Blood cell characterization and transcriptome analysis reveal distinct immune response and host resistance of different ploidy cyprinid fish following Aeromonas hydrophila infection.

Aeromonas hydrophila can pose a great threat to survival of freshwater fish. In this study, A. hydrophila infection could decrease blood cell numbers, promote blood cell damage as well as alter the levels of alkaline phosphatase (ALP), lysozyme (LZM), aspartate aminotransferase (AST), total antioxidant capacity (T-AOC), total superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) in immune-related tissues of red crucian carp (RCC, 2 N = 100) and triploid cyprinid fish (3 N fish, 3 N = 150). In addition, the significant alternation of antioxidant status was observed in PBMCs isolated from RCC and 3 N following LPS stimulation. The core differential expression genes (DEGs) involved in apoptosis, immunity, inflammation and cellular signals were co-expressed differentially in RCC and 3 N following A. hydrophila challenge. NOD-like receptor (NLR) signals appeared to play a critical role in A. hydrophila-infected fish. DEGs of NLR signals in RCCah vs RCCctl were enriched in caspase-1-dependent Interleukin-1ß (IL-1ß) secretion, interferon (IFN) signals as well as cytokine activation, while DEGs of NLR signals in 3Nah vs 3Nctl were enriched in caspase-1-dependent IL-1ß secretion and antibacterial autophagy. These results highlighted the differential signal regulation of different ploidy cyprinid fish to cope with bacterial infection.

Effects of dietary Gelsemium elegans alkaloids on intestinal morphology, antioxidant status, immune responses and microbiota of Megalobrama amblycephala.

Numerous plant extracts used as feed additives in aquaculture have been shown to stimulate appetite, promote growth and enhance immunostimulatory and disease resistance in cultured fish. However, there are few studies on the famous Chinese herbal medicine Gelsemium elegans, which attracts our attention. In this study, we used the Megalobrama amblycephala to investigate the effects of G. elegans alkaloids on fish intestinal health after diet supplementation with 0, 5, 10, 20 and 40 mg/kg G. elegans alkaloids for 12 weeks. We found that dietary G. elegans alkaloids at 40 mg/kg improved intestinal morphology by increasing villus length, muscle thickness and villus number in the foregut and midgut and muscle thickness in the hindgut (P < 0.05). These alkaloids also significantly improved intestinal antioxidant capabilities by increasing superoxide dismutase, catalase, total antioxidant capacity and malondialdehyde levels and up-regulated intestinal Cu/Zn-SOD and Mn-SOD (P < 0.05) at 20 and 40 mg/kg. Dietary G. elegans alkaloids improved intestinal immunity via up-regulating the pro-inflammatory cytokines IL-1ß, IL-8, TNF-α and IFN-α and down-regulating expression of the anti-inflammatory cytokines IL-10 and TGF-ß (P < 0.05) at 20 and 40 mg/kg. The expression of Toll-like receptors TRL1, 3, 4 and 7 were also up-regulated in intestine of M. amblycephala (P < 0.05). In intestinal microbiota, the abundance of Proteobacteria was increased while the Firmicutes abundance was decreased at phylum level after feeding the alkaloids (P < 0.05). The alkaloids also increased the abundance of the probiotic Rhodobacter and decreased the abundance of the pathogenic Staphylococcus at genus level (P < 0.05). In conclusion, dietary G. elegans alkaloid supplementation promoted intestine health by improving intestine morphology, immunity, antioxidant abilities and intestinal microbiota in M. amblycephala.

Effects of fasting and re-feeding on mstn and mstnb genes expressions in Cranoglanis bouderius.

The myostatin (mstn) and myostatinb (mstnb) gene of Cranoglanis bouderius were cloned and sequenced and their expressions under nutritional restriction were characterized. The full cDNA sequences of mstn and mstnb were 1878 bp and 1928 bp, containing an open reading frame of 1170 bp and 1119 bp, which encoded 390 and 373 amino acids, respectively. The deduced mstn and mstnb sequence structures were similar to other members of TGF-ß superfamily, including the TGF beta pro-peptide, TGF beta domain, proteolytic processing site and nine conserved cysteines in the C-terminal. In addition, four mstn gene duplications were found in Cranoglanis bouderius. Sequence alignment and phylogenetic tree analyses indicated that the mstn gene and mstnb gene had a close relationship with Siluriformes fish, and the mstn and mstnb genes were roughly classified into two groups. RT-PCR analysis revealed that the mstn and mstnb were expressed in a variety of tissues in Cranoglanis bouderius although the mstn was highly expressed in skeletal muscle and the mstnb was mainly expressed in brain. We speculate that the mstn gene but not mstnb is likely to play a key role in managing muscle growth. A fasting-re-feeding experiment was used to evaluate the effects of starvation on mstn and mstnb expressions in juvenile Cranoglanis bouderius for 5 weeks. The result showed that the mstn and mstnb transcript levels varied among tissues. The mRNA expression levels of mstn in muscle, brain and liver gradually decreased during starvation and returned to the normal level after re-feeding. The mstnb mRNA levels in muscle, brain, liver, spleen, intestine and kidney increased during an early fast time but ultimately decreased with prolonged fasting time. The mstnb transcript levels in muscle, brain and liver increased significantly after re-feeding. In summary, the results supported that the mstn and mstnb may not be limited to control of muscle growth in fish but could also be involved in other biological functions.