Characterization of the ceruloplasmin gene and its potential role as an indirect marker for selection to Aeromonas hydrophila resistance in rohu, Labeo rohita.

Ceruloplasmin is an acute phase protein found to be activated by the host immune system during stress conditions. The ceruloplasmin gene has been reported in several teleosts and here we characterize the gene and test its association with resistance to Aeromonas hydrophila in rohu, Labeo rohita. A ceruloplasmin mRNA sequence of 3355 base pairs (bp) was derived (GenBank ID: JX010736). The coding sequence (CDS) comprised of 3276 bp that coded for 1092 amino acids. Alignment results showed the greatest similarity with zebrafish followed by channel catfish sequence, and a phylogenetic tree constructed on the basis of amino acid sequences showed that rohu shares a common clade with these two species. In the ontogeny study, the expression of ceruloplasmin was detected at 9 h post-fertilization onwards, and a strong level of expression was detected at 24 h (38-fold) and 15 days (34-fold) post-fertilization. The ceruloplasmin transcripts were evident in liver, spleen, stomach and heart. Expression was undetectable in gill, brain, eye, skin, muscle, intestine, anterior and posterior kidney tissues. Expression of ceruloplasmin after A. hydrophila infection was up-regulated 6 h post-challenge and was modulated until 15 days post-challenge. The level of ceruloplasmin was also compared in rohu selectively bred for higher growth and disease resistance. The gene showed a 4.58-fold higher level of expression in resistant line over susceptible line rohu selected based on family challenge test survival to A. hydrophila. Serum ceruloplasmin levels in three year classes of rohu selected for higher growth showed a positive correlation (0.49 ± 1.11) with survival against challenge with A. hydrophila. The estimated heritability was also found to be quite high (0.50 ± 0.22) for this parameter. Thus, ceruloplasmin could be one of the useful marker traits for selection against A. hydrophila resistance in fish.