IMPORTANCE OF SHELLFISH HATCHERY IN BANGLADESH

INTRODUCTION:Shellfish is a culinary and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environments, some kinds are found only in freshwater. In addition a few species of land crabs are eaten.

WHAT IS SHELLFISH? :

Shellfish, a group of invertebrates and aquatic organism, is covered by chitinous or calcareous exoskeleton.  Shell means an outer covering or layer which is popularly known as “Kholos” in Bengali. Shellfish belongs to two major Phylum Arthropoda and Mollusca. In Bangladesh there are a wide range of shellfishes have been found which comprises different groups such as, Crustaceans (shrimp, prawn, lobster, crayfish, and crab) Molluscs (clam, mussel, oyster and scallop), and others (squid, octopus and snails, sea urchins, etc). Despite the name, shellfish are not a kind of fish, but are simply animals that live in water. Many varieties of shellfish (crustaceans in particular) are actually closely related to insects and arachnids, making up one of the main classes of the phylum Arthropoda. Cephalopods (squid, octopus, cuttlefish) and bivalves (clams, oysters) are molluscs, as are snails and slugs.Familiar marine molluscs enjoyed as a food source by humans include many species of clams, mussels, oysters, winkles, and scallops. Some crustaceans commonly eaten are shrimp, lobster, crayfish, and crabs. Echinoderms are not as frequently harvested for food as molluscs and crustaceans, however sea urchin roe is quite popular in many parts of the world.

Figure: Shellfish

SHELLFISH HATCHERY:

A fish hatchery is a "place for artificial breeding, hatching and rearing through the early life stages of animals, finfish and shellfish in particular". Hatcheries produce larval and juvenile fish (and shellfish and crustaceans) primarily to support the aquaculture industry where they are transferred to on-growing systems i.e. fish farms to reach harvest size. Some species that are commonly raised in hatcheries include Pacific oysters, shrimp, Indian prawns, salmon, tilapia and scallops. The value of global aquaculture production is estimated to be US$98.4 billion in 2008 with China significantly dominating the market, however the value of aquaculture hatchery and nursery production has yet to be estimated. Additional hatchery

production for small-scale domestic uses, which is particularly prevalent in South-East Asia or for conservation programmes, has also yet to be quantified.

Figure: Tanks in a shrimp hatchery

IMPORTANCE OF SHELLFISH HATCHERY IN BANGLADESH:Hatcheries produce larval and juvenile fish and shellfish for transferal to aquaculture facilities where they are ‘on-grown’ to reach harvest size. Hatchery production confers three main benefits to the industry;

1. Out of season production:Consistent supply of fish from aquaculture facilities is an important market requirement. Broodstock conditioning can extend the natural spawning season and thus the supply of juveniles to farms. Supply can be further guaranteed by sourcing from hatcheries in the opposite hemisphere i.e. with opposite seasons.

2. Genetic improvement : Genetic modification is conducted in some hatcheries to improve the quality and yield of farmed species. Artificial fertilization facilitates selective breeding programs which aim to improve production characteristics such as growth rate, disease resistance, survival, color, increased fecundity and/or lower age of maturation. Genetic improvement can be mediated by selective breeding, via hybridization, or other genetic manipulation techniques.

3. Reduce dependence on wild-caught juveniles : In 2008 aquaculture accounted for 46% of total food fish supply, around 115 million tones. Although wild caught juveniles are still utilized in the industry, concerns over sustainability of extracting juveniles, and the variable timing and magnitude of natural spawning events, make hatchery production an attractive alternative to support the growing demands of aquaculture.

4. Sources of broodstock: Prawn hatcheries require an uninterrupted supply of berried females during the season. For the consistent operation of hatcheries broodstock are collected at regular intervals. The principal sources of broodstock to prawn hatcheries are wild and prawn farm. According to the survey, 33% of hatcheries use natural broodstock, 13% use farm-reared broodstock and the remainder (54%) both sources. In those hatcheries using both sources, it is believed that broodstock are commonly being sourced from prawn farms rather than wild.

5. Spawning: Natural spawning can occur in hatcheries during the regular spawning season however where more control over spawning time is required spawning of mature animals can be induced by a

variety of methods. Some of the more common methods are:

a) Manual stripping   : For shellfish, gonads are generally removed and gametes are extracted or washed free. Fish can be manually stripped of eggs and sperm by stroking the anaesthetized fish under the pectoral fins towards the anus causing gametes to freely flow out.

b) Environmental manipulation : Thermal shock, where cool water is alternated with warmer water in flow-through tanks can induce spawning. Alternatively, if environmental cues that stimulate natural spawning are known, these can be mimicked in the tank e.g. changing salinity to simulate migratory behavior.

c) Chemical injection : A number of chemicals can be used to induce spawning with various hormones being the most commonly used.

