Molecular characterization and expression analysis of IL-22 and its two receptors genes in yellow catfish (Pelteobagrus filvidraco) in response to Edwardsiella ictaluri challenge.

Interleukin (IL)-22, as a member of the interleukin (IL)-10 family, is an important mediator between the immune cells and epithelial tissues during infection and inflammation. This study reported the characterization and mRNA expression patterns of Pf_IL-22 gene and its cell surface-associated receptors Pf_IL-22RA1 and soluble Pf_IL-22RA2 genes in yellow catfish (Pelteobagrus filvidraco). The open reading frames (ORFs) of the Pf_IL-22, Pf_IL-22RA1 and Pf_IL-22RA2 genes were 546 bp, 1740 bp and 690 bp in length, encoding 181, 579 and 229 amino acids, respectively. Alignments of the deduced amino acid sequences present that the Pf_IL-22 has a conserved IL-10 family signature motif, and the Pf_IL-22RA1 and Pf_IL-22RA2 have two conserved fibronectin type-III domains. Quantitative real-time PCR (qPCR) analyses showed that the Pf_IL-22 and Pf_IL-22RA1 mRNAs were highly expressed in mucosal tissues such as the fin, gill, intestine, skin mucus and stomach, and were weakly expressed in the kidney, liver and head kidney of adult yellow catfish, indicating that the Pf_IL-22 transcripts may be mainly produced by mucosal immune cells/tissues in healthy yellow catfish. The mRNA expression levels of the Pf_IL-22RA2 gene were high in the muscle and liver, and were relatively low in the spleen and kidney. The mRNA expression levels of the Pf_IL-22 and its two receptor genes were significantly up-regulated in both mucosal tissues (gill, hindgut, and skin mucus) and systemic immune tissues (spleen, head kidney and blood) after Edwardsiella ictaluri challenge. These results indicated that the Pf_IL-22 and its two receptors genes might play an important role in the innate immune defense against bacterial invasion.

Molecular characterization and expression analysis of three TLR genes in yellow catfish (Pelteobagrus fulvidraco): Responses to stimulation of Aeromonas hydrophila and TLR ligands.

Toll-like receptors (TLRs) are one of the most extensively researched pattern recognition receptors (PRRs) and play an important role in the innate immune system. In this study, partial cDNA sequences of the Pf_TLR18 and Pf_TLR19 genes and complete cDNA sequence of the Pf_TLR21 gene were cloned from yellow catfish (Pelteobagrus fulvidraco). The open reading frames (ORFs) of the Pf_TLR18, Pf_TLR19 and Pf_TLR21 genes were 1956 bp, 2262 bp and 2949 bp in length, encoding 651, 753 and 982 amino acids, respectively. The Pf_TLR18 and Pf_TLR19 consist of leucine-rich repeats (LRRs), a transmembrane domain and a Toll/interleukin-I receptor domain, and the Pf_TLR21 only has LRRs and TIR domain. Homologous identity revealed that the Pf_TLR18, Pf_TLR19 and Pf_TLR21 genes have high nucleotide and protein sequence similarity with channel catfish, especially the TIR domains that exhibited the greatest conservation compared to channel catfish. Ontogenetic expression analyses indicated that the mRNA expressions of the Pf_TLR18, Pf_TLR19 and Pf_TLR21 genes could be detected from fertilized eggs to 30 day post-hatching and they exhibited different variation trends after hatching. The three TLR genes were expressed in various tissues, but they were mostly highly expressed in the spleen. The mRNA expression levels of the three genes were up-regulated in the spleen, head kidney, trunk kidney, liver and blood after challenge of killed Aeromonas hydrophila. In addition, the expressions of the three TLR genes were induced to up-regulate in isolated peripheral blood lymphocytes of yellow catfish after stimulation with lipopolysaccharides (LPS), peptidoglycan (PGN) and polyinosinic-polycytidylic acid (Poly I:C). Our findings indicate that the three TLR genes may play a potential role in the host defense against pathogenic microbes. These results will provide valuable information to better understand the function of TLR genes in the innate immune system of yellow catfish.

Changes of ammonia, urea contents and transaminase activity in the body during aerial exposure and ammonia loading in Chinese loach Paramisgurnus dabryanus.

