation and eventually death. Non‐specific defence mechanisms in fish play an important role at all stages in infection. The non‐specific humoral defence including proteases, lysins and agglutinins, for example, in mucosal secretion is the first line of defence, whereas mucosal lining cells function as the second barrier against invasion. Blood cells, especially granulocytes and monocytes, may destroy microbes present in the circulation and may function as the third line of defence. Finally, endocytically active cells such as endothelial cells, macrophages and granulocytes in organs and tissues may take up and degrade microbes or microbial products. The endocytic and degradation processes strongly depend on the effectiveness of the reticuloendothelial system which consists of endothelial cells and macrophages that line small blood vessels (e.g. sinusoids and ellipsoids). Potentiation of non‐specific defence mechanisms may occur during microbial invasion, leading to more efficient clearance and destruction of pathogens or other harmful substances. In microbial invasion, an inflammatory response such as elevated production of antimicrobial substances is often encountered. Central cells in the production of antimicrobial substances are macrophages and granulocytes, and microbial products in inflammation may alter the cells function to a more activated state in vivo. Activated cells may enhance their antimicrobial capacity and efficiency by producing higher amounts and more active antimicrobial agents. This review concerns the non‐specific defence system and gives an introduction to some of the known non‐specific humoral substances and their induction/suppression, and provides a more extensive introduction to cytokine research and immunomodulation. Cellular aspects of non‐specific defence, including macrophages and their products, are discussed in the light of their function in the reticuloendothelial system in fish.

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The aims of this study were to investigate the content of emamectin in blood, mucus and muscle following field administration of the recommended dose, and correlation with sea lice infection on the same fish (elimination study). The tissue distribution of tritiated emamectin benzoate after a single oral dose in Atlantic salmon was also investigated by means of whole-body autoradiography and scintillation counting (distribution study). In the elimination study, concentrations of emamectin benzoate reached maximum levels of 128, 105 and 68 ng/g (p.p.b.) for blood, mucus and muscle respectively, on day 7, the last day of administration. From day 7, the concentration in the blood declined until concentration was less than the limit of detection on day 77. The concentration was higher in mucus compared with plasma (P < 0.05) except on days 7 and 21. The concentration of emamectin benzoate decreased gradually from the end of treatment (day 7) to day 70 with half-lives of 9.2, 10.0 and 11.3 days in muscle, plasma and mucus respectively. The distribution study demonstrated a high quantity of radioactivity in mucous membranes (gastrointestinal tract, gills) throughout the observation period (56 days). Activity was high in the epiphysis, hypophysis and olfactory rosette throughout the study. The highest activity was observed in the bile, indicating this to be an important route for excretion. The distribution study confirmed the results from the elimination study with respect to concentrations in blood, skin mucous and muscle.

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Waller PJ, Bernes G, Thamsborg SM, Sukura A, Richter SH, Ingebrigtsen K, Höglund J: Plants as deworming agents of livestock in the Nordic Countries: historical perspective, popular beliefs and prospects for the future. Acta vet. Scand. 2001, 42, 31-44. -Preparations derived from plants were the original therapeutic interventions used by man to control diseases (including parasites), both within humans and livestock. Development of herbal products depended upon local botanical flora with the result that different remedies tended to develop in different parts of the world. Nevertheless, in some instances, the same or related plants were used over wide geographic regions, which also was the result of communication and/or the importation of plant material of high repute. Thus, the Nordic countries have an ancient, rich and diverse history of plant derived anthelmintic medications for human and animal use. Although some of the more commonly used herbal de-wormers were derived from imported plants, or their products, many are from endemic plants or those that thrive in the Scandinavian environment. With the advent of the modern chemotherapeutic era, and the discovery, development and marketing of a seemingly unlimited variety of highly efficacious, safe synthetic chemicals with very wide spectra of activities, herbal remedies virtually disappeared from the consciousness -at least in the Western world. This attitude is now rapidly changing. There is a widespread resurgence in natural product medication, driven by major threats posed by multi-resistant pest, or disease, organisms and the diminishing public perceptions that synthetic chemicals are the panacea to health and disease control. This review attempts to provide a comprehensive account of the depth of historical Nordic information available on herbal de-wormers, with emphasis on livestock and to provide some insights on potentially rewarding areas of "re-discovery" and scientific evaluation in this field. plant anthelmintics; herbal remedies; helminth parasites; livestock; man.