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Sea Ranching of Laboratory Produced Seeds of Blue Swimmer Crab,<em> Portunus pelagicus</em> (Linnaeus) from South East Coast of India | OMICS International
ISSN: 2157-7617
Journal of Earth Science & Climatic Change

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Sea Ranching of Laboratory Produced Seeds of Blue Swimmer Crab, Portunus pelagicus (Linnaeus) from South East Coast of India

P. Soundarapandian1*, D. Varadharajan and T. Anand2
1,2Faculty of Marine Sciences, Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai, 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
E-mail: [email protected]
Received April 10, 2013; Accepted May 14, 2013; Published May 20, 2013
Citation: Soundarapandian P, Varadharajan D, Anand T (2013) Sea Ranching of Laboratory Produced Seeds of Blue Swimmer Crab, Portunus pelagicus (Linnaeus) from South East Coast of India. J Earth Sci Climate Change 4:138. doi:10.4172/2157-7617.1000138
Copyright: © 2013 Soundarapandian P, etal. 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 increased demand for the crabs in different markets and the depletion of resources along the coast has necessitated an urgent need for enhancing crab population. In this juncture, sea ranching is one of the right choice to increase the population. The fecundity rate of P. pelagicus was ranging between 9, 00, 000 to 10, 60,000 eggs in wild collected berried females, whereas 8, 72,000 to 9, 48,000 eggs in laboratory produced berried females. The berried females had similar incubation periods (6-7 days) for both the experimental setups. The hatching success of freshly hatched I zoea was 70% for laboratory produced berried females; however 71% for the wild collected berried females. The larval duration was 26.21 days for wild collected berried females and 26.50 days for laboratory produced berried females. The larval duration did not show significant difference between wild collected and laboratory produced brooders. In both experiments, survival rate was higher in I zoeal stages. The survival rate was decreased regularly when the development proceeds. The survival rate was very low when the V zoea metamorphosed into megalopa. The survival rate did not show significant difference between wild collected and laboratory produced brooders. The laboratory reared crab seeds were released successfully in Pudhupettai one of the coastal village in Parangipettai coast.

Keywords
Berried; Eggs; Survival; Sea ranching; Megalopa; Adult; Wild population
Introduction
India is one of the major contributors of marine crustaceans in the world market [1]. The crab fishery in India is fast developing and there is a vast scope for the crab meat both national and international markets [2-4]. The crab species are not only consumed locally but also exported extensively to the US and European markets as pasteurized crabmeat products [5,6]. Most of the edible crabs caught from marine brackish water environments belonging to the family Portunidae. In seas around India, five genera of Portunid crabs have been reported (Scylla, Portunus, Charybdis, Lupocyclus and Thalamita). In recent times the blue swimming crabs (P. pelagicus and P. sanguinolentus) are fished in large quantities from all the seas in India and finally sold as a processed food [4]. John Samuel [7] has recorded the total annual crab landing were 79,445.6kg in Parangipettai coast, but the recent survey shows that the exploitation of crab sources rapidly increasing as double. The increased demand for the crabs in different markets and the depletion of resources along the coast has necessitated an urgent need for enhancing crab population. In this juncture, sea ranching is one of the right choice to increase the population. In recent years, stock enhancement and sea ranching have been recognized for their potential of increasing and sustaining coastal fisheries [8-11]. Hence in the present study an attempt has been made to release the laboratory reared crab seeds to Pudhupettai coastal areas to restore the decreased population. This will enhance the incomes of fishing villages as well as to supply the seafood so as to meet the market demand in environment friendly way.
