Reproductive Biology of the Commercially Important Portunid Crab, Portunus sanguinolentus (Herbst)

Faculty of Marine Sciences, Centre of Advanced Study in Marine Biology, Annamalai University, Tamil Nadu, India

*Corresponding Author:

Soundarapandian P
Faculty of Marine Sciences
Centre of Advanced Study in Marine Biology
Annamalai University, Parangipettai-608502, Tamil Nadu, India
Tel: 04144-243223
Fax: 04144-243553
E-mail: soundsuma@gmail.com

Received date April 03, 2013; Accepted date May 14, 2013; Published date May 19, 2013

Citation: Soundarapandian P, Varadharajan D, Boopathi A (2013) Reproductive Biology of the Commercially Important Portunid Crab, Portunus sanguinolentus (Herbst). J Marine Sci Res Dev 3:124. doi:10.4172/2155-9910.1000124

Copyright: © 2013 Soundarapandian P, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

The male reproductive system of P. sanguinolentus is bilaterally symmetrical creamy to whitish in colour, composed of a pair of testes, a pair of vas differentia, and a pair of ejaculatory ducts internally, and a pair of pleopods externally as accessory reproductive organs, present on the inner side of the abdominal flab. The vas differentia has been divided into three distinct regions, based on the morphological and functional criteria: Anterior (AVD), Median (MVD) and Posterior (PVD) vas deferens. The gonads of the male measuring below 8.5 cm carapace width (CW) has immature stage, above 10.5 cm CW has mature stage, whereas the CW in between 14.5-10.5 cm was maturing stage. The female reproductive system composed of a pair of ovaries, a pair of seminal receptacles (or) spermatheca, and a pair of oviducts open to the exterior through the female genital opening situated on the left and right sternites of sixth thoracic segment. The ovaries of P. sanguinolentus are categorized into five stages, according to the size, colour and external morphology of the ovaries. They are immature, early maturing, late maturing, ripe and spent. Fifty percent of the female crabs attained sexual maturity when they reached the size of 9.1- 9.5 cm CW. Fifty percent of the male crabs attained sexual maturity when they reached the size of 9.5-10.0 cm CW. However, the smallest berried female attained sexual maturity in the present study was measured at 8.6 cm CW. Based on the change in colour, increase in the size and change in the shape of the berry eggs, three different stages of egg development was observed. Stage-I has pale yellow to deep yellow coloured egg mass was 260.16 ± 0.24 μm. Stage-II has yellow to gray coloured egg mass was 290.2 ± 0.31 μm. Stage-III has deep gray to black coloured egg mass was 340.32 ± 0.34 μm.

Keywords

Fluids; Hormones; Pheromones; Genital system; Three spot crab

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 [1]. The main species supporting the crab fisheries in India are Scylla serrata, S. tranguebarica, Portunus pelagicus, P. sanguinolentus, Charybdis feriata, C. lucifera and C. truncata. 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 [2,3]. The reproductive cycle of crustaceans has been widely studied, mainly of those species that have commercial value or ecological potential [4-6]. Many works have been conducted on various aspects of the reproductive biology of many marine animals [7-9]. Study of gonads, size at sexual maturity and fecundity are important aspects of reproductive biology of crab. This information is often required to manage crab fisheries on sustainable basis. Usually two types of criteria are applied to determine the size at which sexual maturity is attained. One is reproductive criteria or physiological maturity in which developmental stages of male and female gonads and smallest size of berried female is taken as an indication of being sexually mature [10]. Another one criteria is the functional maturity in which the relative growth of chela in males and abdominal width in females, with respect to the body size (Carapace width) is to find out the size at sexual maturity. Size at which male and female brachyuran crabs attain sexual maturity has been worked out by several researchers in portunid crabs; P. sanguinolentus, P. pelagicus, Ovalipes punctatus, O. stephonsoni and Liocarcinus depurator and Scylla species [11-18].

The study of breeding season and fecundity is important to have a full understanding of the population dynamics. Fecundity or reproductive potential can be defined as the number of ova shed during particular spawning season or the number of eggs produced in a single batch of spawning [19,20]. The later one is also known as "batch fecundity". Those who have studied batch fecundity in Portunus species was given by Reeby et al. [21] [22-25]. The recognition of biological data about reproduction is required for judicious management and exploitation of this resource. Hence in the present study, an attempt has been made on the various aspects of reproductive biology of the male and female crabs of P.sanguinolentus, such as morphology of the reproductive tract, gonad development, Gonado Somatic Index (GSI), size at maturity and fecundity.

