Transport Stress Induces Skin Innate Immunity Response in Hybrid Yellow Catfish (Tachysurus fulvidraco♀ × P. vachellii♂) Through TLR/NLR Signaling Pathways and Regulation of Mucus Secretion

The transport of live fish is a necessary step for commercial production. The skin of teleost fish is the first non-specific immune barrier against exogenous stimuli, and it plays an important protective role under transport stress. Thus, the aim of this study was to explore the skin responses to transport stress in hybrid yellow catfish (Tachysurus fulvidraco♀ × Pseudobagrus vachellii♂) through transcriptome and biochemical analyses. Water samples were collected during a simulated transport treatment. Biochemical indexes and/or gene expression in blood, skin, and mucus in fish in control groups and transport-stress groups (0 h, 2 h, 4 h, 8 h, 16 h) were assayed. The levels of total ammonia–nitrogen and nitrite–nitrogen in the water increased with increasing transport time. Comparison of skin transcriptomes between the control group and the group subjected to 16 h of transport revealed 1547 differentially expressed genes (868 up-regulated and 679 down-regulated). The results of the transcriptome analysis were validated by analyses of the expression levels of selected genes by qRT-PCR. The results indicated that the toll-like receptors and nod-like receptors signaling pathways mediate the skin’s immune response to transport stress: tlr9, mfn2, and ikbke were significantly up-regulated and nfkbia and map3k7cl were significantly down-regulated under transport stress. With increasing transport time, lysozyme activity and the immunoglobulin M content in skin mucus first increased and then decreased. The number of mucous cells peaked at 8 h of transport stress, and then decreased. The mucus cells changed from types II and IV to types I, II, III, and IV. The amounts of red and white blood cells and the levels of hemoglobin and hematocrit first increased and then decreased during 16 h of transport stress. Together, the results showed that the skin responds to transport stress by activating the immune signaling pathway and regulating mucus secretion. These findings have important biological significance for selecting strains that tolerate transport, as well as economic significance for optimizing the transport conditions for scaleless fish.

Morphological redescription and molecular characterization of Trichodina matsu Basson & Van As, 1994 (Ciliophora, Mobilida, Trichodinidae) infecting Tachysurus fulvidraco (Richardson, 1846) from Chongqing, China

During a survey of parasitic ciliates in Chongqing, China, Trichodina matsu Basson & Van As, 1994 was isolated from gills of Tachysurus fulvidraco. Furthermore, the 18S rRNA gene and ITS-5.8S rRNA region of T. matsu were sequenced for the first time and applied for the species identification and comparison with similar species in the present study. Based on the morphological and molecular comparisons, the results indicate that T. matsu is an ectoparasite specific for the Siluriformes catfish. Based on the analyses of genetic distance, multiple sequence alignments, and phylogenetic analyses, no obvious differentiation within populations of T. matsu was found. In addition, the ‘Trichodina hyperparasitis’ (KX904933) in GenBank is a misidentification and appears to be conspecific with T. matsu according to the comparison of morphological and molecular data.

Development a Set of 46 SNP Markers for the Yellow Catfish (Tachysurus Fulvidraco)

The whole genome resequencing was used to develop single nucleotide polymorphisms (SNP) markers for the yellow catfish (Tachysurus fulvidraco). A total of 46 SNP markers were selected from 5550676 genotyping markers which distributed on 26 chromosomes. Of the 46 SNPs analyzed, 35 SNPs conformed to Hardy-Weinberg equilibrium. The observed and expected heterozygosity of these markers ranged from 0.2519 to 0.771 and from 0.265 to 0.5018, respectively. This set of markers will be of great useful for population genetics of the yellow catfish.

The composition of fish species shows little seasonal variation in eDNA based survey at urban streams

Biodiversity in the city is becoming important as cities are expanded. Thus, the cost-efficient and accurate methodology for the investigation of biota has been consistently demanded. Environmental DNA (eDNA) is one of the emerging tools to supplement traditional survey methods and improve the efficiency of the survey. Summer (from July to August) is the monsoon period in South Korea, so it is excluded from the survey period because of the unstable aquatic environment, the safety of investigators, and accessibility to study sites. On the other hand, spring and autumn (from March to October), excluding the flooding season, are considered suitable times for the survey. This study compared fish composition and distribution by season in summer and autumn using eDNA to identify the change of fish composition and determine the suitability of the eDNA survey for seasonal fish investigation at urban streams. The number of eDNA reads, fish composition, and their community structures was changed according to the season. The total eDNA read was 2.3 times more in October (1,419,062) than in July (3,202,626). In addition, compared to the summer when 13 families and 33 species were detected, 13 families and 35 species were detected in fall. A total of 13 families and 32 species were detected in common. Three species (Acheilognathus rhombeus, Tachysurus fulvidraco, Pungtungia herzi) more were identified, and one (Hemiculter leucisculus) was not detected in October. The result described that the distribution rate of fish species has changed in the study area. Especially, the appearance of invasive species increased from 14 to 20 sites and the habitat range of invasive species was extended in October than July. However, there was no significant difference in richness and diversity except for abundance among fish community structures. This result revealed that eDNA survey methods can identify changes in the composition and distribution of fish by season. Furthermore, based on the little fluctuation in the species appearing according to the season, the study suggested that eDNA can be used to complement traditional survey methods by conducting fish surveys regardless of the survey period.

Growth performance, physiological parameters, and transcript levels of lipid metabolism-related genes in hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂) fed diets containing Siberian ginseng

In high-density aquaculture, fish health can suffer because of excessive feeding, which causes fatty liver disease. Siberian ginseng (Acanthopanax senticosus) has been used as a feed additive to promote animal growth, immunity, and lipid metabolism. In this study, we explored the effects of A. senticosus on the physiology of hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂). A control group and five groups fed diets containing A. senticosus (0.5, 1, 2, 4, and 8 g A. senticosus/kg feed) were established and maintained for 8 weeks. Dietary supplementation with A. senticosus at 4 g/kg promoted growth of the hybrid yellow catfish. Serum total cholesterol (TC) and triacylglycerol (TG) levels at 2 g/kg A. senticosus (TC: 1.31 mmol/L; TG: 1.08 mmol/L) were significantly lower than in the control group (TC: 1.51 mmol/L; TG: 1.41 mmol/L), and 4 g/kg A. senticosus (17.20 μmol/g tissue) reduced the liver TG level compared with the control group (21.36 μmol/g tissue) (P <0.05). Comparative transcriptomic analysis of liver tissue between the control group and the group showing optimum growth (4 g/kg A. senticosus) revealed 820 differentially expressed genes and 44 significantly enriched pathways, especially lipid metabolism pathways such as unsaturated fatty acid and fatty acid metabolism. The transcript levels of five lipid metabolism-related genes were determined by quantitative real-time PCR. The results showed that 2–4 g/kg A. senticosus supplementation reduced the FADS2, ELOVL2, CYP24a, and PLPP3 transcript levels and 4 g/kg A. senticosus increased the DIO2 transcript level (P <0.05), leading to altered synthesis of TG and thyroxine and reduced fat deposition in the liver. Our results show that dietary A. senticosus affects the regulation of fat metabolism and promotes the growth of hybrid yellow catfish. A. senticosus is a healthy feed additive, and the appropriate dietary supplementation rate is 2–4 g/kg.