Immune responses of nile tilapia (Oreochromis niloticus L.) clones: I. Non-specific responses

The importance of genetic variation in the non-specific immune responses of Nile tilapia (Oreochromis niloticus L.) clones was investigated. Fully inb red clones (IC) of Nile tilapia, produced using gynogenesis and sex reversa l, and crosses between these lines (outbred clones) were used in this study . Non-specific immune responses were compared between the ICs, including se rum lysozyme activity and phagocytosis, and significant differences were ob served between the different groups. Their natural resistance to Aeromonas hydrophila infection was also assessed by bacterial challenge. A positive c orrelation was observed between the level of infection obtained and the non specific immune parameters measured. Cumulative mortalities of fish obtaine d in the study showed that when a IC susceptible to A. hydrophila was cross ed with a resistant IC, the resulting progeny exhibited intermediate levels of resistance to that of their parents. (C) 2000 Elsevier Science Ltd. All rights reserved.