Materials and Methods

Description of the experimental animal

Systematic position

Phylum: Arthropoda

Order: Decapoda Latreille

Family: Portunidae Rafinesque

Genus: Portunus Weber

Species: P. sanguinolentus Herbst

Nomenclature: Common and vernacular names of P.sanguinolentus in India are given below:

Common name-Three spotted crab (or) Blood spotted crab

Gujarathi-Karachla

Marathi-Khekhada

Kannada-Denji

Malayalam-Kavalan njandu

Tamil-Mukkannu nandu

Telugu-Chukkala peeta

Oriya-Kankda/Cherala petta

Bengali-Lajjaboti kankra

The three spotted swimming crab, P. sanguinolentus, is one of the most common and commercially important crab found along the east cost of India [26,27]. It is commonly known as three-spot swimming crab [28]. In Tamil Nadu, the local fisherman calls as "Mukkannu nandu". This crab got its common name from three prominent red to maroon spots on the posterior part of the carapace. They are widely distributed in the Indo-pacific region from the east coast of South Africa to Hawaician waters [29]. Their size and sex composition varies with depths as the juveniles, and adult males typically inhabit estuaries and inshore waters about 10-30 m deep [30,31]. In contrast, females are abundant in 40-80 m depths [31]. The berried crab mostly burried in the sand. It carries the eggs until complete their development and the larvae hatch as zoea, which drift about in the water current. After hatching, zoea transforms into a megalopa, which acquires benthic habits and grows into juvenile crab.

Distinguishing characters (Plate 1)

Plate 1: Male and female crabs of P. sanguinolentus.

• The carapace is much broader than its length.

• Anterolateral border bears nine spines, of which the posterior most is the longest.

• There is no spine on the posterior border of the arm of the cheliped.

• Behind the chelipeds, the three pairs of legs are normal, and the last pair is oar-like for swimming.

• The anterior pair of abdominal appendages is slender and straight with marginal spines at the tip.

• The colouration of the carapace is characteristically in a dark gray ground colouration, the posterior half of the carapace has three large reddish round spots, of which one is median and two laterals, each spot encircled by a whitish ring.

Distribution: Geographical distribution of P. sanguinolentus ranges from Indo–Pacific, Southern Africa, Red sea, Persian Gulf, India, Pakistan, China Sea, Philippines, Japan, Australia and Tahiti.

Fishery information: Caught all along the Indian Coasts. Common size is 10-12 cm in commercial catches; growing to a maximum size of 15 cm across the carapace.

Areas of abundance/landings: Along the coasts of Tamil Nadu (Chennai), Andhra Pradesh (Kakinada), Kerala and Karnataka.

Peak season: March–June and October to December. Caught in trawl, shore-seine and crab traps.

The crabs for the present study was collected from Parangipattai landing centre (Lat.11°29' N; Long.79°46' E) and brought to the laboratory by using plastic container (Plate 2). The crabs were segregated as male and females. They were weighed individually and the size of the carapace width was measured. Sexes were determined by examining the abdominal morphology

Plate 2: Different size crabs of P. sanguinolentus.

The pleopods and gonopores were analyzed to find out the mating and extrusion of eggs. Presence of the eggs or egg remnants or their absence on pleopods, colour of the egg mass was also noted. The crabs were dissected to study the morphology of the reproductive tract and stages of maturation, size, weight, colour of the gonads and Gonadosomatic Index (GSI). The dissected gonads were measured to the nearest 0.001 g by using the electronic balance, and subsequently, gonadosomatic index was calculated by the following formula.

Recently spawned females with bright yellow or orange coloured eggs were selected for egg counting (Fecundity). To estimate the fecundity, pleopods bearing eggs were removed carefully and the weight of the whole egg mass (berry) was taken to the nearest 0.01 g, then four subsamples of berried eggs (0.1 g) were cut from different locations of the egg mass. Number of eggs in each four sub samples was counted with the help of counting tray under stereomicroscope. Average no of eggs present in the samples was then calculated. In order to find out the total weight of the egg mass, the eggs were removed from the pleopods, and weight of the pleopods was taken. This was subtracted from the weight of the whole egg mass. Fecundity was then calculated by the following formula [23].

