Please give me some information about reproductive cyclic change in the ovary of catla catla

The reproductive cycle of the Catla catla, a freshwater fish commonly found in South Asia, is characterized by distinct stages of ovarian development. The cycle involves complex hormonal and physiological changes in the female fish’s ovary, regulated by environmental factors such as temperature, photoperiod, and water quality. Here’s a detailed explanation of the reproductive cyclic changes in the ovary of Catla catla:
1. Stages of Ovarian Development in Catla catla:
The ovarian cycle in Catla catla can be divided into several stages, each with specific morphological and physiological characteristics:
A. Pre-vitellogenic Phase (Resting Stage):

• Duration: This phase occurs during the non-reproductive period, typically after spawning and before the next breeding season.
• Ovary Appearance: The ovary is small, translucent, and not visibly swollen. The oocytes (immature eggs) are in an early developmental stage, called oogonia or primary oocytes.
• Cellular Activity: The primary oocytes undergo mitotic divisions, and the ovary remains relatively inactive in terms of egg maturation.
• Hormonal Activity: Low levels of gonadotropins (hormones that stimulate the gonads) and estrogen are present. The ovary is preparing for the next reproductive cycle.

B. Vitellogenic Phase (Yolk Formation):

• Duration: This is a crucial stage in the ovarian cycle, where oocytes start to grow and accumulate yolk material.
• Ovary Appearance: The ovary becomes larger and more opaque as yolk accumulates in the oocytes. The oocytes transition from primary oocytes to vitellogenic oocytes, which are filled with yolk.
• Cellular Activity: The oocytes grow rapidly in size, and vitellogenesis (yolk formation) begins. The yolk contains proteins, lipids, and other materials necessary for embryo development after fertilization.
• Hormonal Activity: There is an increase in follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which stimulate the ovarian follicles. Estrogen levels also rise, promoting the development of yolk in the oocytes.

C. Maturation Phase (Final Maturation):

• Duration: This phase occurs just before ovulation, leading to the release of eggs.
• Ovary Appearance: The ovaries are large, swollen, and exhibit mature oocytes that are ready for ovulation. These mature oocytes are fully yolked, and the ovary may appear yellowish or orange due to the yolk.
• Cellular Activity: The oocytes undergo the final stages of maturation, including the breakdown of the follicular cells surrounding the oocytes, and the nucleus of the oocyte undergoes meiotic division (reduction division).
• Hormonal Activity: The LH surge triggers ovulation, and there is a peak in prolactin and estrogen secretion, preparing the ovary for egg release. At this point, the oocytes are fully mature and ready to be released into the body cavity for fertilization.

D. Spawning (Ovulation):

• Ovary Appearance: The mature eggs are released from the ovaries into the body cavity and are ready for fertilization by the male sperm.
• Cellular Activity: The mature eggs are released into the oviduct and eventually into the surrounding water for external fertilization.
• Hormonal Activity: The surge in luteinizing hormone (LH) is critical for ovulation. This hormonal surge triggers the rupture of the ovarian follicles, releasing the eggs.

E. Post-Spawning (Regressing Phase):

• Duration: After ovulation, the ovary begins to regress as the remaining yolked oocytes undergo reabsorption or atresia.
• Ovary Appearance: The ovary shrinks in size and appears empty or translucent. If fertilization does not occur, the eggs will disintegrate, and some oocytes will undergo atresia.
• Cellular Activity: Oocytes that did not mature properly are reabsorbed by the body.
• Hormonal Activity: Hormone levels decrease after spawning, and the ovary enters a resting phase in preparation for the next reproductive cycle.

2. Environmental Factors Affecting Reproductive Cycle:
Several factors influence the reproductive cycle of Catla catla, including:

• Temperature: Temperature plays a significant role in the timing of gonadal maturation and spawning. In Catla catla, spawning usually occurs during the warm months, typically during the monsoon season when water temperatures are around 25°C–30°C.
• Photoperiod: The light cycle can influence the timing of gonadal maturation. Longer days in the pre-monsoon period help trigger reproductive readiness in Catla catla.
• Water Quality: Clean, oxygen-rich water is essential for the healthy development of eggs and larvae. Poor water quality can impair the gonadal development of Catla catla and hinder successful spawning.
• Hormonal Regulation: The reproductive cycle is also regulated by external hormones like gonadotropins, and the availability of these hormones in the environment can affect the maturation of the ovaries.

3. Spawning Period of Catla catla:

• Season: The spawning season for Catla catla typically coincides with the monsoon season, which is from June to September in South Asia. This is when environmental conditions such as water temperature, turbidity, and flow are optimal for spawning.
• Spawning Frequency: Catla catla is a seasonal spawner and spawns only once or twice per year, depending on environmental conditions.

Conclusion:
The reproductive cycle of Catla catla involves multiple stages, from the pre-vitellogenic phase through to the post-spawning regression. The key stages are:

1. Pre-vitellogenic: Resting stage with immature oocytes.
2. Vitellogenic: Yolk formation and oocyte growth.
3. Maturation: Final maturation of oocytes.
4. Spawning: Release of mature eggs.
5. Post-spawning: Ovarian regression and reabsorption of unripe oocytes.

Environmental factors such as temperature, photoperiod, and water quality play a critical role in regulating these stages and ensuring successful reproduction in Catla catla.