The complete mitochondrial genome (mitogenome) of the Inimicus japonicus was analyzed by next-generation sequencing in this study. The mitogenome is 16,978 base pairs (bp) long and codes for 22 transfer RNA (tRNA) genes, 13 protein-coding genes (PCGs), 2 ribosomal RNA genes (rRNA), and 1 non-coding control region. The overall nucleotide composition of the mitogenome is: 29.61% for A, 29.16% for T, 25.26% for C, and 15.97% for G. Twenty-two tRNAs range from 67 to 74 bp in length, and 2 rRNA (12S and 16S) were 953 and 1,687 bp long, respectively. Phylogenetic analysis by neighbor-joining (NJ) method indicated that I. japonicus showed considerable genetic similarity (82%), and had a closer relationship in the phylogenetic tree to Synanceia verrucosa.

This study analyzed the complete mitochondrial genome of the short barbeled grunter Hapalogenys nigripinnis (Accession number: MT374064). The complete mitogenome was 16,476 bp long and included 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and a control region. Nucleotide composition of the genome was A: 28.70%, T:27.46%, G: 15.73%, and C: 28.11%. All genes were encoded on the H-strand, except for the NADH dehydrogenase subunit (ND6) and 8 tRNA genes. When compared this sequence with the mitogenome of Chinese black grunt, Korean short barbeled grunter showed difference of 64 bp of nucleotide sequence in 20 genes. Phylogenetic tree was constructed using the neighbor-joining (NJ) method and showed the phylogenetic position of the short barbeled grunter in Korea.

The sexual maturation of the male eel can be induced by injection with human chorionic gonadotropin (hCG). However, sexual maturation via hCG injection results in the irregular production of low quality sperm. Low quality sperm have issues with low fertilization and development rates, even when fertilizing good quality eggs. For the stable production of fertilized eel eggs, the development of an effective technology for the induction of sexual maturation in male eels is needed. The current study used varying hCG concentrations (1 IU/g body weight (BW) or 5 IU/g BW), and injection intervals (once a week or twice a week) for the artificial induction of sexual maturation, in order to observe the treatment effects on the quantity and quality of male eel sperm. In addition, the milt from eels obtained after induction of sexual maturation was collected to compare and analyze the production periods, production volumes, motility, and velocity of the sperm. There was no significant difference in sperm motility or velocity with varying hCG concentrations or injection intervals. However, the treatment group with once weekly injections of 1 IU/g BW hCG began sperm production at 7 weeks, while the treatment group with once weekly injections of 5 IU/g BW hCG began sperm production at 6 weeks. The treatment groups that were injected twice per week with either 1 IU/g BW or 5 IU/g BW hCG began sperm production earlier than the other groups, at 5 weeks. The treatment group with weekly injections of 5 IU/g BW hCG had a sperm production volume of 55.3 ml, higher than those of other treatment groups.

Aquaculture of the commercialized eel, Anguilla japonica, relies heavily on wild-caught glass eel. To assess the potential of producing eel larvae artificially, we observed the flotation, fertilization, hatching, and survival rates of artificially fertilized eggs and hatched larvae from wild female and feminized eels. Body shape changes were observed along with the morphological examination of larvae from 30 days after hatching (dah) to approximately 260 dah. The flotation rates were 97.7% and 92.6%, fertilization rates were 68.7% and 67.6%, and hatching rates were 42.3% and 45.5% in eggs from the wild female and feminized eels, respectively, and the survival rates of hatched larvae at 8 dah were 20% and 22%. Eel larvae from the wild female and feminized eels exhibited similar growth rates and change of body shape until metamorphosis. After 120 dah, the growth rates were better in the eel larvae from the feminized eel than in those from the wild female eel. These results indicate that feminized eels are advantageous for the production of eel larvae and might be practical to be used in the artificial production of eel larvae to facilitate and regularize commercial eel harvesting.