N=W×n/w

Where W=total weight of the egg mass only; w=average weight of the four egg samples; n=average number of eggs in the samples; N=total number of eggs (Fecundity).

Results

Morphology of the male reproductive system

The male reproductive system of P. sanguinolentus is bilaterally symmetrical creamy to whitish in colour, composed of a pair of testes, a pair of vas differentia, and a pair of ejaculatory ducts internally, and a pair of pleopods externally as accessory reproductive organs, present on the inner side of the abdominal flab. The testes are flat and highly coiled, roughly in the form of "H" located on the dorsal portion of the hepatopancreas sandwiched between the hepatopancreas and the hypodermis of the carapace, and continuing laterally to the stomach upto vas deferens. Just before the posterior stomach and anterior to the heart, the left and right testis are bridged by a commissure. The testes are connected with the vas deferens through a short small duct called vas efferens. Vas differentia is a pair of elongated and coiled tubules, which extend longitudinally from the posterior testes upto the posterior region of the body. The vas differentia has been divided into three distinct regions, based on the morphological and functional criteria: Anterior (AVD), Median (MVD) and Posterior (PVD) vas deferens. The AVD are white, tightly coiled, and lying on either side of the median line of cephalothorax, posterior to the dorsal part of the stomach. The coils of the AVD increase in size posterio-ventrally and lead into the middle vas deferens, which are milky-white meandering tubules of a higher caliber than both the testes and AVD. The posterior vas deferens are whitish in colour arises from the posterior end of the median vas deferens, which are massive for its proximal part, but gradually narrow before opening to the ejaculatory duct. Each posterior VD is connected with an ejaculatory duct, which is a smooth narrow duct extending between the musculature of the swimming peddles. The ejaculatory duct leads into the slender weak tube like genital papilla (or) penis, which are located at the base of the swimming legs. Each penis passes into the two pairs of abdominal appendages called pleopods (or) gonopods situated in the inner side of the abdominal flab. The first pleopod is made up of two segments, the basal one is broad to the sternal wall and the terminal one is long tube-like and tapering towards the tip, which is actually inserted into the seminal receptacle of the female during copulation. The second pleopod helps in passing the seminal fluids from the penis into the funnel like portion of the first pleopod (Plate 3).

Plate 3: Figure Ia. Disssected male crab with gonad; A-Testis, B-commissure, C-Anterior vasdeferens, D-Heart; b.Male reproductive system; A-Testis, B-Commissure, C-Anterior vasdeferens, D-Median vas deferens, E-Posterior vas deferens, F-Ejaculatory duct.

Developmental stages of male gonads

Immature: The gonads of the immature crabs are small and creamy in colour, on either side of the stomach. Testes and vas differentia are not clearly differentiated. Gonads of males measuring below 85 mm Carapace Width are in immature stage.

Maturing: Testes and vas differentia are well developed and clearly differentiated, and creamy white in colour. Testes are large coiled tube. which spreading laterally and posteriorly to the stomach. Anterior vas differentia has enlarged middle and posterior vas differentia is straight and opaque extending to both the side of the heart.

Mature: Testes showed further enlargement, as vas differentia are coiled and very much swollen occupying full body cavity. The AVD and MVD are enlarged and milky white in colour, PVD enlarged and convoluted, but still opaque. Gonads of males measuring above 105 mm CW are in mature stage.

Gonadosomatic Index (GSI) in male crabs

The Gonadosomatic index of the male and female crabs was studied according to the size and weight of the crab. The GSI of the male crab (0.48) was increased from immature crabs to matured crabs (0.79). The size of the animals was ranging between 8.0-8.5 cm CW to 14.1-14.5 cm CW (Table 1).

Table 1: Mean body weight, Mean gonad weight, Gonadosomatic Index (GSI) of the male crab (Values are Mean ± SD).

