Search

The objective of this study is to investigate a viable and effective method for artificially breeding the mandarin fish (Siniperca chuatsi) in the out-of-breeding season. The mature development of the female mandarin fish's gonad was induced through precise control of water temperature. Measurements were taken during the temperature control period, including body weight, body height, ovulation rate, relative fecundity and gonadosomatic index (GSI). Serum hormone levels were assessed, and histological sections of gonadal tissues were tracked. Subsequently, a series of experiments were conducted to establish the optimal protocol for hormone-induced ovulation and artificial fertilization. The findings revealed that manipulation and elevation of the aquaculture water body temperature could effectively induce gonad development and maturation in mandarin fish. In the high temperature group (HT, water temperature maintained at 25 ± 1 ℃), 81.25 % of the experimental fish reached maturity within 20 days. Subsequent hormone injection resulted in successful ovulation, normal fertilization, and subsequent incubation of viable young fish. Furthermore, the outcomes of the ovulation test using hormones demonstrated that the pairing of luteinizing hormone releasing hormone (LHRH-A2) and domperidone (DOM) proved highly effective in inducing ovulation in mature mandarin fish in the out-of-breeding season. The ideal dosage for a single injection of this combined hormone was determined to be 6 μg LHRH-A2 and 4 mg DOM / kg of body weight. Employing this optimal hormone dosage resulted in a fertilization rate of 83.23 %, a ovulation rate of 100 %, a relative fecundity of 93.40 ± 17.59 103 / kg and a hatching rate of 88.85 %. The anticipated outcome of these studies is to enhance the artificial breeding techniques for mandarin fish in commercial aquaculture, allowing for year-round production of fertilized eggs.

The estrogen-related receptors (ERRs), a group of nuclear receptors, are the first orphan receptor to be identified. In this study, six errs (errα, errβ, errγ, errγA, errγB, errδ) were first cloned from the gonads of mandarin fish (Siniperca chuatsi). Gene cloning results showed the open reading frames (ORF) of both errα, errβ, errγ, errγA, errγB, errδ were 1302 bp, 1434 bp, 1323 bp, 1566 bp and 1308 bp, coding a 432, 476, 439, 520, 434 and 337 amino acid (AA) peptide, respectively. Tissue distribution analysis showed that errα was relatively highly expressed in heart and muscle both in male and female and errγA was highly expressed in brain, stomach and muscle while the errγB was extremely highly expressed in heart and liver both in male and female. The errβ expressed relatively highly in medulla oblongata and gonad of male and female and kidney of male, while errγ expressed relatively highly in stomach of male and female. Gonad expression pattern revealed that errα, errγ, errγA and errγB were all detected from 5 to 180 day after hatching (dah) in both males and females, and errδ began to express after 60 dah. Moreover, errγ, errγA and errγB were highly expressed in 5–10 dah while errα and errδ were mainly expressed in 60–180 dah. Furthermore, luciferase assay showed that errγ could response to estrogen stimulation by modulating estrogen-signaling pathway in mandarin fish.

Mandarin fish (Siniperca chuatsi) is one of the most important commercial fish in aquaculture in the world. As females grow faster than males, the cultivation of all-female mandarin fish has great economic value and commercial prospects. However, little is known about the molecular mechanism of the early gonad development and sex reversal of mandarin fish. In this study, histological methods and transcriptome sequencing techniques were used to study the early gonadal development and gene expression pattern of genetically female (XX) mandarin fish during MT-induced masculinization. The histological results showed that the labile period of sex differentiation of XX mandarin fish was before 36 dpf and MT treatment before this period could induce complete sex reversal. The transcriptome results showed that the expression levels of a few female-related genes were down-regulated by MT during the morphological differentiation stage to cytological differentiation stage of XX gonad, such as cyp19a1a, foxl2, foxl3, hsd17b1, figla, gdf9, bmp15 and β-catenin, suggesting that the changes of these genes may determine the direction of sex differentiation in mandarin fish. In addition, MT also activated the expression of some male-related genes, such as dmrt1, hsd17b3, hsd11b2, cyp11a1, cyp11b, amh, amhr2, sox9 and gsdf. Some of these genes were activated during spermatogenesis stage, suggesting that the up-regulation of these male-related genes may be the result of sex differentiation rather than the cause. The qRT-PCR results of eight randomly selected differentially expressed genes were basically consistent with the transcriptome results, which proved that the transcriptome data were reliable. These results indicated that the expression of genes related to estrogen synthesis in early development stage may play a decisive role in the direction of sex differentiation in mandarin fish.

Dmrt gene family plays a very critical role in sex determination and differentiation in animals. In this study, dmrt1, dmrt2 and dmrt3 were first cloned from the gonads of mandarin fish (Siniperca chuatsi). The complete open reading frame sequences of dmrt1, dmrt2 and dmrt3 were 891, 1581 and 1419 bp, encoding 296, 526 and 473 amino acids. Multiple sequence alignments revealed that dmrt proteins were highly conserved in teleosts, especially in DNA-binding domain. Tissue distribution analysis showed that dmrt1 expressed mainly in testis, dmrt2 expressed in ovary and dmrt3 expressed in heart, muscle and gonad. Gonad expression pattern revealed dmrt1 mainly expressed in testis after 15 day after hatching, while dmrt2 mainly expressed after 60 dah. After 17α-methyltestosterone treatment, expression levels of dmrt1 and dmrt3 increased significantly, while dmrt2 expression was repressed. Furthermore, luciferase assay showed dmrt1 could activate gsdf-promotor and inhibit cyp19a1a-promotor alone in vitro. These results suggest that the dmrt1 play a most important role in testis differentiation/development and dmrt2 is critical in ovary development in mandarin fish.

A well-known fact about mandarin fish (Siniperca chuatsi) is that females grow faster than males. Mandarin fish that have all-female populations have economic advantages, but traditional neo-male fish are difficult to produce. In this study, indirect feeding of 500 mg/kg 17α-methyltestosterone (MT) to XX mandarin fish (60 dpf, days post fertilization) with completely differentiated ovaries induced secondary sex reversal. At 40 days after MT treatment, 14.7% of mandarin fish with complete reversal was produced, which showed for the first time that XX mandarin fishes with differentiated ovaries still have potentially bisexual germ cells and the plasticity of sex reversal. In the MT treatment group, there was no significant difference in survival compared to the control group. The body weight of the MT treatment group was significantly lower than that of the control group 40 days after treatment (dat) (P < 0.05). During MT treatment, serum 11-KT and T concentrations increased and serum E2 concentration decreased in the MT treatment group, but there was no significant difference in hormone levels between the MT treatment group and the control group. A masculinization of mandarin fish was also confirmed by the expression patterns of sex-specific genes sox9, dmrt1, cyp19a1a and foxl2. A significant amount of sox9 and dmrt1 was expressed in the fish gonads of the MT treatment group, whereas cyp19a1a and foxl2 were minimally expressed in the fish gonads. [ABSTRACT FROM AUTHOR]