The document summarizes key aspects of the reproductive biology of crabs. It describes how sexes can be identified based on abdominal flap shape. It outlines the male and female reproductive systems, including testicles, ovaries, and seminal receptacles. Size at sexual maturity is detailed for two crab species. Mating, spawning, hatching, fecundity, and seasonal spawning are also summarized.

1. Reproductive biology of crab
Submitted by
Ankita Thakur
B.F.S.C. 2nd year

2. INTRODUCTION
• The crab fishery in India is fast developing, and there is a vast scope for the crab meat, both
national and international markets.
• Crabs rank third next to the shrimps and lobsters for their esteemed seafood delicacy and also the
value of fishery they support.
• The main species supporting the crab fisheries in India are Scylla serrata, S. tranguebarica,
Portunus pelagicus.
• Reproduction is the main mechanism to maintain species proliferation and continuity, and in
brachyuran crabs, is extremely diversified ultimately shaped to maximize egg production and
offspring survivorship.
• The reproductive cycle of crustaceans has been widely studied, mainly of those species that have
commercial value or ecological potential.

3. IDENTIFICATION OF SEXES
• Sexes can be morphologically distinguished based on the shape of the abdominal flap.
• Though the shape of this flap is similar in both immature and mature male , it is different in mature
and immature female.
• In mature female the shape of abdominal flap is half round , while in immature female it is broad
and triangular.
• Study of gonads, size at sexual maturity and fecundity are important aspects of reproductive
biology of crab.

5. REPRODUCTIVE SYSTEM
MALE REPRODUCTIVE SYSTEM
• The male reproductive system is composed of
two testicles, a vas deferens, and ejaculatory
ducts on the inside, and two pleopods and
supplementary reproductive organs on the
outside, located on the inner side of the
abdomen.
• Small genital papilla are formed as the
ejaculatory ducts open. Non-motile sperms and
seminal plasma make up the ejaculate. Sperms
are kept in the vas eferentia and are helped out
of the ejaculatory ducts by pleopods.
FEMALE REPRODUCTIVE SYSTEM
• A pair of ovaries, seminal receptacles, two
oviducts, four pairs of pleopods (externally),
and a few ancillary organs make up the female
reproductive system.
• The majority of the oviduct, which contains the
seminal receptacles, opens to the outside through
the female genital opening at the sixth thoracic
segment.

6. CONTINUE…..
• When the carapace width rises above 90 mm,
both males and females reach sexual maturity.
The three phases of sexual development are I
immaturity (creamy/transparent colour and
lack of noticeable vas deferens), (ii)
maturation (cremy white occupying 1/4 of the
body cavity), and (iii) maturity (milky white
occupying the entire body cavity).
• There are three stages of ovarian development,
including I immature, with a yellowish or
translucent colour and no obvious seminal
receptacle (ii) Mature: Orange red colour with
a conspicuous seminal receptacle occupying
the complete body cavity, and (iii) Mature:
Pink in colour, occupying 1/3 of the body
cavity.

7. SIZE AT MATURITY
The size range at first maturity in males and females of S. tranquebarica and S. serrata is presented in
the Table below
Size range at first maturity in S. tranquebarica and S. serrata Species S.tranquebarica S.serrata.
Species Sex Size range at first maturity
Sylla tranquebarica Male 125-133 mm
Female 129-135 mm
Sylla serrata Male 80-89 mm
Female 85-96 mm

8. MATING
Mating is the fundamental requirement for the natural seed production of mud crabs. The aim of this
study was to develop an induced mating technique of orange mud crab, Scylla olivacea in captivity to
support sustainable mud crab farming through increasing the supply of hatchery-produced mud crab
seeds. Induced mating technique involved the mating of a mature induced soft-shelled female (newly
molted) with a mature intermolt male. The mating pairs were selected randomly.
A mating success of 83.33 ± 5.77% was obtained in captivity using this technique, and can be applied
in future breeding and hybridization trials of mud crabs.

9. SPAWNING
• The female produces ova, which are
then fertilised by sperm kept in the
spematophores.
• The ovigerous setae of the abdominal
appendages are where the fertilised eggs
are attached.
• Females with eggs attached to their
abdomen are known as berried.
• In S. tanquebarica, the number of eggs
per female of body weight may range
from 0.5 to 2.5 million.

10. HATCHING
• The embryos grow throughout the two weeks
when the berried females carry their eggs.
• The eggs' colour transitions from orange to
grey to brown.
• The eggs turn grey-black just before
releasing the larvae.
• The larvae emerge after the incubation
period.
• The newly hatched larvae require food to
grow.

11. FECUNDITY
Pre-spawning fecundity was estimated by counting the
number of ova present in the mature ovary ( Jayamanna
and Jinadasa, 1993 ). Ovaries in stages III and IV were
carefully removed and fixed in Gilson fluid. To calculate
fecundity, the mature ovaries were wiped in a blotting
paper to remove moisture, and then pieces of 0.5 g each
were dissected out from the anterior, middle and posterior
regions of the ovary and each piece into five sub-samples
to an accuracy of 0.01 g using an electronic weighing
balance. Later, each sub-sample was squeezed in 100 ml
distilled water and again sub-samples ( triplicates ) , each
of 1 ml , were taken using a pipette and the number of
ova in each subsample was counted under a binocular
microscope . The obtained values of fecundity ( F ) were
correlated with variables such as CW , BW and OW .

12. SPAWNING SEASON
• It is Seasonal changes in gonado - somatic index ( GSI ) as well as percentage of mature females
were taken into consideration for the prediction of spawning season in S. olivacea at Pichavaram .
Every month , adult crabs were randomly collected based on their dark widened abdominal flap .
For GSI estimation , female gonads were dissected , weighed and calculated using the following
equation :
GSI = Weight of ovary ( g ) /;Weight of the animal ( g ) x 100
Further ,
ovigerous females and spent crabs ( predictable by the swollen spermathecae ) were recorded.