Ubiquitin C-terminal hydrolases (UCHLs) are a subset of deubiquitinating enzymes, and are involved in numerous physiological processes. However, the role of UCHLs during gonad development has not been studied in crustaceans. In this study, we have first cloned and analyzed expression profiling of Sp-uchl3 and Sp-uchl5 genes from mud crab Scylla paramamosain. The full-length cDNA of Sp-uchl3 is of 1804 bp. Its expression level in the ovary was significantly higher than in other tissues (p < 0.01), and during gonadal development, its expression in both O1 and O5 stages was significantly higher than in the other three stages of ovaries (p < 0.05), while in T3 it was higher than in the former two stages of testes (p < 0.05). Meanwhile, the full-length cDNA of Sp-UCHL5 is 1217 bp. The expression level in the ovary was significantly higher than in other tissues (p < 0.01). Its expression in ovaries was higher than in testes during gonadal development (p < 0.05). The expression level in the O5 stage was the highest, followed by the O3 stage in ovarian development, and with no significant difference in the testis development (p > 0.05). These results provide basic data showing the role of Sp-UCHL3 and Sp-UCHL5 in the gonad development of the crab.

As rate-limiting enzymes of β-oxidation of fatty acids in mitochondria, the carnitine palmitoyltransferase (CPT) played an important role in regulating energy homeostasis of aquatic animals. However, there was very little research on β-oxidation of fatty acids in crustaceans. In the present study, the full-length cDNA sequences of cpt-1a, cpt-1b and cpt-2 were isolated from the hepatopancreas of Scylla paramamosain, and contained 4206, 5303 and 3486 bp respectively. Sequence analysis showed that the CPT-1A, CPT-1B and CPT-2 encoded proteins with 777, 775 and 672 amino acids respectively, and only the CPT-1A possessed a transmembrane region. In addition, both the CPT-1B and CPT-2 contained conservative functional domains like N-terminal domain and acyltransferases choActase 2, while the CPT-1A lacked. The results of phylogenetic tree indicated that the CPT-1A, CPT-1B and CPT-2 of S. paramamosain gathered together with their corresponding orthologues from crustaceans. The tissue distribution exhibited that the cpt-1a was highly expressed in hepatopancreas, followed by muscle, eyestalk and cranial ganglia, and the muscle, eyestalk and heart were main expressed tissues of cpt-1b. Furthermore, the high expression levels of cpt-2 were mainly detected in hepatopancreas, muscle and heart. The transcriptional levels of cpt-1a, cpt-1b and cpt-2 were significantly up-regulated under chronic low salinity stress. Besides, at the acute low salinity stress condition, the expression levels of cpt-1a, cpt-1b and cpt-2 in hepatopancreas were dramatically increased in 14‰ and 4‰ salinity groups at the 6h and 48h, while the transcriptional levels of cpt-1a, cpt-1b and cpt-2 in muscle were signally up-regulated in 14‰ and 4‰ salinity groups at the 12h and 24h, showing an alternate response pattern. Similarly, the present study found that fasting could markedly increase the expression levels of cpt-1a, cpt-1b and cpt-2 in hepatopancreas and muscle, especially cpt-1a in hepatopancreas as well as cpt-1a and cpt-1b in muscle. The results above indicated that the cpt-1a, cpt-1b and cpt-2 played a crucial part in providing energy for coping with fasting and salinity stress. These results would contribute to enhancing the knowledge of cpt phylogenetic evolution and their roles in energy metabolism of crustaceans.

The importance of a gene’s impact on traits is well appreciated. Gene expression will affect the growth, immunity, reproduction and environmental resistance of some fish, and then affect the economic performance of fish-related business. Studying the connection between gene and character can help elucidate the growth of fishes. Thus far, a collected database containing large yellow croaker (Larimichthys crocea) genes does not exist. The gene having to do with the growth efficiency of fish will have a huge impact on research. For example, the protein encoded by the IFIH1 gene is associated with the function of viral infection in the immune system, which affects the survival rate of large yellow croakers. Thus, we collected data through the published literature and combined them with a biological genetic database related to the large yellow croaker. Based on the data, we can predict new gene–trait associations which have not yet been discovered. This work will contribute to research on the growth of large yellow croakers.