6. Fertilization:Prior to fertilization, eggs can be gently washed to remove wastes and bacteria that may contaminate cultures. Promoting cross-fertilization between a large number of individuals is necessary to retain genetic diversity in hatchery produced stock. Batches of eggs are kept separate, fertilized with sperm obtained from several males and allowed to stand for an hour or two before samples are analyzed under a microscope to ensure high rates of fertilization and to estimate numbers to be transferred to larval rearing tanks.

7. Larvae:Rearing larvae through the early life stages is conducted in nurseries which are generally closely associated with hatcheries for shellfish culture whilst it is common for shellfish nurseries to exist separately. Nursery culture of larvae to rear juveniles of a size suitable for transferal to on-growing facilities can be performed in a variety of different systems which may be entirely land-based, or larvae may be later transferred to sea-based rearing systems which reduce the need to supply feed. Juvenile survival is dependent on very high quality water conditions. Feeding is an important component of the rearing process. Although many species are able to grow on maternal reserves alone (lecithotrophy), most commercially produced species require feeding to optimise survival, growth, yield and juvenile quality. Nutritional requirements are species specific and also vary with larval stage. Carnivorous fish are commonly fed with live prey; rotifers are usually offered to early larvae due to their small size, progressing to larger Artemia nauplii or zooplankton. The production of live feed on-site or buying-in is one of the biggest costs for hatchery facilities as it is a labour intensive process. The development of artificial feeds is targeted to reduce the costs involved in live feed production and increase the consistency of nutrition, however decreased growth and survival has been found with these alternatives.

8. Settlement of shellfish:The hatchery production of shellfish also involves a crucial settling phase where free-swimming larvae settle out of the water onto a substrate and undergo metamorphosis if suitable conditions are found. Once metamorphosis has taken place the juveniles are generally known as spat, it is this phase which is then transported to on-growing facilities. Settlement behaviour is governed by a range of cues including substrate type, water flow, temperature, and the presence of chemical cues indicating the presence of adults, or a food

source etc. Hatchery facilities therefore need to understand these cues to induce settlement and also be able to substitute artificial substrates to allow for easy handling and transportation with minimal mortality.

PRESENT STATUS OF SHELLFISH IN BANGLADESH:

A list of mussels and snails species found in Bangladesh is given here-(Here, F= Freshwater; B= Brackish water;   M=Marine; CR= Coastal region; E=estuary; ID= Insufficient data)

Mussels:Sl Scientific name English name Habitat Distribution1 Mytilus edulis Blue mussel M Ccoasts of Britain, Morecambe Bay, and

estuaries of southwest England, west Scotland and west Wales.

2 Perna viridis Green mussel CR Intertidal coasts of India3 Perna Indica Brown mussel CR Intertidal coasts of India4 Septifer sp. Box Mussel M Indo-West Pacific.5 Chlanys sp. Box Mussel Indo-West Pacific.

Snails:Sl Scientific name English name Habita

tDistribution

1 Turbo sp. Turban Shell M Indo-West Pacific.2 Neritia sp. Nerite B Indo-West Pacific, Eastern part of the Indian

Ocean and the tropical West Pacific.3 Cerithium sp Cerith E Indo-West Pacific, from the west coast of

India and Srilanka to eastern Malayasia.4 Terebralia sp. Mud Creeper CR Indo-West Pacific, from East Africa to

Melanesia5 Acutangula sp. Turret shell M Found in all seas6 Maculatus sp. Maculated Top M, CR Indo-West Pacific7 Monodonta sp. Top Shell M, CR Indo-West Pacific.8 Arabica (top) Cowry M Indo-west Pacific.9 Fusinus sp. Nicobar Spindle

fusiformM Indo-West Pacific.