The Paramisgurnus dabryanus was exposed to 30 mmol L-1 NH4Cl solution and air to assessing the change of body ammonia and urea contents and the activities of alanine aminotransferase (ALT) and aspartate transaminase (AST). After 48 h of ammonia exposure, ammonia concentration in the plasma, brain, liver and muscle were 3.3-fold, 5.6-fold, 3.5-fold and 4.2-fold, respectively, those of the control values. Plasma, brain, liver and muscle ammonia concentrations increased to 2.2-fold, 3.3-fold, 2.5-fold and 2.9-fold, respectively, those of control values in response to 48 h of aerial exposure. Within the given treatment (ammonia or aerial exposure), there was no change in plasma, brain and liver urea concentrations between exposure durations. The plasma ALT activity was significantly affected by exposure time during aerial exposure, while the liver ALT activity was not affected by ammonia or aerial exposure. Exposure to NH4Cl or air had no effect on either plasma or liver AST activity. Our results suggested that P. dabryanus could accumulate quite high level of internal ammonia because of the high ammonia tolerance in its cells and tissues, and NH3 volatilization would be a possible ammonia detoxification strategy in P. dabryanus. Urea synthesis was not an effective mechanism to deal with environmental or internal ammonia problem. The significant increase of ALT activity in plasma during aerial exposure, indicating that alanine synthesis through certain amino acid catabolism may be subsistent in P. dabryanus.

Changes in digestive enzyme activities during larval development of Chinese loach Paramisgurnus dabryanus (Dabry de Thiersant, 1872).

The digestive physiology of Chinese loach (Paramisgurnus dabryanus) was studied by assessing the specific and total activities of different pancreatic (trypsin, chymotrypsin, amylase and lipase), gastric (pepsin) and intestinal (alkaline phosphatase and leucine-aminopeptidase) enzymes from hatching to 40 days after hatching (DAH). Larvae were reared at 24.4 ± 0.4 °C and fed with rotifers from mouth opening (4 DAH) to 15 DAH, from 10 to 35 DAH with Cladocera and from 30 to 40 DAH with compound diet. Enzyme activities for trypsin, chymotrypsin, amylase and lipase were detected before the onset of exogenous feeding, indicating that these enzymes were genetically pre-programmed. Most of the pancreatic enzyme specific activities increased until 20 DAH and decreased thereafter. The pepsin activity of Chinese loach was firstly detected at 30 DAH, indicating the appearance of functional gastric gland. Alkaline phosphatase specific activity was detected from hatching onward, showed marked increase and reached the second peak at 20 DAH, while a gradual increase in specific leucine-aminopeptidase activity was observed until the end of the experiment. Accordingly, the larvae of Chinese loach possess a functional digestive system before the onset of exogenous feeding and the digestive capacity gradually increases as development progresses. The abrupt increase in intestinal enzyme activities between 10 and 20 DAH demonstrates onset of juvenile-like digestive mode in Chinese loach larvae. The increase in pepsin activity after 30 DAH indicates the shift from alkaline to acidic digestion in Chinese loach larvae, which may be considered as the onset of weaning.

Out-of-season spawning of largemouth bass in a controllable recirculating system.

Largemouth bass (LMB) production exceeded 0.7 million tons in 2021 and has become one of the most important freshwater aquaculture species in China. The stable and fixed culture cycle led to regular and drastic price fluctuation during the past decade. Strong price fluctuation provides opportunities and challenges for the LMB industry, and out-of-season spawning (OSS) and culture will provide technical support for the opportunities. To induce OSS at a low cost, we established a controllable recirculating system that allows precise thermo-photoperiod manipulation. In the system, four experimental groups were assigned, 18NP (18°C overwintering water temperature, natural photoperiod), 18CP (18°C overwintering water temperature, controlled photoperiod), 16CP (16°C overwintering water temperature, controlled photoperiod), and NTNP (natural water temperature and natural photoperiod), to determine the effects of chilling temperature and photoperiod on spawning performance. OSS was observed in all the experimental groups without significant differences, except NTNP. The manipulated broodstock can re-spawn 3 months later in the next spring in advance. Further analysis of the volume percentage of different stages of oocytes provides a base for excellent regression between the volume percentage of the primary growth stage, cortical alveoli stage, vitellogenesis/maturation stage, and gonadal development/maturation. The results suggest that the volume percentage of oocytes is a better indicator of gonadal development and maturation than the gonadosomatic index. We also found that LMB prefers palm fiber as a spawning nest over gravel. The findings of this work provide important technique guidance for practical OSS of the LMB aquaculture industry and standardization of ovary development and maturation in fish with asynchronous developmental oocytes.