The cryopreservation of ovarian tissues from fish has recently been carried out for several endangered and commercially valuable species. However, previous studies in this context have focused on the cryopreservation of immature ovaries—mainly through slow freezing and vitrification—which requires specialized freezing equipment or higher cryoprotectant concentrations to keep cell viability. Therefore, the aim of this study was to explore a convenient, rapid, efficient and less toxic method for the cryopreservation of ovaries at the stage of vitellogenesis from yellow drum (Nibea albiflora), an economically important marine fish. The ovaries at the stage of vitellogenesis were isolated and cut into blocks of approximately 1 cm³, then cryopreserved with 15% propylene glycol (PG), fetal bovine serum (FBS) and 0.2 M trehalose as cryoprotectants. Finally, the samples were treated using three different freezing procedures, including a −80 °C refrigerator, liquid nitrogen, and their combination. After 7 days, the tissues were thawed and digested, and the cell survival rates and gene expression levels were detected using cell viability assay kits and qRT-PCR, respectively. The results of the viability assay showed that the procedure of ovarian tissue storage at −80 °C in a refrigerator for 1 h, followed by transfer to liquid nitrogen, resulted in the highest cell survival rate (>90%). Furthermore, the germ cells at various phases were of normal size; presented a full, smooth surface and regular shape; and did not show any signs of cell rupture, atrophy, depression, granulation or cavitation. Furthermore, the qRT-PCR results revealed that genes related to reproductive development, such as vasa, foxl2, zp3 and gsdf, were all down-regulated under the optimal protocol, while the expression of the nanos2 gene (which is specifically distributed in oogonia) maintained a higher level, similar to that in the control group. This indicated that the viability of germ stem cells (oogonia) was not weakened after freezing and that oogonia could be isolated from the cryopreserved ovaries for germ cell transplantation. The present study successfully establishes an optimal cryopreservation protocol for ovarian tissues from Nibea albiflora, providing reference for the preservation of ovaries at the stage of vitellogenesis from other species.

Gut microbial communities undergo continuous reorganization during fish development, but changes in microbial persistence and ecological niche strategies across post-juvenile growth remain insufficiently understood. Here, we characterized the gut bacterial communities of cultured Larimichthys crocea across three successive body-size classes: EGC (5–8 g), MGC (39–46 g), and LGC (160–162 g). The three stages were successively sampled from the same cultured population maintained in the same culture pond. At each stage, 15 fish were sampled, and intestinal samples from three individuals were pooled to generate one pooled intestinal sample, yielding five pooled samples per stage. Fish received the same feed formulation throughout cultivation, while feeding quantity was adjusted according to growth. Rarefaction analysis indicated adequate sequencing coverage, and ASV-level community structure differed significantly among growth stages (ANOSIM, R = 0.4698, p = 0.001). Pseudomonadota remained the dominant phylum throughout growth, whereas pronounced restructuring emerged at finer taxonomic resolutions. EGC communities showed a comparatively consistent composition dominated by Methylobacterium, while MGC and particularly LGC exhibited substantial redistribution among dominant bacterial lineages. Stage-specific membership also changed with growth: unique genera increased from 36 in EGC to 48 in MGC and 50 in LGC, whereas stage-specific ASVs showed a nonlinear pattern and peaked in MGC (118, 173, and 124 unique ASVs in EGC, MGC, and LGC, respectively); 88 ASVs were shared across all three stages. Persistent taxa remained numerically important, accounting for 36.34%, 31.59%, and 36.95% of detected taxa in EGC, MGC, and LGC, respectively, but their contribution to total community abundance declined from 90.30% to 75.29% and 68.06%. Conversely, intermittent taxa increased in abundance contribution from 6.80% to 14.85% and 29.17%. Niche-breadth analysis further showed that specialists represented 74.38% of classified taxa and generalists 19.26%. Although generalists remained quantitatively dominant, their contribution declined from EGC to LGC, whereas specialist contribution increased. Growth-associated taxa further showed contrasting trajectories, particularly a progressive decline in Methylobacterium and increase in Aquabacterium. Collectively, these findings reveal pronounced ecological reorganization of the gut microbiota across successive size- and age-associated sampling stages of L. crocea. Because body size and age covaried with chronological sampling time in a single culture pond, these patterns should be interpreted as growth-associated temporal restructuring rather than as effects attributable solely to host growth.

External mucosal surfaces form major interfaces between fish and the aquatic environment, yet their microbial succession during host growth remains incompletely resolved. We characterized the gill and skin mucus microbiota of cultured Larimichthys crocea at three successive body-size stages (5–8 g, 39–46 g, and 160–162 g) using 16S rRNA gene amplicon sequencing. At each stage, 15 fish were sampled, and material from three fish was pooled to generate one pooled sample, yielding five pooled samples for each host-associated group. Four samples of truck-delivered seawater supplied by the same provider used throughout cultivation were included as an environmental reference. Rarefaction curves approached saturation, and amplicon sequence variant (ASV)-level community structure differed significantly among the seven groups (ANOSIM, R = 0.7521, p = 0.001). Early-stage gill and skin mucus communities occupied clearly separated regions of ordination space and showed distinct dominant taxa, whereas large-stage gill and skin mucus communities showed reduced separation and greater similarity in dominant taxonomic composition. At the genus level, 2013Ark19i characterized early-stage gills, Vibrio and Photobacterium were prominent in early-stage skin mucus, and Methylobacterium increased markedly in both large-stage mucosal communities. Although 17 phyla, 67 families, and 69 genera were shared across all groups, only 30 ASVs were universally shared, indicating extensive fine-scale turnover. Dataset-wide prevalence classification further showed that persistent ASVs contributed an increasing fraction of community abundance during growth, rising from 21.93% to 75.48% in gills and from 12.77% to 67.61% in skin mucus. Middle-stage skin mucus contained 1387 group-specific ASVs and the highest transient-ASV contribution among host-associated groups, indicating particularly extensive turnover. Overall, external mucosal microbiota exhibited tissue-specific and non-linear growth-associated reorganization, with pronounced intermediate-stage turnover and increasing abundance dominance of persistent ASVs during later growth.