Materials and Methods
In Ist experiment the healthy live similar sized crabs of both matured males and females of P. pelagicus were collected from the Parangipettai (Lat. 11°29'N and Long. 79°46'E) landing centre and brought to the laboratory. In the laboratory they were immediately immersed in a prophylactic dip of 200 ppm formalin for 30 min [12]. They were acclimatized with laboratory conditions. After acclimatization the males and females were allowed to mate. After mating the fertilized eggs are extruded through the gonophores present in the sternites of the sixth thoracic segments of third pair of legs and these eggs become attached to the smooth setae present in the endopodites of the four pair of pleopods in the abdominal flab. The egg mass segregated and carried on the abdominal flab is called as berry or sponge. The females carrying eggs is also called as berried crabs. The berried females were stocked in separate tanks for hatching. In experimental setup–II, naturally collected berried female with yellow colour eggs were maintained in separate tank for hatching. The physico-chemical parameters maintained during the experimental period are given in Table 1. During incubation period, the brooders were fed with oyster meat (Crassostrea madrasensis). At every morning left over feed and feacal matter from the tank were removed and half of water was replaced with fresh sea water. Larvae hatched during the early hour of the day. The methodology for the larval rearing was followed by [13]. The developmental stages of the larvae were observed under binocular microscope and classified according to [14]. Fecundity was calculated by weighing the female directly after extrusion and once again after eggs was hatched. From that the total egg mass was calculated as well as fecundity. The Hatching success is the total number of healthy larvae produced. This was calculated by the number of larvae per milliliter of water in a known volume of water.
Statistical analysis
To know the statistical significance between the survival rate and larval duration of wild collected and laboratory produced seeds by using the SPSS/pc+ package16th version.
Live feed culture
Chlorella marina: The inoculum of C. marina was inoculated into the seawater enriched with ammonium sulphate, super phosphate and urea in a ratio of 10:1:1. The green colour developed within 3 to 4 days was the indication of C. marina development.
Rotifer (Brachionus plicatilis): After inoculating the rotifer (30 individuals/ml) was introduced in to the chlorella tank, the yeast was added daily as supplementary feed to the rotifers. After the microscopical observation on 3rd or 4th day rotifer were harvested and to the tank an equal amount of Chlorella with the medium was added for further culture of rotifer. Continuous vigorous aeration was given and the temperature was maintained as 30 ± 2.0°C throughout the culture period.
Artemia nauplii: The Artemia nauplii were harvested from the Artemia hatching tank and placed in a plastic tub with required quantity of water. The enrichment solution (Culture Selco–INVE, Belgium) was added at a concentration of 0.1%. The nauplii were enriched for 12 hours and after washing in seawater the nauplii were fed to the crab larvae.
Larval rearing
Stocking: The newly hatched healthy zoeae were stocked at a density of 50 zoea L-1 in a 100 L plastic tuff (2feet height and 3 feet diameter). During the experimental period, the salinity of the water was 33-35 ppt, temperature 28-31°C, pH 7.5-8.0 and dissolved oxygen close to saturation (5-6 mg L-1).
Feeding: All the 5 zoeal and megalopa stages were fed with rotifers (B. plicatilis) and Artemia nauplii. The I zoea were fed three hours after stocking. The larvae were fed with B. plicatilis at the rate of 5-10 per ml (Zoeae I & II). The III and IV zoea were fed with rotifers at the rate of 10-15 per ml. In addition to rotifers, Artemia nauplii also provided from III zoea onwards. The addition of rotifers was stopped once the zoea reached V stage. The megalopa was provided with Artemia nauplii and bivalve meat. The amount of feed not consumed was carefully noted every morning and the amount of feed was adjusted accordingly. Aeration was given throughout the experiment (Table 2).
Results
Fecundity
The fecundity rate of P. pelagicus was ranging between 9, 00,000 to 10, 60,000 eggs in wild collected berried females, whereas 8, 72,000 to 9, 48,000 eggs in laboratory produced berried females.
Incubation period
The berried females had similar incubation periods (6-7 days) for both the experimental setups.
Hatching success
The hatching success of freshly hatched I zoea was 70% for laboratory produced berried females; however 71% for the wild collected berried females.
Larval duration
The larval duration was 26.21 days for wild collected berried females and 26.50 days for laboratory produced berried females. The larval duration did not show significant difference between wild collected and laboratory produced brooders (Tables 3 and 4).
Survival rate
In both experiments, survival rate was higher in I zoeal stages. The survival rate was decreased regularly when the development proceeds. The survival rate was very low when the V zoea metamorphosed into megalopa. The survival rate did not show significant difference between wild collected and laboratory produced brooders (Tables 3 and 4).
