Industrial processing of fish yields approximately 60% waste (Raa and Gildberg, 1982). Fish waste is a valuable source of proteins and lipids that can be used for human and animal nutrition. These by-products can be upgraded in a cheap, environment friendly way by fermentation with lactic acid bac-teria (LAB), after adding a fermentable carbohydrate (Raa and Gildberg, 1982). Due to acidification and enzymatic activities, LAB can play a considerable role in improving the organoleptic, hygienic and nutritional quality of fish by-products (Raa and Gildberg, 1982). Further research is needed to ensure that this promising preservation method will yield safe, high quality products. Ensiled fish contains a considerable amount of the free amino acids that constitute the precursors for biogenic amines such as histamine, tyramine, putres-cine and cadaverine (Haard et al., 1985). Biogenic amines are formed by decarboxylation of their precursor amino acids, as a result of the action of
either endogenous amino acid decarboxylase activity (Halasz et al., 1994) or by the growth of decarbox-ylase positive microorganisms (Halasz et al., 1994; Silla Santos, 1996). The low pH (below 4.5 after 2 days of fermentation) and the physical characteristics of fish silage that lead to a low oxygen concentration within the ensiled fish are favourable for the action
of amino acid decarboxylases (Beutling, 1992). Thus, biogenic amines may pose a potential risk in fish silage. These compounds are toxic for livestock, causing liver damage and decreasing the perform-ance of the animals (Krizek, 1991). In susceptible humans, they can lead to a variety of cutaneous,gastrointestinal, haemodynamic and neurological symptoms (Taylor, 1986).Biogenic amines can be degraded by amine oxid-ases. Diamines, such as histamine and putrescine, are degraded by diamine oxidase (DAO). The activity of these enzymes is maximum under neutral to alkaline conditions, and oxygen is necessary for their action (Beutling, 1992). DAO can provide a means of controlling histamine accumulation during the first
days of ensilage, while the pH is high enough and some oxygen is still available within the product.Little is known about histamine degradation by LAB,but Voigt and Eitenmiller (1978) and Leuschner et
al. (1998) found DAO activity among some dairy
and meat isolates, respectively.