Molecular characterization and expression analysis of nine toll like receptor (TLR) genes in Scortum barcoo under Streptococcus agalactiae infection

Toll like receptors (TLRs) are important pattern recognition receptors participating in innate immune system. Up to now, no TLR has been identified in Jade perch (Scortum barcoo). In this study, we successfully identified 9 members of TLRs from the Jade perch. Amino acid sequence alignment analysis showed that the whole sequences of these TLRs were highly conserved among different fish species, especially in LRR, TM and TIR domains. Phylogenetic analysis revealed that each SbTLR was successfully grouped into corresponding gene family of teleosts. Expression analysis showed that most SbTLRs mainly expressed in liver, spleen, muscle and skin, while expressed less in brain and stomach. After Streptococcus agalactiae infection, expression of SbTLR2, SbTLR5S and SbTLR22 were significantly upregulated, while SbTLR3, SbTLR5M, SbTLR9, SbTLR13, and SbTLR14 were significantly downregulated. In all, this research first reported molecular characterization and expression profiles of 9 TLRs in Jade perch. These data will make a contribution for better understanding the antibacterial mechanism of TLRs in teleosts.

De Novo Assembly, Characterization and Comparative Transcriptome Analysis of the Gonads of Jade Perch (Scortum barcoo)

Due to the high meat yield and rich nutritional content, jade perch (Scortum barcoo) has become an important commercial aquaculture species in China. Jade perch has a slow growth rate, taking 3-4 years to reach sexual maturity, and has almost no difference in body size between males and females. However, the study of its gonad development and reproduction regulation is still blank, which limited the yield increase. Herein, the gonad transcriptomes of juvenile males and females of S. barcoo were identified for the first time. A total of 107,060 unigenes were successfully annotated. By comparing male and female gonad transcriptomes, a total of 23,849 differentially expressed genes (DEGs) were identified, of which 9517 were downregulated, and 14,332 were upregulated in the testis. In addition, a large number of DEGs involved in sex differentiation, gonadal development and differentiation and gametogenesis were identified, and the differential expression patterns of some genes were further verified using real-time fluorescence quantitative PCR. The results of this study will provide a valuable resource for further studies on sex determination and gonadal development of S. barcoo.

Transcriptome analysis of the spleen provides insight into the immunoregulation of Scortum barcoo under Streptococcus agalactiae infection

Jade perch (Scortum barcoo) is a freshwater fish with substantial economic value, which has been widely cultivated all over the world. However, with the intensification and expansion of farming, several bacterial and viral diseases have occurred in jade perch. To understand the immune response of jade perch against Streptococcus agalactiae (Group B Streptococcus, GBS), we performed a histopathological examination and transcriptome sequencing of jade perch spleen after artificial bacterial infection. GBS infection can cause structural changes and even necrosis of the jade perch spleen, which may affect the survival of infected individuals. A total of 144,458 unigenes were obtained through de novo assembly of spleen transcriptome. Among them, 1821 unigenes were identified as DEGs, including 1415 up-regulated and 406 down-regulated unigenes in the infection group. Moreover, the analysis of GO and KEGG revealed that many GO terms and pathways were involved in the host immune response, such as Toll-like receptor signaling pathway, Cytokine-cytokine receptor interaction, and TNF signaling pathway. In addition, according to transcriptome data and qRT-PCR analysis, the expression levels of many cytokines that participate in the inflammatory response changed a lot after GBS infection. Overall, this transcriptomic analysis provided valuable information for studying the immune response of jade perch against bacterial infection.

Performance of a recirculating aquaculture system using biofloc biofilters with convertible water-treatment efficiencies

To achieve high water-treatment efficiencies and simplify the setup of recirculating aquaculture systems (RAS), this study examined the use of suspended growth reactors (R1 and R2) based on biofloc technology (BFT) as water-treatment biofilters. Moreover, the conversion of the heterotrophic R1 biofilter to a nitrifying role was investigated. During RAS operation using heterotrophic BFT biofilters, R1 and R2 simultaneously controlled total ammonium nitrogen, nitrite (NO₂^--N), nitrate (NO₃^--N), soluble reactive phosphate (SRP), and alkalinity, with relevant functional microbes including denitrifying bacteria (DNB), phosphorus accumulating organisms (PAOs), denitrifying PAOs (DNPAOs), glycogen accumulating organisms, ammonia oxidizing bacteria, and nitrite oxidizing bacteria. To achieve low concentrations of nitrogen, phosphorus, and save carbon sources, we were able to quickly convert R1 into a nitrifying BFT biofilter by stopping carbohydrate addition. Although there were dominant relative abundances of DNB, PAOs, and DNPAOs in the converted R1, the lack of carbon sources resulted in continuous rise of NO₃^--N in the effluent, stable NO₂^--N removal efficiency, and absence of SRP removal after 40 h. However, R2 retained the previous NO₃^--N and SRP removal efficiencies with carbohydrate addition. This indicated that this novel RAS using BFT biofilters achieved simultaneous nitrogen and phosphate removal, and that the convertible water-treatment efficiencies of BFT biofilters could be controlled by carbohydrate addition. This approach could simplify the RAS setup and meet real-time water quality demands.

The complete mitochondrial genome of jade perch, Scortum barcoo (Perciformes: Terapontidae: Scortum)

This is the first documentation of the complete mitochondrial genome sequence of the jade perch, Scortum barcoo. The 16,843 bp mitogenome containes 37 genes (13 protein-coding genes, 22 transfer RNA genes, and 2 ribosomal RNA genes) and two main non-coding regions (the control region and the origin of the light strand replication) as do other vertebrate mitogenomes. The overall base composition of S. barcoo is 27.39% for A, 24.74% for T, 31.14% for C and 16.73% for G, with a slight A + T bias of 52.13%. All protein-coding genes are initiated with ATG except for COX1, which begin with GTG instead. Meanwhile, the termination codons of 13 protein-coding genes are varied with TAA, TAG, TA, T or AGG. The measure of complete mitogenome sequence of S. barcoo will provide fundamental data for the phylogenetic and biogeographic studies of the Terapontidae.