Morphology of the female reproductive tract

The female reproductive system composed of a pair of ovaries, a pair of seminal receptacles (or) spermatheca, and a pair of oviducts (open to the exterior through the female genital opening situated on the left and right sternites of sixth thoracic segment). The oviducts pass ventrally from the seminal receptacle. The ovary is surrounded by a fibrous connective tissue, which separates the ovary from the surrounding hemocoel. The ovary is roughly in the form of a 'H' and lies on top of the hepatopancreas, extending on both sides along the anterior margin of the cephalothorax are called anterior horns. The ovaries run in posterior cardial direction to the cardiac stomach and just posterior to the stomach, anterior horns are joined by a commissure. The posterior horns pass posteriodorsoventrally and laterally, and applied dorsally to the seminal receptacles which are sandwitched on either side between the lateral wall of the body cavity and lateral part of the pericardium and the posterior horns extend up to posterior margin occupies all spaces of the body cavity. The posterior horns are equal in size at the posterior end (Plate 4).

Plate 4: Figure IIa: Dissected female crab with ovary, A-Anterior horn, B-Commisssure, C-Heart, D-Posterior horn; b.Dissected ovary, A–Anterior horn, B–Commissure, C-Posterior horn, D–Spermatheca.

Stages of ovarian development: The ovaries of P. sanguinolentus are categorized into five stages according to the size, colour and external morphology of the ovaries. They are immature, early maturing, late maturing, ripe and spent.

Immature: Small, flattened ovaries, white (or) translucent in colour, occupy small areas of the body cavity.

Early maturing: Ovary is larger than previous one, light orange in colour, slightly nodulated, not extending into hepatopancreatic region.

Late matured: Larger ovaries yellowish or orange in colour, nodulated, extending into hepatopancreatic region and occupies almost all the space of the body cavity.

Ripe: Very large ovaries, dark yellow or orange in colour, highly nodulated, hepatopancreas is completely hidden or immersed, ovary fills up all the spaces of the body cavity.

Spent: Small, translucent and greatly reduced ovaries unspawned ova are visible throughout the fibrous connective tissue.

Gonadosomatic Index in females: The GSI in females were increased from1.95 ± 0.37 in immature crabs to ripened crabs 3.97 ± 0.31; however, in spent crab has low value of GSI as similar to immature crabs (Table 2).

Table 2: Mean Body weight, Mean gonad weight, Gonadosomatic index (GSI) of the female crab (Values are Mean ± SD).

Size at first maturity: Fifty percent of the female crabs attained sexual maturity when they reached the size of 9.1-9.5 cm carapace width. Fifty percent of the male crabs attained sexual maturity when they reached the size of 9.5-10.0 cm carapace width. However, the smallest berried female attained sexual maturity in the present study was measured at 8.6 cm carapace width.

Ovigerous females: At the time of spawning, the eggs from the ovary of female crabs were extruded through their gonopores and get attached to the cluster of long and very smooth setae on endopodite of the pleopods. Based on the change in colour, increase in the size and change in the shape of the berry eggs, three different stages of egg development was observed.

• Stage-I

Pale yellow to deep yellow coloured egg mass, no eyespots was visible in the eggs, the mean size of the eggs was 260.16 ± 0.24 µm (Table 3)

Table 3: The colour, shape and size of the berried egg (The values are in Mean ± SE).

• Stage-II

Yellow to gray coloured egg mass, eyespots was observed, mean size of the egg was 290.2 ± 0.31µm (Table 3).

• Stage-III

Deep gray to black coloured egg mass, eyespots and chromatophores were discernible, the mean size of the egg was 340.32 ± 0.34 µm (Table 3).

Fecundity: Seventeen ovigerous females were used for the calculation of fecundity. The fecundity was found to be from 283963 to 967293 eggs, in the animals had the carapace width of 10.6-14.1 cm.

Discussion

The focus of the present day aquaculture was moving towards the development of hatchery technology and crab forming to meet the human protein demand. Berried females are important to start a commercial hatchery, but berried females are not available throughout the year from the wild. So, the production of berried females in a controlled condition is essential. Before that one should know the morphology of the reproductive system and reproductive biology of a particular crab is important.

