What is fecundity?
Fecundity
derived from the word fecund, generally refers to the ability to reproduce. In
biology, fecundity is the potential reproductive capacity of an organisms or
population, measured by the number of gametes (eggs), seed set or sexual
propagates. Fecundity can be defined as the number of ova that are likely to be
laid by a fish during the spawning season. Or, the fecundity is the measurement
of reproductive capacity of female fish.
How can it be estimated? What type of relationship is observed between fecundity, length and weight?
Methods of Estimation:
•
Volumetric Method:
•
Total number of the
ovary is measured
•
Ovaries are cut into
small pieces and random samples are taken from anterior, middle and posterior
part of the ovaries.
•
The number of ova
from each sample is counted along with the volume.
•
The total number of
the ova and total volume of the ovary is then calculated.
•
Gravimetric Method:
•
The formalin
preserved ovaries are used.
•
The weight of the
ovary is measured
•
The ovary is cut into
three samples of 100mg each by assumption from anterior, middle and posterior
part.
•
The number of ova
from each sample is counted along with the weight.
•
Total number of ova
is then calculated by following formula:
F = (S×OW)/100
Where, F = Fecundity
S = Average number of ova obtained from three
samples of 100mg each.
OW = Total weight of the Ovary
•
Quantitative method:
•
By this method the
fecundity is estimated after fertilization only.
•
Fertilization was
performed by mixing the eggs and the sperm adding water and shaking the
petri-dish by hand.
•
Excess sperms are
removed and the fertilized eggs are left for 10 minutes to get water hardened.
•
After being
fertilized the after hardened eggs are photocopied and a piece of thick white
paper was used to cover the petri-dish while eggs after photocopied.
•
White circles were
counted and recorded as viable eggs, and dark dots counted as dead eggs.
•
Scanned Image Method
•
The ovaries are
collected and kept on ice until they could be weighed and gravimetric
subsamples could be dissected.
•
Each sub samples was
then preserved in Gilson’s Fluid (0.015l nitric acid, 0.008l glacial acetic
acid, 0.1l 60% ethyl alcohol, 0.877l distilled water for 1l of fluid) to
promote the breakdown of ovarian tissues.
•
After exposure of
four to six weeks, the eggs are rinsed and dewatered using a 333-am square mesh
screen and low vacuum suction.
•
Eggs are then
dispersed in petri dish and any large clumps are gently separated. We used 100
mm diameter plastic (round) petri-dish, which are tended to produce low optical
aliases when scanned.
•
Concentration of the
eggs alongside of the dish is to be avoided by using melted agarose gel mixed
with 15l of water.
•
After the agarose
hardened, an image of the dish was taken by placing the dish directly on
flatbed scanner. The cover of the petri-dish is painted black which can produce
high resolution images of the eggs on black background.
•
The image was saved
as gray-scale at a pixel resolution of (600×600 dpi).
•
Scans were then
examined using image processing and the eggs are counted.
What is the importance of knowledge about fecundity?
Estimation
of Fecundity is Important in respect of fisheries science due to the following:
- This is important in the field of
population ecology. Fecundity can be increased or decreased in a
population according to the current conditions and certain regulating
factors. For instance, in times of hardship for a population such as a
lack of food, juvenile and eventually adult fecundity has been shown to
decrease.
- The estimation is important to know the relation between the length and weight of the fish. In fish farming, the estimation helps to understand which size group would be economical and profitable for maximum production of new offspring.
0 Comments