A comparison of immune responses and disease resistance in clonal lines of Nile tilapia Oreochromis niloticus L.

Abstract

Five clonal lines of Nile tilapia Oreochromis niloticus were produced and propagated. Three second generation clonal lines (clonal lines A, B and C) were produced from females from the respective clonal lines by meiotic gynogenesis followed by sib mating between female and sex reversed neomales from the same clonal line. Clonal lines D and E were first generation clones produced by meiotic gynogenesis from an XX mitotic gynogenetic daughter of an XY neofemale. Survival rate at both pigmentation and yolk sac absorption stages were poor in the meiotic gynogenetics. No males were observed in any of the clonal lines. Microsatellite loci in multiplex reactions were used for parentage analysis of the clonal lines. Analysis of data revealed that clonal individuals from all clonal lines inherited only maternal alleles. The specific immune response were studied in Clonal lines A and B. an outbred clonal line OBC (AXB) and an unrelated control group of Nile tilapia following immunisation with SRBC, DNP-KLH and TNP-LPS. The specific immune response of clonal line A was significantly higher than clonal line B. The OBC (AXB) line had an intermediate response between clonal lines A and B, which was significantly higher than clonal line A and significantly lower than clonal line B. The response of URC was lower than clonal line A but the difference was not statistically significant. The experimental groups of fish had similar patterns of specific immune response after being vaccinated with heat killed Aeromonas hydrophila T4. The experimental challenge with A. hydrophila T4 revealed an inverse relationship between antibody production and susceptibility to disease. Clonal line A had significantly lower mortality than clonal line B. Mortality in OBC (AXB) was significantly higher than clonal line A and significantly lower than clonal line B. Lymphocytes isolated from peripheral blood, spleen and head kidney of the experimental groups of fish were stimulated with T -cell mitogen Con A and B-cell mitogen LPS. No correlation was found between polyclonal activation of lymphocytes of healthy fish and specific immune response or disease resistance in the same clonal line.