Morphology of the male reproductive system

The morphology of the male reproductive system of P. sanguinolentus consisting of an "H" shaped structure with a pair of testes, pair of vas deferentia and ejaculatory ducts was similar to the reproductive systems described for other decapod crustaceans in general and Portunid crabs, in particular [32-35]. The descriptions of the testes and commissure of P. sanguinolentus matched the descriptions of P. marmaratus, P. sanguinolentus, C. sapidus, Thenus orentalis, Panulirus laevicauda and Goniopsi cruentata [36-40]. However, did not report the existence of a commissure between the testes of C. opilio and M. branchyodactyla respectively [41,42]. Testes of P. sanguinolentus are tubular organs composed of numerous microscopically visible lobules connected to the semniferous duct; consequently, they have been classified as lobular testes according to the categories (lobular and tubular), and are similar to the previous reports of some other brachyurans [34,40,43,44]. Whereas in few species of Brachyura have tubular testes, such as Menippe mercenaria,Eriocheir sinensis, Chionoecetes opilio, Pachygrapsus crassipes and C. bairdi [45-49]. However, they seem to be distributed along different groups of Brachyura (Majoidea, Grapsoidea and Xanthoidea). Chiba studied that lobular testes are very common in portunid crabs. This is the reasons why some brachyurans have a tubular testicular arrangement, whilst others have a lobular one, is unknown [42,50]. The testes connected to the vas deferens by means of a small duct known as vas deferens has been described in Callinectus sapidus and P. pelagicus [35,43]. Vas deferens (VD) is a pair of elongated and convoluted tubules which extend longitudinally in the posterior region of the body [34,51]. In P. sanguinolentus, the vas deferens was divided into three distinct regions: the anterior, middle and posterior vas deferens as has been reported in other crabs based on their morphological and functional criteria in P. sanguinolentus, C. sapidus, T. orentalis and M. branchydactyla. However, other studies characterized two in G. cruentata, four in S. chacei and D. puligator into as many as eight regions [40,52,53]. Different criteria and different microscopic and macroscopic foci may account for this diversity [40]. The presence of diverticula in the VD of Branchyura has been widely described particularly in spider crabs, which present numerous ramified diverticula in the posterior region of the VD [34,36,37,40,43,53]. Diverticula play an important role in increasing the secretion, absorption and storage of spermatophores and seminal fluids [53,54]. The terminal portion of the reproductive system is the ejaculatory duct, which is a smooth duct extending between the musculature of the swimming pedals, as already described in Brachyura [55].

Developmental stages of male gonads

Very few works have been described for the maturity stages in male crabs. Diesel [56] has described six maturity stages in the males of C. irroratus. Campbell observed five stages of maturation in C. iroratus, based on a modified version of who indicated six stages of gonad development [56]. Krol et al. [57] indicated five stages of maturation in male crab C. amnicola. Haefner [58] reported four different morphometric categories of male gonads in M. branchydactyla. Lawal-Are [59] recognized three stages of maturation based on the testis development in P. pelagicus and P. sanguinolentus. In P. pelagicus, three stages of maturation was reported based on the development of vas deferens by [22].

The morphology of female reproductive system

The female reproductive system of P.sanguinolentus is more or less similar to that of other Portunid crabs. It is closely related with the structure observed by in P. sanguinolentus [34,35]. Almeida and Buckup [32] and Johnson [37] observed similar structure in S. serrata and in C. sapidus. George [35] noticed that the posterior prolongation of the right side ovary is shorter and narrower than the left side in P. sanguinolentus. This condition is also observed in P. sanguinolentus at the present study. Corgo and Freire [60] in Cancer pagurus and Estampador [33] in S. serrata observed that the posterior prolongations of the ovary are connected at the posterior end. In P. sanguinolentus differ from such species by posterior prolongation of the ovaries are permanently separated. In many species of branchyurans, fresh mating female crabs are indicated externally by hardened mass of spermatozoa called sperm plug, together with associated secretions producing from the vulva. Similar observation was made in the present study, as well as the study of Sukumaran and Neelakantan [61]. The mated females inhibit further copulation with other males, by prevent the loss of sperm or keep deletrous materials from entering the female reproductive tract [61,62].

Stages of ovarian development

Stages of ovarian development have been determined based on the morphological and histological analysis of the ovary. In the present study, the morphological analysis of the ovaries of P. sanguinolentus demonstrated that a gradual development of the ovaries confirmed the maturation into five maturation stages. Among different workers who have studied the maturation of ovaries in brachyuran's crabs, there is a little consistency as to the number of maturity stages recognized. Six stages of maturation were recorded by Diesel [56] in rock crab C. irroratus and five stages in Chaceon quinquedens. Hartnoll [63], Parker [64] recorded five maturity stages in P. pelagicus; similarly classified five ovarian developmental stages. Dhas et al. [65] reported four maturity stages, except the spent stage in P. sanguinolentus. In the deep sea golden crab, C. fenneri, the developmental stages were classified into six stages by Sumpton et al. [66]. The microscopical analysis of the ovaries of P. sanguinolentus in the present study demonstrated that a gradual development of the ovaries confirmed the maturation into five maturity stages. The examination of gonad is one of the most accurate techniques, but precise estimates rely on some previous knowledge about specific patterns of growth and reproduction to aid the interpretation of the results, as well as knowledge of shortterm breeding cycle to avoid confusion between spent and immature specimens [67].