Sea ranching
The laboratory reared crab seeds were released successfully in Pudhupettai one of the coastal village of Parangipettai.
Discussion
Marine fisheries have played a pivotal role in ensuring food and nutritional security of the growing population, employment generation, enhanced income and foreign exchange earnings. The crustaceans have a special place in the Fisheries sector which occupies a unique status in the national economy and provide employment opportunities and food and nutritional security to the growing population in the country. Crustacean fishery is fast developing in India and this fishery earns 60% of the foreign exchange with regard to seafood trade. The lucrative prospect of exporting crustaceans has led to unscrupulous extraction of ovigerous (egg-bearing female) forms. This has had considerable impact on fresh recruitment to existing stocks and a reduction in stock size in the wild. Various species of economically valuable crustaceans are fished along the entire coast of Tamil Nadu. Exploitation of crustacean resources along the Tamil Nadu coast are crabs, lobsters, shrimps whereas crabs and lobsters are caught using traditional gears. Currently lobster resources are over-exploited and the state government has imposed a ban on fishing of lobsters weighing less than 250 gm. However, the fishermen do not abide by this rule in all fishing villages because a 150 gm live lobster fetches them Rs/- 200 to 300. Due to the reduction of lobster resources, the seafood industry has turned its focus to the exploitation of blue crabs.
In the crab fisheries, majority was contributed by the members of the family Portunidae in the Indian waters [15-18]. The marine crab fishery in India is mainly supported by P. pelagicus and P. sanguinolentus, and these two species are together contributing upto 90% of the crab landings in the country [19]. Blue crabs are extensively fished in large quantities in mostly all the seas of India, Bangladesh, Southeast Asian countries and Arab countries [7]. Due to the high demand in local market, the species is exploited heavily from estuaries, inshore waters as well as offshore waters [20]. In India the best potentials of crab resources are seen in the coasts of Tamil Nadu, Kerala and Karnataka and to certain extend in Maharashtra and Gujarat. Tamil Nadu tops the list in crab landing all over India and the coastal belt from Tuticorin to Mallipattinam has been proven as the strongest potential of edible sea crabs [21]. Along the Tamil Nadu coast, two species of blue crabs are found, namely P.pelagicus and P.sanguinolentus. P.pelagicus is found along the entire coast, whereas P.sanguinoletus has a restricted distribution. P. pelaguicus fetches a higher price (Rs/-75–100 per kg) when compared to P.sanguinolentus (Rs/-30–40 per kg). The reason behind this, according to the seafood industry, is that the percentage meat content in P. pelagicus is higher than in P. sanguinolentus. P. pelagicus is found both in rocky and muddy regions in shallow waters [22], whereas P. sanguinolentus prefers muddy substratum and deeper waters. This might be due to the migration of ovigerous female to deeper waters [23].
At present, crab fishing is a major source of income for the artisanal sectors, especially in the Gulf of Mannar and Palk Bay regions, even though it is hampered by money lenders to whom some part of the money (10 %) goes from the daily catch. With increasing blue crab extraction, privately owned boiling units for crabs in major crab landing sites have been set up that advance money to fishermen to exploit more resources from the wild. Mostly, two species of blue crabs P. pelagicus and P. sanguinolentus are targeted by this industry for the extraction of meat. Apart from this a nation-based company is exporting nearly 500 kgs of P. pelagicus and P. sanguinolentus daily. In this the large sized crabs (>100 g) were boiled and transported to Tuticorin, from there the processed frozen meat is being exported. The demand has been increasing for live and whole cooked crabs in different Asian and continental markets which has resulted in indiscriminate fishing activity and hence most of the wild resources are under heavy exploitation now [24]. Though crab fishery is driven by stakeholders, the current focus is on income generated and not on sustainable harvest. If the current rate of exploitation continues, the crab fishery will face the same fate as that of the lobster fishery. Even the state government has not formulated any management plan to stop the decline of blue crab populations, or conserve or increase their stock in the wild. These crabs are mainly found in sea-grasses, coral reefs and rocky regions.
