Principles of Genetics and Breeding

9.1.3.1 Quality evaluation of milt

Quality of the milt changes depending on the pre-monsoon, monsoon and post- monsoon period. The quality of the milt can be evaluated by a series of physical observation on the milt samples.

1. Volume of milt

A healthy Indian major carp on its full gonadal maturity produces 6-10ml milt /kg body mass by hypophysation.

2. Spermatocrit value

This is the unit to express the proportion of total and seminal plasma (volume of sperm : volume of milt) in a sample. The spermatocrit capillaries while filled with milt and centrifuged, at 10000 g for at least 5-10 min, the sediment in the capillary indicate the % packed sperm cells in the milt sample.

3. Sperm cell count

• By using haemocytometer or by spectrophotometry the number of sperm can be counted accurately.
• Spermatozoa concentration in fish range from 2x10⁶ to 5.3x10¹⁰ cells per ml. The optimum spermatozoa population in a milt sample of Indian major carp varied between 2.0x10⁷ and 3.5x10⁷ cells/ml.
• The sperm count become less during early premonsoon and post monsoon (south – west) months.

4. Sperm motility

Motility is the most commonly used parameter to evaluate sperm quality, since sperm must be motile to achieve fertilization. Unlike mammal, teleostean spermatozoa are found immotile in the testis as well as in seminal fluid. Healthy spermatozoa on activation show a vigorous movement. The motility of such activated spermatozoa is evaluated by sixpoint (++++++) scale after adding hundred times of a water to a drop of milt.The motility of sperm can be assessed by following the procedure given below.

1. Place 2 μl of sperm on a clean dry microscopic slide.
2. Add 20 μl of activating solution (for example, deionized water for freshwater species or artificial seawater for marine species)
3. Mix thoroughly and put cover glass.
4. Estimate the percentage of progressively motile sperm using 100X objective in the light microscope.

MOTILITY PERCENTAGE SYMBOL

0-10 +

11-30 ++

31-50 +++

51-70 ++++

71-90 +++++

91-100 ++++++

The carp milt sample which possesses spermatocrit value of seventy, sperm count of 2.0x10⁷ cells and motility symbol of ++++ are considered as quality sample for preservation purpose. The duration of motility of fish spermatozoa ranges from 30 to 300s .