Gonadosomatic index

The GSI in females showed clear cyclic pattern, with high values during January-February in P. sanguinolentus and during September and January–February in P. pelagicus [59]. In the present study, the GSI was studied only based on the size and weight of the crab, but not in seasonal wise. The GSI has the great relationship with the size and weight of the crabs.

Size at first maturity

The reproductive capacity of certain crustacean species can be assessed by the study of sexual maturity [68]. The size at onset of sexual maturity in brachyurans can be evaluated considering different criteria, including growth allometry, gonad development stages, presence of spermatic bags or sperm in spermathecas, vestige eggs on the ovigerous areas, or the presence of eggs in the abdomen as was analyzed by several authors [31,69-72]. Sexual maturity in brachyurans has been determined in various ways, based on the analyses of morphological maturity, relative growth criteria and physiological and functional maturity [73]. According to Muino [74] the consecutive changes observed during gonadal development are important because besides enabling and estimate of physiological sexual maturity [74-77]. In brachyuran crabs, chela in males and abdomen in females are considered as secondary sexual characters because of their functions in reproduction [78]. The male crab uses its chela for territorial defense, combat, mating and courtship, as well as in carrying and holding the female during copulation. The abdomen in adult females forms an incubation chamber for the developing eggs, which are attached to the setose pleopods. The increase in relative growth of the male chela and female abdomen at the puberty moult brings these structures to fully functional size at sexual maturity. Hence the relative growth of chela in males and abdomen in females has been used to determine size at which puberty moult occurs or functional maturity attained. Cobo and Fransozo [79] from Cochin, west cost of India, reported that the size of the smallest berried P. sanguinolentus as 8.5 cm CW and the size at maturity range was 8.1-9.6 cm CW. Sumpton et al. [12] who worked out physiological maturity in both male and female P. sanguinolentus from Queensland, Australia, reported that the males and females attain sexual maturity at 8.3 and 7.4 cm CW, respectively. Reeby et al. [13] reported that male P. sanguinolentus attains full sexual maturity (meaning functional as well as physiological) at 8.1-8.5 cm CW from Karwar, west cost of India. They did not work out sexual maturity in P. sanguinolentus.

In south west coast of India, the male and female may undergo a pupertal moult, at a size ranging between 8.0-8.5 cm and 8.0-9.0 cm CW, respectively. Hartnoll [80] reported that male and female attain full maturity at 8.3-8.9 mm CW and 8.1-9.3 mm CW, respectively. In the present study, the smallest berried female attained sexual maturity at 86 mm CW, while the male and female crab attained sexual maturity when those reached the size of 95-100 mm CW and 9.0-9.5 cm CW, respectively. According to the present investigation, it was observed that the functional and physiological maturities occur almost at the same size.

The size at which maturity occurs can vary with latitude or location, and within individuals at any location [59]. Pillai and Nair [81] compared geographic variation in the size of sexually mature females in five species of crabs along the east and west coast of North America. Four of the five species show significant geographic variation in size at onset of maturity. The differences in size at maturity among population of the same species of crab may be attributed to variation in moult increment, and in the number of moults [81]. Environmental factors such as temperature and salinity can also affect size at sexual maturity in crabs. Rhasheed and Mustaquim [82] who investigated the effect of temperature and salinity on size at sexual maturity of female blue crab C. sapidus from nine Texas bay systems, stated that size at maturity can vary along the Texas coast, as temperature and salinity vary from bay to bay. He also mentioned that seasonal and annual variation in temperature and salinity in the bay could also affect size at onset of maturity.

