International Journal of Aquaculture, 2025, Vol.15, No.6, 298-307 http://www.aquapublisher.com/index.php/ija 301 4 Molecular Mechanisms of Gametogenesis and Oocyte Maturation 4.1 Morphological characteristics of follicular development During the breeding process of yellow catfish, the growth of oocytes seems to be a gradual process, but in fact, there is a series of delicate structural changes behind it. Follicular development begins with the active division of granulosa cells, and at the same time, the matrix of cumulus cells gradually forms, which provide necessary support for the growth of oocytes. At the primary stage, the oocyte is surrounded by the granulosa layer and the follicular membrane. The microvilli structure between the cells enables efficient exchange of nutrients and signals back and forth. When the yolk material and organelles continuously accumulate and increase in volume, the germinative vesicles will slowly move to the outside of the oocyte, which often indicates that meiosis is about to resume and ovulation is about to begin. This process consumes a great deal of energy, is highly dependent on ATP generation, and is simultaneously influenced by both intrinsic genetic regulation and external conditions (such as nutrition and hormonal changes) (Martyniuk et al., 2013; Song et al., 2018). If the follicular structure is imbalanced or the coordination between cells is blocked, the probability of generating oocytes with high developmental capacity will significantly decrease. 4.2 Signal transduction pathways in oocyte maturation It is not just a single hormone or gene that controls the maturation of yellow catfish oocytes, but a complete set of interwoven signaling pathway systems. Metabolic status, environmental stimuli, and hormone levels all converge at the molecular level. In the research, leptin was found to be a key "connection point", which can link fatty acid β -oxidation with the process of oocyte maturation. The experimental results show that leptin can up-regulate genes related to β -oxidation such as CPT1, Acsl and ACOX1, and also promote the expression of mature-related genes such as MAPK, Cdc2 and IGF-1R, and activate the JAK-STAT pathway. This signaling system is particularly important for meiosis recovery and germinal vesicle rupture (Song et al., 2018). If β -oxidation is inhibited, the promoting effect of leptin will almost disappear, which shows the core position of metabolic signals in this link. In addition, pathways such as PI3K-AKT and GPCR have also been proven to be involved in regulating follicular development and gametes production (Xiong et al., 2015). The interlaced operation of these signals ultimately affects chromatin remodeling, cytoplasmic reorganization, and whether the oocyte can smoothly enter the fertilization stage. 4.3 Relationship between gamete quality and fertilization rate Whether the yellow catfish can successfully reproduce often does not depend on the quantity but on the "quality" of the oocytes. A high-quality oocyte usually indicates that both the nucleus and cytoplasm are fully mature, with sufficient energy and normal expression of related genes. Studies have found that enhancing fatty acid β -oxidation can significantly increase the maturation rate and diameter of oocytes, and simultaneously activate key genes affecting oocyte ability (Song et al., 2018). Conversely, if metabolism or signal transduction is disrupted, the quality of oocytes will decline, and the fertilization rate and embryo survival rate will also deteriorate accordingly. It is not only the internal metabolism that affects quality, but also the microenvironment around the follicle. The balance of growth factors, antioxidant substances and hormone signals all play a key role (Martyniuk et al., 2013). Therefore, understanding these molecular mechanisms is not only for academic discussion but also can provide practical ideas for aquaculture, such as improving the reproductive efficiency of yellow catfish through nutritional supplementation, hormone regulation or genetic improvement. 5 Artificial Induced Breeding Techniques and Seedling Cultivation 5.1 Hormone-induced and reproduction synchronization techniques Hormone induction is the key technology to achieve synchronous reproduction of yellow catfish. During the breeding season, broodstock with high maturity are selectively induced to undergo labor induction treatment, usually by injecting carp pituitary gland extract or synthetic gonadotropin analogs (such as LRH-A, etc.). By scientifically controlling the injection dose and timing, female fish can be induced to ovulate and male fish can ejaculate, allowing multiple broodstock to spawn and be fertilized at the same time, achieving synchronized reproduction (Kim et al., 2024). Generally, female fish are injected with an appropriate amount of hormones
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