Mitochondrial genome of Onychostoma macrolepis (Osteichthyes: Cyprinidae)

Pathogenicity and inactivated vaccine treatment of Aeromonas veronii JW-4 on crucian carp

Aeromonas veronii is a common bacterium found in a variety of aquatic environments, capable of causing a diverse array of diseases in both aquatic animals and humans. Therefore, evaluating the pathogenicity of A. veronii and implementing measures to control its spread are essential. In this study, a strain JW-4, identified as A. veronii, was isolated from diseased Scaphesthes macrolepis, a grade Ⅱ protected animal in China. To investigate the pathogenicity of the strain, fish were fed with serial levels JW-4 supplemented diet or basal diet (control group 1, CG1) for 28 days (d). Results showed that JW-4 stimulated an immune response, evidenced by an increase in immune-related enzyme activities (GOT and GPT) of serum and liver and an upregulation of genes expression levels (TNF-α and IFN-γ) of liver and spleen, and these effects gradually decreased over time. Histopathological examination revealed that JW-4 could alter the tissue structure of immune organs, such as liver and kidney. These changes were accompanied by vacuolar degeneration, nuclear dissolution, and an increased lymphocyte count. To assess protective effects of a vaccine against this strain, fish were injected with an inactivated vaccine (immunization group, IG) or 0.85% sterile saline (control group 2, CG2) for 28-day observation period, then challenged with JW-4 on the 28th day. The inactivated vaccine enhanced total and specific IgM to A. veronii levels of the fish, resulting in a relative percentage survival of 75% in IG. These findings provide a foundation for identifying pathogenic bacteria and developing more effective prophylactic strategies in aquaculture.

Testicular miRNAs and tsRNAs provide insight into gene regulation during overwintering and reproduction of Onychostoma macrolepis

The late overwintering period and breeding period are two important developmental stages of testis in Onychostoma macrolepis. Small non-coding RNAs (sncRNAs) are well-known regulators of biological processes associated with numerous biological processes. This study aimed to elucidate the roles of four sncRNA classes (microRNAs [miRNAs], Piwi-interacting RNAs [piRNAs], tRNA-derived small RNAs [tsRNAs], and rRNA-derived small RNAs [rsRNAs]) across testes in the late overwintering period (in March) and breeding period (in June) by high-throughput sequencing. The testis of O. macrolepis displayed the highest levels of piRNAs and lowest levels of rsRNAs. Compared with miRNAs and tsRNAs in June, tsRNAs in March had a higher abundance, while miRNAs in March had a much lower abundance. Bioinformatics analysis identified 1,362 and 1,340 differentially expressed miRNAs and tsRNAs, respectively. Further analysis showed that miR-200-1, miR-143-1, tRFi-Lys-CTT-1, and tRFi-Glu-CTC-1 could play critical roles during the overwintering and breeding periods. Our findings provided an unprecedented insight to reveal the epigenetic mechanism underlying the overwintering and reproduction process of male O. macrolepis.

A comprehensive overview of ovarian small non-coding RNAs in the late overwintering and breeding periods of Onychostoma macrolepis

The development of the ovary of Onychostoma macrolepis undergoes distinct annual cyclic changes in which small non-coding RNAs (sncRNAs) could play vital roles. In this study, four sncRNA classes in the ovary, including miRNA, piRNAs, tsRNA, and rsRNAs, were systematically profiled by high-throughput sequencing. In adult ovaries of O. macrolepis, 247 miRNAs and 235 tsRNAs were identified as differentially expressing in the late overwintering period (in March) and breeding period (in June). Some up-regulated sncRNAs in March, such as miR-125-1 and tRFi-Lys-CTT-1, could be involved in inhibiting biomolecule metabolism and enhancing stress tolerance during the overwintering period. Compared with the level expression of sncRNAs in March, some sncRNAs were up-regulated in June, such as miR-146-1 and tRFi-Gly-GCC-1, and could be involved in influencing molecular synthesis and metabolism, enhancing oocyte proliferation and maturation, accelerating ovarian development, and increasing fertilization of oocytes by regulating related target mRNAs. The results suggested that sncRNAs in the ovary of Onychostoma macrolepis not only reflect characteristics of the fish's physiology at different developmental periods, but also directly affect ovarian development and oocyte maturation during the breeding period. In conclusion, these results significantly advance our understanding of the roles of sncRNA during overwintering and reproduction periods, and provide a novel perspective for uncovering characteristics of the special overwintering ecology and reproductive physiology of an atypical cavefish.

Melatonin regulates ATP content and fertilising capacity of Onychostoma macrolepis spermatozoa by inhibiting ROS accumulation during semen storage in vitro

Melatonin (MLT) is an efficient antioxidant that protects spermatozoa against damages caused by oxidative stress. In this study, to maintain good function of Onychostoma macrolepis spermatozoa during semen preservation invitro at 4°C, different concentrations of MLT (0.5, 1 and 2μM) were added to the semen. After storage (0, 24, 48 and 72h), 1μM MLT in semen markedly improved sperm quality, as reflected by better plasma membrane integrity, the relative steady level of reactive oxygen species (ROS) and slower rate of decrease in mitochondrial membrane potential. Activated spermatozoa in semen with 1μM MLT had higher kinematic performance (i.e. percentage of motile and progressive spermatozoa and the beat cross frequency; P<0.05) and longer duration of sperm motility (P<0.05) compared with spermatozoa in semen withother MLT concentrations. Furthermore, 1μM MLT maintained higher ATP concentrations in spermatozoa during semen storage and significantly improved the fertilising capacity of spermatozoa after 72h semen storage compared with the other MLT concentrations. To expand wild resources of O. macrolepis, 1μM MLT can be used as a semen additive to maintain better sperm function and enhance sperm fertilising capacity in artificial insemination (AI).