This study aimed to develop a glycoengineered recombinant eel follicle-stimulating hormone (rec-eel FSH) with modified O-linked glycosylation and to establish a stable mammalian cell-based production platform using Chinese hamster ovary DG44 (CHO DG44) cells. To introduce additional sites potentially accessible to O-linked glycosylation, the carboxyl-terminal peptide (CTP) region of the human chorionic gonadotropin (hCG) β-subunit (amino acids 115–145) was inserted between the β- and α-subunits of wild-type single-chain eel FSH (FSH-wt). In addition, a flexible 15-amino-acid linker, [(GGSA)₃GGG], was incorporated between the FSH β-subunit and the hCG β-subunit CTP region to improve the structural accessibility of the CTP sequence, generating the FSH-GGSA-hM-Strep construct. FSH-GGSA-hM-Strep was stably expressed in CHO DG44 cells and purified using Strep-Tactin XT affinity chromatography. Western blotting and silver staining revealed a heterogeneous broad band corresponding to an apparent molecular mass of approximately 54–57 kDa, consistent with extensive post-translational modification. Enzymatic deglycosylation with PNGase F, O-glycosidase, and neuraminidase markedly reduced the apparent molecular mass, indicating that N-linked and O-linked glycans and terminal sialic acid residues contribute substantially to the increased molecular mass and molecular heterogeneity of the recombinant hormone. Functional characterization confirmed that FSH-GGSA-hM-Strep exhibited biological activity and elicited a dose-dependent response through the eel FSH receptor. Receptor stimulation induced rapid, transient ERK1/2 phosphorylation, peaking at 5 min, whereas PKA inhibition with H89 markedly attenuated this early response, supporting the involvement of cAMP/PKA-dependent signaling in ERK1/2 activation. In addition, β-arrestin 1 disruption altered the temporal pattern of ERK1/2 activation, with PKA inhibition abolishing the early response and revealing delayed ERK1/2 phosphorylation, suggesting temporally distinct PKA-dependent and β-arrestin-associated signaling mechanisms. These findings demonstrate that incorporation of the flexible [(GGSA)₃GGG] linker together with the hCG β-subunit CTP sequence represents an effective strategy for generating a structurally modified recombinant eel FSH with engineered glycosylation-associated molecular heterogeneity. The establishment of stable CHO DG44 producer cells provides a potential platform for the scalable production of biologically active glycoengineered eel FSH.

This study aimed to increase the survival rate of yellowtail kingfish (Seriola lalandi) larvae. We investigated, from hatching to the breeding period, the growth and survival rate of larvae as well as the the survival rate upon starvation, yolk resorption, mouth opening time, and change in mouth size. The survival activity index (SAI) of larvae at water temperatures between 20 and 28℃ ranged from 9.2 to 0.9, increasing with low temperatures (p＜0.05). Furthermore, the yolk and oil globule resorption time reduced with elevated temperatures. Thus, the time taken to resorb 95% of the yolk was 72 and 84 hours after hatching at water temperatures of 24℃ and 20 to 22℃, respectively. The time of onset of larval mouth opening (y) showed a linear relationship with water temperature (x) that may be represented as: Y = -12.5X + 82 (r² = 0.959). The correlation between the total length (x) and upper jaw length (y) of the larvae also exhibited a linear relationship, from the onset of mouth opening behavior until 96 hours after and at a water temperature of 22℃, expressed as the equation: y = 0.069x (r² = 0.778). In addition, 72 hours after hatching, the upper jaw length was 0.259 ± 0.039 ㎜; rotifer feed was found in the intestinal tract of larvae from this time point on. Moreover, the total length and survival rate (both 60 days after hatching [DAH]), the annual growth rate (AGR), and specific growth rate (SGR) were 113.79 ±14.74 ㎜, 9.1%, 18.53 ㎜ per day, and 5.48% per day, respectively. Little growth was observed from hatching to 20 DAH; however, the growth rate gradually increased from 20 DAH, until the larvae rapidly grew post 30 DAH.