Molecular cloning and expression analysis of interleukin-1ß and interleukin-1 receptor type I genes in yellow catfish (Pelteobagrus fulvidraco): Responses to challenge of Edwardsiella ictaluri.

Interleukin-1ß (IL-1ß) is one of the pivotal early pro-inflammatory cytokines, which play important roles in regulating immune response and inducing a series of inflammatory reactions to infections. Interleukin-1 type I receptor (IL-1RI) is a receptor of the IL-1ß that can mediate IL-1-dependent activation. In this study, partial cDNA sequences of the Pf_IL-1ß and Pf_IL-1RI genes were cloned from yellow catfish (Pelteobagrus fulvidraco). The open reading frames (ORF) of Pf_IL-1ß and Pf_IL-1RI genes encode putative peptides of 280 and 543 amino acids, respectively. The deduced amino acid sequences of these two genes shared highly conserved structures with those from other teleosts. Quantitative real-time PCR results showed that the Pf_IL-1ß mRNA had relatively high expression levels in trunk kidney and blood, and the Pf_IL-1RI mRNA was highly expressed in blood and had relatively high expression level in liver. Ontogenetic expression analyses indicate that the Pf_IL-1ß and Pf_IL-1RI genes may play important roles during the embryonic developmental stages. The mRNA expression levels of Pf_IL-1ß and Pf_IL-1RI genes were up-regulated in the trunk kidney, head kidney, blood, spleen, heart and liver after Edwardsiella ictaluri challenge. Western blot analyses showed that Pf_IL-1ß protein was highly expressed in the spleen and head kidney, but not in the fin of adult individuals. These results suggest that the Pf_IL-1ß and Pf_IL-1RI genes may play significant roles in the immune regulation and defense against E. ictaluri in the yellow catfish.

Effects of 17α-Methyltestosterone and Aromatase Inhibitor Letrozole on Sex Reversal, Gonadal Structure, and Growth in Yellow Catfish Pelteobagrus fulvidraco.

Monosex populations are in demand in many fish species with sexual dimorphism, e.g., better growth performance, higher gonad value, superior ornamental value. From the point of view of research, a monosex population is one of the best materials for investigating sex-determining mechanisms, sex differentiation, and sex-linked markers. Sex reversal of females (phenotypic reversal from XX female to XX male) is the first step in all-female production in species with an XX/XY system for sex determination. In the present study, masculinization of yellow catfish, a species with XX/XY sex determination, was investigated by oral administration of various doses of 17α-methyltestosterone (MT) or an aromatase inhibitor (AI) letrozole (LZ); effects on survival, growth performance, sex ratio, and changes in gonadal structure were evaluated. Three doses (20, 50, and 100 mg kg(-1) diet) of oral MT or LZ were administered to fry from 10 days post-hatching (DPH) to 59 DPH. Oral administration of MT at all doses did not significantly change the ratio of males (45.8%, 33.3%, and 50.0% respectively) compared to the control group (37.5%), while yielding intersex fish at all doses (4.2% to 8.3%). Oral administration of LZ produced a significantly higher proportion of males in all doses (75.5%, 83.3%, and 75.0%, respectively). Additionally, the lowest dose of LZ improved the growth of treated fish compared to the control, and all doses of LZ enhanced spermatogenesis in treated males.

Effects of non-steroidal aromatase inhibitor letrozole on sex inversion and spermatogenesis in yellow catfish Pelteobagrus fulvidraco.

The effects of letrozole (LZ), a potent nonsteroidal aromatase inhibitor (AI), on growth performance, sex inversion, and sex changes were investigated in yellow catfish (Pelteobagrus fulvidraco), which display sexual dimorphic growth. Growth performance was promoted significantly in the low-dose LZ treatment, compared with the control. Four LZ treatments produced dose-dependent male proportions that were significantly higher than that of the control. Histological examination of testes treated by LZ displayed a large amount of spermatozoa and enlarged lobule lumens, indicating that LZ treatments can potentially stimulate spermatogenesis. Changes of sex proportions 45 days after the end of the LZ treatments prove that the female germ cells possess a certain degree of bipotentiality. These results suggest that aromatase activity plays a vital role in sex differentiation, as in other teleosts, with inhibition of aromatase activity by AI bringing about sex inversion.