Sea cucumber ; life history

SEA CUCUMBER

Submitted byArya

udayan 2014-01-14

Life Cycle Of

INTRODUCTION

HOLOTHURIANS , Commonly called as sea slugs or Sea cucumbers is a group of economically important Echinoderms.

World wide distribution About 1200 species are

recorded ;; Along indian coast HOLOTHURIA SCABRA ( SAND FISH ) is predominant.

Sea cucumbers consumed either fresh or boiled or prepared as different delicacies.

FAO Statistics indicate a downward trend in world sea cucumber harvest through natural fisheries;hence attempts have been made to promote holothurian fisheries.

REPRODUCTION HOLOTHURIAN SCABRA attains a

length of 400mm & weight of 500g. Lives on Sandy muddy bottom &

sexually mature at 18 months. Size at first maturity is 210mm. Sexes are separate & there is no

distinct sexual dimorphism . It breed twice in an year; 1stspawning

season:march to may & 2nd during October to December Gonadal development is distinguishable

into 5 stages such as immature , resting , growing , mature & post spawning phases .

During immature and resting stage ; ovarian tubules are transparent , short & thin distal end of tubules are club shaped .During growing phase ;tubules are having opaque spherical oocytes of 20 – 120 microns in diameter .

In mature phase ; tubules are swollen containing ripe oocytes of 150-200 In post spawning phase ; some tubules are seen as in mature stage , others are shorter showing atresia , a few ripe oocytes are in the tubules &signs of resorption / atresia are seen.

In males ;During immature & resting phase : testes is hardly distinguishable from ovary .During growing phase testis tubules become more branched & whitish , length & diameter also grow ,spermatids develop inside the tubules .During mature phase tubules grows larger in size,more whitish with swelling & spermatozoa are seen in tubules .During post spawning phase ;tubules appear evacuated with few spermatozoa Ripe testes are milky white whereas

ovaries are translucent .

life history Holothurians usually spawn in late afternoon or evening or during night . During spawning , males release spermatozoa first & then female releases the eggs. Males lift the anterior end and perform swaying movements for sometime after which they start releasing sperm & it continues for 1-2 hours. Ripe females,if present exhibit responsive behavior Anterior region of female gets bulged & eggs are released through gonopore forcefully in a continuous jet.

The mass of eggs so released appear light yellow and mucus like . Fertilization is external ; taking place in water. One adult female releases about 1million eggs . Eggs are spherical , about 180 to 200 µ in size. After fertilization ,first polar body appears after 20-30minutes. First cleavage take place after 15 minutes. In 3 hours the blastula is fully formed . Gastrula is fully formed after 24 hours. The AURICULARIA LARVA hatches out after 48hours. It grows to DOLIOLARIA larva within 10 days . Within 2 to 3 days it develops to PENTACULA stage. They transform into JUVENILES within one month.

life history

Auricular ia larvae It is transparent ,pelagic and measures 560µ. It is slipper shaped & performs locomotion by the movement of flagella of the ectodermal cells that forms ridges or bands. The larva has a digestive tract consisting of mouth , pharynx , stomach & anus. There are 3 coelomic sacs; Hydrocoel & right and left somatocoel . Hydrocoel is connected to hydropore on the dorsal side by means of a tubular canal .

Doliolaria larvae Doliolaria larvae is barrel shaped

measures more than 620 microns in size.

There is partial degeneration of flagellated bands leaving short pieces that joins to form 3 to 5 numbers of flagellated rings.

The hydrocoel encircles the foregut ;develops to 5 lobes which represents the 1

Immediately after ; sixth lobe is developed which is called polian vesicles.

From the water ring , radial water canals are formed.

Pentacula stage Pentacula stage is tubular & it

creeps over the sides and bottom.

It measures 600-700 microns in size.

It has five tentacles at the anterior end & a single tube foot at the posterior end which helps in its locomotion.

They feed on benthic algae and other detritus matter.

They transform into juveniles within one month.

conclusionHolothurians commonly called as

sea slugs or sea cucumbers.H.scabra(sand fish) predominant in

indian coastNo sexual dimorphism & Breeds

twice in an year.Fertilization is external.Gastrula (after 24 hrs ) ,

Auricularia larvae(48 hrs ) , doliolaria larvae( within 10 days) ,pentacula stage etc are the development stages.

References Breeding & seed production of fin

fish & shell fish.[Dr.P.C.Thomas;;Page no : 270]

Hand book of fisheries & aquaculture .[page:590]

Advances in sea cucumber aquaculture & management ,issue 463,FAO [Page no :270-280].

Sea cucumbers [ Jody . S. Rake] [page :57]

Chapter : Hotspot of sea cucumber fisheries in India.

Thank you