The contribution of crabs to all India marine fish catch was low in the early sixties amounting to 4,000 tones it increased steadily to 25,000 tons by the nineties due to expansion of trawl fisheries [19]. The average annual crab landings during 1975-1981 from the Indian coast are 21,310 tones, forming 10.4% of the total crustacean landings [25]. Rao et al. [26] have estimated the total crab resources of the Indian seas are 43,000 tones and nearly half of the estimated resources are at present being exploited. Out of 8 species of edible crabs listed by Rao et al. [26] S. serrata, P. pelagicus, P. sanguinolentus have been the principle species in the exploited fishery along the coasts of the country. Crab landings along the Parangipettai coast was reported by John Samuel et al. and Radhakrishnan [7,27]. John Samuel et al. [7] recorded 12 commercially important crabs, viz., S. serrata, S. tranquebarica, P. pelagicus, P. sanguinolentus, P. gladiator, P. vigil, C. feriata, C. natator, C. lucifera, C. variegata, C. granulata and C. truncata. The total annual crab landings of the Parangipettai coast were 79,445.6 kg. But in recent survey the total annual crab landings were rapidly increasing as double to the above mentioned. The differences in the crab landings in the past two decades are due to many reasons, including development of improved fishing craft and gear, importance of crab meat in the national and international markets and changes in the environmental parameters etc. Using of mechanized boats with more efficient gears as purse-seine and trawlers contributed much to the increase in fish landings. Therefore these resources are heavily fished without any thinking regarding the sustainability of these resources. Among this total landing the P. pelagicus and P. sanguinolentus constituted around 71% of the total landing forming a major crab fishery along the Parangipettai coast. Moreover nearly 20% of crabs from this landing were brooded females. Among the female crabs caught in bottom set gill nets, ovigerous crabs of P. pelagicus (29.7-35%) and P. sanguinolentus (20.3-45.8%) were found to be dominant in the catch during the post-monsoon period and also considerable numbers of ovigerous crabs were caught during the other seasons along the entire coast [28]. This fishery has been practiced since 1950s and its stock size reduced after 2001 mainly because of juvenile and ovigerous female harvest [29]. The collection of brooders from the sea are a matter of concern. This problem has to be addressed urgently.
There is no viable hatchery technology for crabs and lobsters; the only way of protecting the resources is by management. The increased demand for crabs in different markets and the depletion of resources along the coast has necessitated an urgent need for promoting conservation and management. Conservation and management of commercially important crustacean species like blue swimming crab is a biggest challenge. The promotion of sea ranching is one of the effective method for the conservation and management of overexploited species. Sea ranching is the possible conservative measure to avoid the depletion of sources, restock the overexploited species, increasing the crab landings and to make it available throughout the year. Muthiga [30] recommended the release of juveniles, ovigerous females and recently moulted crabs as a way of preventing overfishing and bringing about sustainable harvesting. The large scale destruction of young crabs would obviously have adverse effect on the crab resources, so the size at maturity for these crabs should be studied and awareness programmes should stress the collection of mature adults, therefore a specific size for harvest is to be fixed. The conservation measures for catching young, undersized and berried crabs should be done by educating the fisherman through audiovisual aids. Awareness should be created among fisher folk to conserve the non-target species. If alive, they can be returned to the water, since most of the crabs can tolerate exposure to atmospheric air and they have the capability of regenerating lost swimming or chelate legs. Segregation of resources should be done in the crafts where they anchor so that they can release non-target species immediately. The fishing areas should be closed or the fishing effort should be minimized for certain period of time or seasonal banning of the shipment of crabs should be done. Certain regulatory measures like, regulation of mesh size, regulation of fishing areas, ban of the destructive gears, promotion of artificial reefs effecting code of conduct for responsible fishing have to be implemented and enforcement of laws like fishing legal minimum size (across the broadest part of carapace) and protection of ovigerous crabs to ensure sustainable growth in this sector. The law breakers should be fined or punished.
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