what are the stages of maturity in fish?...(Maturity Stages of Fishes)

Maturity Stages of Fishes

Introduction

• Maturity Stage: Indicates the ripeness of fish testes and ovaries, determining sexual maturity.

Assessment Methods:

• Macroscopic Analysis: Quick and inexpensive; based on visual inspection of gonads.
• Histological Analysis: Accurate but costly and time-consuming; involves microscopic examination of gonad structures.

Classification of Maturity Stages

• International Council of Exploration of Sea: Suggests seven stages of ovarian maturation.
• Common Research Practices: Often use 5 or 6 stages.

Methodology for Assessment

• Cut open the abdominal cavity to view gonads.
• Estimate gonad volume as a percentage of body cavity (e.g., 15%, 20%).
• Record gonad color.
• Determine sex (male, female, or indeterminate).
• Note gonad texture (e.g., flat, blade-like).
• Repeat for different size groups and categorize based on literature.

Maturity Staging in Indian Major Carps (Labeo rohita)

• Stage I: Resting Phase (Immature) (December-January)

• Characteristics

1. Small, thin, thread-like ovaries

2. Translucent, pale or dirty white color.

3. Occupies a small part of the body cavity.

• Histology: Contains nests of oogonia and immature oocytes.

• Gonadosomatic Index: 1.52 pm 0.15(note:pm=plus or minus)

• Average Oocyte Diameter: 108.43 \pm 7.81 , \mu m

example

• Stage II: Early Maturing Phase (Preparatory) (February-March)

• Characteristics:

1. Ovaries larger, thicker, opaque, light yellowish

2. Occupies about half of the body cavity.

• Histology: Large number of oocytes in stages III and IV.

• Gonadosomatic Index: 1.90 \pm 0.42

• Average Oocyte Diameter: 203.37 \pm 21.92 , \mu m

• Stage III: Advanced Maturing Phase (April)

Characteristics:

1. Increased weight and size; deep yellow color.

2. Occupies two-thirds to three-fourths of the body cavity.

• Histology: Thin ovarian wall, increased vascular supply, fewer immature oocytes.

• Gonadosomatic Index: 8.42 \pm 0.82

• Average Oocyte Diameter: 576.87 \pm 20.97 , \mu m

• Stage IV: Pre-Spawning Phase (Mature) (May-June)

• Characteristics:

1. Enlarged ovaries occupying almost the entire body cavity.

2. Turgid, deep yellow color; visible spherical ova.

• Histology: Large number of ripe eggs.

• Gonadosomatic Index: 13.24 \pm 1.34

• Average Oocyte Diameter: 683.06 \pm 22.28 , \mu m

• Stage V: Spawning Phase (July-August)

• Characteristics:

1. Ovaries very enlarged, turgid, yellow with translucent eggs.

2. Ova extruded with gentle pressure.

• Gonadosomatic Index: 21.44 \pm 1.36

• Average Oocyte Diameter: 785.18 \pm 19.36 , \mu m

• Stage VI: Spent Phase (September-November)

• Characteristics:

1. Flaccid, shrunk, dull-colored ovaries.

2. Reduced vascular supply; some unspawned large ova present.

• Histology: Atretic and discharged follicles, along with stage I and II oocytes.

• Gonadosomatic Index: 4.28 \pm 0.71 

• Average Oocyte Diameter: 378 \pm 18.25 , \mu m

Oocyte Atresia and Post-Ovulatory Follicles

 Atresia: The process where oocytes degenerate and are reabsorbed.

• Notably observed in various stages of ovarian development, especially during the spent phase.

Follicular Atresia and Post-Ovulatory Follicles

Follicular Atresia

• Definition: A degenerative process where oocytes at various developmental stages are lost from the ovary.

• Significance: Major cause of reduced fertility in many species.

Key Features

• Ovarian Follicles: Composed of an oocyte surrounded by theca and granulosa cells.

Process:

• Breakdown of ovarian follicles.

Controlled by hormones, primarily through apoptosis (programmed cell death) of granulosa cells.

Hormonal Regulation:

• Inhibition: Follicle-stimulating hormone (FSH) inhibits atresia and promotes follicle development.

Post-Ovulatory Follicles (POF)

• Definition: Structures formed after ovulation when the follicle tissue collapses around the oocyte.

Characteristics:

1. Remains in the ovary as an evacuated follicle.

2. Serves as indicators of previous spawning activity.

Summary

• Follicular atresia is a natural process that affects fertility by reducing the number of viable oocytes.

• FSH plays a crucial role in preventing this process, allowing for the development of healthy follicles.

• Post-ovulatory follicles provide insight into reproductive history and activity.