10 Fasciolaria sp. Tulip Shell M Caribbean Province & Bay of Bengal11 Latirus sp. Many Angled

SpindleM Indo-West Pacific

12 Thais sp. Rock Shell M Probably widespread in the Indo-west Pacific but frequent confusion with similar Species

13 Indica sp. Turrit Shell M, CR Indo-West Pacific14 Oliva sp. Olive Shell M, CR Tropical west Pacific, Indo- West Pacific.15 Murex sp. Murex Shell CR Indo-West Pacific16 Textile sp. Cone Shell M, CR Indo-West Pacific.17 Mitra sp. Meter Shell CR Central Indo-West Pacific18 Pila globosa Freshwater apple

snailF North-Central India to Bankok

19 Lymnaea stagnalis

Stagnant pond snail F British Isles: Great Britain and Ireland, Canada (Alberta province), Cambodia, Czech Republic – least concern (LC), Germany – distributed in whole, Germany

but in 2 states in red list (Rote Liste BRD), Netherlands, Poland, Russia – Sverdlovsk oblast, Slovakia, Sweden (Skåne), Switzerland, Ukraine

20 Melanoides tuberculata

Live bearer snail F Northern Africa , South Africa and also found in Asia (Bangladesh, China, India (including Andaman Islands), Japan, Laos, Malaysia (Peninsular Malaysia), Nepal, Saudi Arabia, Sri Lanka, Vietnam,Thailand

21 Telescopium telescopium

Telescope shells M Mainly found in Madagascar but somewhat in this subcontinent also

22 Viviparus begalensis

Data are not available

ID -

23 Viviparus variata

Data are not available

ID -

24 Bythinia Stenothyroides

Data are not available

ID Found in India and adjacent countries

25 Mysorella costigera

Data are not available

ID Karnataka (A. Madhyastha pers. obs.) and a few specimens collected in Madras, Tamil Nadu, southern India and Sri Lanka

26 Assiminia brevicula

Salt marsh snail, Red mangrove snail

B Asia; India, Sri Lanka, Philippines, China (including Hong Kong), Taiwan, Malaysia, Indonesia, Myanmar, Singapore, Thailand, Viet Nam, Japan and Thailand.Native in Bangladesh; China; Hong Kong; India (West Bengal); Japan; Malaysia; Myanmar; Philippines; Singapore; Sri Lanka; Taiwan, Province of China; Thailand; Viet Nam

27 Sulcospira variabilis

F Malaysia, China, Thailand, Indonesia, and Vietnam and also in Bay of Bengal

28 Lymnea pinguis No common name recorded

29 Pyla viren - - -30 Anisus

convexiusculus- - -

Oyester:Sl Scientific name English name Habitat Distribution1 Ostrea edulis Native oyster E, CR Norwegian Sea south through the North Sea

down to the Iberian Peninsula and the Atlantic coast of Morocco. Found in the Mediterranean Sea and extends into the Black Sea.

2 Crassostrea belcheri

Edible oyster M

3 Srassostrea cucullata

Edible oyster M Indo-Pacific including the Red Sea, recorded in the Suez Canal

4 Crassostrea madrasensis

Edible oyster CR South-West and South-East coasts of India

5 Pinctada sp. Pearl oyster CR South-East coasts of India

CONCLUSION:

Despite strong demand of broodstock by the hatcheries there is no broodstock bank in Bangladesh. Due to the scarcity of wild broodstock supply to the hatcheries, it is urgently needed to establish a broodstock bank in shellfish farming areas. To meet a part of immediate demand for quality broodstock, both the public and private sector should come forward to establish their own broodstock banks. Hatcheries could be linked to the public and private broodstock bank to ensure the availability of quality broodstock. It would also necessary to encourage private entrepreneurs to start commercially producing good quality broodstock. Rearing broodstock of good quality requires special techniques and fresh spawns from the nature. Improving the quality of broodstock will result in better quality spawns, reduce mortality rate and increase productivity. However, concerns may arise about the sustainability of broodstock banks in terms of technical, biological, environmental and economic aspects. It is therefore necessary to provide institutional and organisational support and government support for sustainable development of broodstock banks. In addition, broodstock rearing techniques to be developed to maintain genetic quality. Moreover, a certification system should be developed and implemented to maintain the quality. Training of broodstock bank operators in areas of stocking, feeding, rearing and harvesting should be provided. It is also necessary to improve handling and transportation practices to reduce the mortality of broodstock.

REFERENCE:1. http://en.wikipedia.org/wiki/Shellfish2. http://en.wikipedia.org/wiki/Fish_hatchery3. http://en.bdfish.org/2012/03/shellfishes-of-bangladesh-mussel-snail-oyster/4. http://mvshellfishgroup.org/shellfish-importance.php5. http://www.enaca.org/modules/news/article.php?storyid=17776. http://www.google.com.bd/url?

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