Berried females

Egg bearing females occurs throughout the year, with proportion of females bearing egg masses being peak during three different months August, January and March along Parangipettai coast, whereas November to March in South west coast, whereas December to May and July to August in Calicut coast [83-85]. Peaks of higher breeding intensity may be associated with variation in temperature, salinity, food availability, rainfall and photoperiod [86]. In brachyuran crabs inhabiting tropical waters usually breed throught the year, whereas those found in temperate waters breeds only in certain months [87]. It is generally suggested that near the tropics, reproduction occurs year round because environmental conditions are generally favorable for gonad development [88]. However, both continuous and seasonal reproductive patterns are found in subtropical and tropical regions [89]

Fecundity

Fecundity is defined as the number of eggs produced by an individual female [90]. Fecundity is calculated as the number of eggs carried externally by the female [23]. In general, the fecundity of decapod crustaceans is evaluated as the number of eggs or weight of eggs produced by a female in a single egg batch (Batch fecundity), and is positively correlated with body size (or) weight of females [68]. Fecundity is significantly related to the female crab's carapace width [68]. The larger females have potential to produce more eggs than smaller females [91]. Fecundity is a species specific character, not only regarding the number of eggs extruded in a single batch, but also the frequency of brood production during the life cycle of crustaceans [92].

In general, the fecundity of the similar species was varied between different locations. Ryan [34] reported that the fecundity in P. sanguinolentus was ranged between 961000 eggs to 2250000 eggs. Dhas et al. [65] has reported that feacundity was ranged between 268400 to 668300 eggs from Mangalore. Reeby et al. [21] has been reported that the eggs ranged between 1, 58,608-7,12,526 eggs from Karwar. Kumar et al. [23] reported that the fecundity from Karachi was between 2,25,649 to 5, 24,456 eggs. Kailola et al. [93] have been recorded from Northern Taiwan that the eggs was ranged between 4,10,000 to 24,40,000. In the present study, the fecundity was ranged between 2,83,963 to 9,67,293 eggs.

The fecundity was varied in relation to latitudinal range, habitat structure and food availability [94]. Food availability is the most important factor as feeding factor in paramount for yolk formation [94]. Fecundity determines the reproductive potential of a species and the stock size of its population [95]. Information on fecundity is crucial for the management of crab fisheries [95]. A clear knowledge of the fecundity plays a significant role to evaluate the commercial potentialities of crab stock, and also be used to assess the abundance and reproductive potential of the spawning stock. The discrepancy may be affected by environmental factors, including predation, parasitization and temperature, which may affect the balance between the optimal number and the size of eggs, and also by the loss of eggs during incubation period, and/or during handling as the crabs were obtained from commercial landings [24,96].

The male reproductive system of P. sanguinolentus is bilaterally symmetrical creamy to whitish in colour, composed of a pair of testes, a pair of vas differentia, and a pair of ejaculatory ducts internally, and a pair of pleopods externally as accessory reproductive organs, present on the inner side of the abdominal flab. The vas differentia has been divided into three distinct regions, based on the morphological and functional criteria: Anterior (AVD), Median (MVD) and Posterior (PVD) vas deferens [97,98]. The gonads of the male measuring below 8.5 cm carapace width (CW) has immature stage, above 10.5 cm CW has mature stage, whereas the CW in between 14.5-10.5 cm was maturing stage. The female reproductive system composed of a pair of ovaries, a pair of seminal receptacles (or) spermatheca, and a pair of oviducts open to the exterior through the female genital opening situated on the left and right sternites of sixth thoracic segment. The ovaries of P. sanguinolentus are categorized into five stages, according to the size, colour, and external morphology of the ovaries. They are immature, early maturing, late maturing, ripe and spent.

Fifty percent of the female crabs attained sexual maturity when they reached the size of 9.1-9.5 cm CW. Fifty percent of the male crab's attained sexual maturity when they reached the size of 9.5-10.0 cm CW. However, the smallest berried female attained sexual maturity in the present study was measured at 8.6 cm CW. Based on the change in colour, increase in the size and change in the shape of the berry eggs, three different stages of egg development was observed. Stage-I has pale yellow to deep yellow coloured egg mass, no eyespots was visible in the eggs, the mean size of the eggs was 260.16 ± 0.24 µm. Stage-II has yellow to gray coloured egg mass, eyespots was observed, mean size of the egg was 290.2 ± 0.31µm. Stage-III has deep gray to black coloured egg mass, eyespots and chromatophores were discernible, the mean size of the egg was 340.32 ± 0.34 µm. Seventeen ovigerous females were used for the calculation of fecundity. The fecundity was found to be from 283963 to 967293 eggs in the animal's had the carapace width of 10.6-14.1 cm.

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