Lysozyme plays an important role in the non-specific immune response. Its specific action is to attack the peptidoglycan layer of bacterial cell walls, by hydrolysis of N-acetylmuramic acid and N-acetylglucosamine, resulting in bacterial cell lysis. It has been found in mucus, serum and ova of fish [1,2].
There appears to be variants of lysozyme in fish (types I and II) and type I appears to be significantly more reactive than the lysozyme found in mammals in that it is capable of attacking Gram-negative bacterial fish pathogens [3].
Mammalian lysozyme usually requires complement to disrupt the outer cell wall of Gram-negative bacteria to allow access to the peptidoglycan layer [4].
Atlantic halibut (Hippoglossus hippoglossus L.) have previously been shown to possess this important defensive protein [5,6]. We have previously studied another non-specific immune factor in halibut, a2- macroglobulin, and showed that this species seems to possess high levels of this protein in the blood [7]. Atlantic halibut appear to have a relatively high level of resistance to both typical and atypical Aeromonas