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Expressed genes and polymorphisms were identified in lines of rohu Labeo rohita selected for resistance or susceptibility to Aeromonas hydrophila, an important bacterial pathogen causing aeromoniasis. All animals were grown in a common environment and RNA from ten individuals from each line pooled for Illumina mRNA-seq. De novo transcriptome assembly produced 137,629 contigs with 40× average coverage.Forty-four percent of the assembled sequences were annotated with gene names and ontology terms. Of these, 3,419 were assigned biological process terms related to "stress response" and 1,939 "immune system". Twenty-six contigs containing 38 single nucleotide polymorphisms (SNPs) were found to map to the Cyprinus carpio mitochondrial genome and over 26,000 putative SNPs and 1,700 microsatellite loci were detected. Seventeen percent of the 100 transcripts with coverage data most indicative of higher-fold expression(>5.6 fold) in the resistant line pool showed homology to major histocompatibility (MH), heat shock proteins (HSP)30, 70 and 90, glycoproteins or serum lectin genes with putative functions affecting immune response. Forty-one percent of these 100 transcripts showed no or low homology to known genes. Of the SNPs identified, 96 showing the highest allele frequency differences between susceptible and resistant line fish included transcripts with homology to MH class I and galactoside-binding soluble lectin, also with putative functions affecting innate and acquired immune response. A comprehensive sequence resource for L. rohita, including annotated microsatellites and SNPs from a mixture of A. hydrophila-susceptible and -resistant individuals, was created for subsequent experiments aiming to identify genes associated with A. hydrophila resistance.

The complement component 9 (C9) plays a significant role in the formation of membrane attack complex (MAC) on the targeted cell surface. The current study is dealt with molecular characterization of C9 gene from rohu, Labeo rohita, an important cultured carp species in India. An open reading frame (ORF) of 1998 bp was amplified by polymerase chain reaction (PCR) that encodes a polypeptide of 666 amino acids having a signal peptide of 19 amino acids and a mature peptide of 647 amino acids. The SMART domain architecture analysis revealed two thrombospondin type‐1 domains (TSP1), a low‐density lipoprotein receptor domain class A (LDLa), a membrane attack complex and perforin (MACPF) domain, and an epidermal growth factor (EGF)‐like domain. Multiple sequence alignment and evolutionary analysis revealed a primitive C9 sequence of rohu with maximum similarity and clustering with common carp, grass carp and zebrafish. C9 was highly expressed in liver and constitutively expressed in wide array of tissues except in eye of rohu juveniles. It was expressed during early developmental days of rohu including in milt. A variable level of up‐regulation in C9 expression was noticed upon poly I:C induction, Aeromonas hydrophila and Argulus siamensis infections in liver, spleen and gill tissues of rohu at different time points. A constitutive expression of C9 in different stages of rohu during the ontogeny and in response to pathogen exposures along with high degree of sequence homology with other fish species proved it as an important primitive immune molecule of the complement system lytic pathway. [ABSTRACT FROM AUTHOR]

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In order to determine the immunomodulatory effect of dietary levamisole in Asian catfish ( Clarias batrachus), fish were fed four different diets for 10 days: a formulated diet as control and the same diet supplemented with 50, 150 or 450 mg levamisole kg−1 feed. The serum bacterial agglutination titre against Aeromonas hydrophila as a measure of specific immunity, serum haemagglutination titre, natural haemolytic complement activity (ACH50), myeloperoxidase and lysozyme activities, total protein level and oxidative radical production by neutrophils as a measure of non-specific immunity as well as disease resistance against A. hydrophila challenge to separate vaccinated and non-vaccinated groups were evaluated at 0, 1, 2 and 3 weeks after last administration of levamisole. Levamisole supplement at the lowest level (50 mg kg−1) significantly enhanced oxidative radical production and serum myeloperoxidase (MPO) content immediately after 10 days of feeding, which reached peak values after 3 and 2 weeks of feeding respectively. Haemolytic complement and haemagglutination titre were significantly enhanced after 3 and 1 weeks respectively. Haemolytic complement activity and MPO activities were significantly raised to 150 mg kg−1 after 3 and 2 weeks, respectively. At the highest level of levamisole feeding (450 mg kg−1) significant decreases in superoxide production and complement activity were measured immediately after levamisole feeding, which returned to the normal level after 1 week post- feeding. Fish were challenged with a virulent strain of A. hydrophila at 0, 1, 2 and 3 weeks after levamisole feeding, and the cumulative per cent survival was recorded over 10 days. Feeding levamisole at 50, 150 or 450 mg kg−1 increased per cent survival in vaccinated fish immediately after levamisole feeding, and survival was significantly higher at 450 mg kg−1. There was no difference in mortality patterns in non-vaccinated fish. The results support the use of levamisole at 50 mg kg−1 feed for 10 days as an immunostimulant in Asian catfish farming. [ABSTRACT FROM AUTHOR]

Selection of fish disease resistance may be performed directly via survival and challenge data or indirectly via the identification of the underlying resistance markers responsible for the differential survival. In a preliminary study, the potential correlation of a variety of specific and nonspecific immune parameters with aeromoniasis resistance was investigated in 13 different fullsib families of rohu (Labeo rohita), one of the important Indian major carp species known to exhibit differential susceptibilities to aeromoniasis in laboratory conditions. The experimental infection of fish through the intraperitoneal route to Aeromonas hydrophila produced mortality ranging from 0 to 100%. The specific immune response as measured through haemagglutination (HA) titre against sheep red blood cells (SRBC) and nonspecific immunity levels (lysozyme activity and natural haemolysin titre) were not found to be significantly different between resistant and susceptible groups. Serum bactericidal activity was found to be higher in groups of rohu resistant to A. hydrophila infection. Nevertheless, significant (P<0.05) positive correlation between serum bactericidal activity and aeromoniasis was observed. Based on the observations, bactericidal activity appears to play a role in resistance against A. hydrophila infection. [Copyright &y& Elsevier]