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 inbred clones (IC) of Nile tilapia, produced using gynogenesis and sex reversal, and crosses between these lines (outbred clones) were used in this study. Non-specific immune responses were compared between the ICs, including serum lysozyme activity and phagocytosis, and significant differences were observed between the different groups. Their natural resistance to Aeromonas hydrophila infection was also assessed by bacterial challenge. A positive correlation was observed between the level of infection obtained and the non-specific immune parameters measured. Cumulative mortalities of fish obtained in the study showed that when a IC susceptible to A. hydrophila was crossed with a resistant IC, the resulting progeny exhibited intermediate levels of resistance to that of their parents.

Production and propagation of fully inbred clonal lines in the Nile tilapia (Oreochromis niloticus L.).

Fully inbred clonal lines of fish are likely to be of great value in research on immunology, sex determination, quantitative genetics, and toxicology. In this study on the Nile tilapia (Oreochromis niloticus), gynogenesis or androgenesis were used to produce a first generation of completely inbred fish, from which clonal lines were established using gynogenesis, androgenesis, hormonal sex reversal and intraline crosses. The clonal nature of these lines was verified by using multilocus DNA fingerprinting and the isozyme locus ADA*. Although these lines might be expected to be monosex in nature (all-female XX or all-male YY depending on the clone), one line did contain both sexes of fish. The presence of males in this gynogenetic clonal line and data from progeny testing of these males suggested that this line was homozygous for an allele or combination of alleles at an autosomal locus or loci which caused female to male sex reversal but with limited penetrance. Outbred clonal lines were also produced by crossing between different inbred clones. J. Exp. Zool. 284:675-685, 1999.