Indian Journal of Marine Sciences Vol. 31(2), June 2002, pp. 150-152

Short Communication

Intercapsular embryonic development of the big fin squid Sepioteuthis lessoniana (Loliginidae)

V. Deepak Samuel & Jamila Patterson*

Suganthi Devadason Marine Research Institute, 44, Beach Road, Tuticorin – 628 001, Tamil Nadu, India

( E.mail : jamilapat@hotmail.com ) Received 18 June 2001, revised 22 January 2002

The egg masses of big fin squid, Sepioteuthis lessoniana were collected from the wild and their intercapsular embryonic development was studied. The average incubation period of the egg varied between 18-20 days. The cleavage started on the first day and the mantle developed between third and fifth day. The yolk started decreasing eighth day onwards. The tentacles with the sucker primordia on the tip were prominent from tenth day. The yolk totally reduced between thirteenth and seventeenth day and the paralarvae hatched out on eighteenth day.The developmental stages of the embryo inside the capsules during the incubation period is understood.

[ Key words: Sepioteuthis lessoniana , intercapsular development ]

There are about 660 species of cephalopods in the world oceans, of which less than hundred species are of commercial importance. In the Indian seas, about 80 species of cephalopods exist but the main fishery is contributed by only a dozen or so. Though they play an important role in the economy of our country, their early life cycle and reproductive biology are not yet understood clearly. In the global cephalopod catch, Squids dominate by 77% followed by octopus and cuttlefish1. In India, the big fin squid is high valued seafood next to the Pharaoh cuttlefish. Sepia pharaonis and is abundant in the coastal waters of the east coast of India. This study mainly focuses on the embryonic development of big fin squid Sepioteuthis lessoniana Lesson inside the capsules till hatching out of the fully developed paralarva from the eggs. Pre-sent study was carried out with the aim of culturing this commercially important cuttle fish under the laboratory condition.

Wild spawned egg masses of big fin squid, Sepio-teuthis lessoniana were collected from nylon net pieces, which were set at a depth of 5 feet. The depos-ited egg masses were transferred to the laboratory and kept in glass aquaria measuring 12″ × 6″ × 12″ con-taining filtered seawater. Sixty percent of water in the tank was exchanged daily. The glass aquarium was covered with black chart paper to avoid the growth of algae, which may lead to the formation of a pale green colouration on the surface of the capsule leading to

the death of the embryo. Egg capsules were taken everyday to study the developmental stages of the growing embryos. Size of the egg capsules, eggs and the embryos inside the eggs were recorded everyday till hatching. Various stages of development were ob-served and recorded as line drawings and photographs with the help of a light microscope.

The total incubation period of the big fin squid Sepioteuthis lessoniana varied between 18-20 days. From the first day the egg capsules gradually became enlarged by absorbing water. Unfertilized eggs had a milky white colouration and were removed immedi-ately by visual examination. The average initial length and width of the egg capsules were 58.2 and 12.6 mm respectively and the eggs measured 3 mm. Cleavage, cell division and segregation took place in the first three days of incubation and the embryo measured 2 mm in size. On the day before hatching, the capsules measured 82.4 mm × 14.6 mm while the average size of the eggs and the developing embryos were 16 and 11 mm respectively (Table 1). The incubation period of the eggs of squids and cuttle fish varied with the species. In the case of Thai pygmy squid Idiosepius thailandicus, the incubation and embryonic develop-ment has been studied in detail and the incubation3 period was reported as 12 days. In spineless cuttle fish Sepiella inermis, it was 8-19 days with an average of 12.6 + 4.1 days and incubation period mostly depended on temperature. Low temperature prolonged

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the incubation period but normally the incubation last for 3 weeks3. The incubation period of the eggs of S.lessoniana in Thailand4 varied between 20.2+2.6 days while in Indonesia5 it was 15-16 days. In the present study, the incubation time recorded was 18 days.

The embryonic development is illustrated in the Figs 1 and 2. The developmental changes are ex-plained based on the morphological changes of the developing embryo. On the first day, the cleavage was completed and the germ layers were found segregated with the growth of blastoderm. The blastoderm could be seen as a ring at the vegetal pole covering three quarters of the egg on the second day. In the case of Thai pygmy squid, only the enlargement of the blas-toderm has been explained2. Sakai6 has schematically explained the ring formation of the blastopore at 53 hours after fertilization in Illex argentinus. Between third and fifth day, organogenesis began from the in-vagination and the mantle was visible in S. lesson-iana. In the case of Thai pygmy squid, organogenesis took place after 5 days of fertilization with the forma-tion of eye, mantle and rotation of the embryo2 while in the Argentine squid, Illex argentinus6 it was 112 hours.

Table 1 ⎯ The average size of the egg capsules, eggs and the growing embryos during the developmental period

No. of Average size of the Mean size of the Mean size of thedays egg capsules eggs (mm) embryos (mm) (length × width) mm

1 158.2 × 12.6 3 ⎯ 2 263.3 × 14.0 3 ⎯ 3 55.6 × 12.5 3 ⎯ 4 61.3 × 13.2 5 2 5 61.7 × 12.6 8 5 6 58.3 × 12.3 9 5 7 63.2 × 12.4 10 7 8 69.6 × 12.7 10 7 9 69.0 × 12.8 12 8 10 74.1 × 14.6 15 8 11 74.7 × 15.5 15 10 12 78.3 × 15.4 15 12 13 84.0 × 15.2 16 12 14 86.3 × 15.8 16 9 15 82.7 × 15.5 16 9 16 82.3 × 15.3 16 8 17 82.2 × 15.3 16 9 18 82.4 × 15.0 16 11

Fig. 1 ⎯ Embryo stages of day 5 to 17

Fig 2 ⎯ Embryo development stages (BD – Blastodisc , CH – Chorion, EY – Eye , ML – Mantle, SG – Shell gland, AR – Arm, TE – Tentacle, FL – Funnel, SP – Sucker Primordia, CH – Chromatophores, FN – Fin , GL – Gill , IS – Ink sac ,YO – Yolk, AR 1 – Arm 1, AR 2 – Arm 2 , AR 4 – Arm 4)

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In S. lessoniana, the mantle started widening on the sixth day. Ocular cups and eyes were evident on the seventh day. The respiratory movements were clear and the mantle length increased occupying one third of the total length on the eighth day. The yolk started to decrease gradually from the eighth day and the size of the eggs and the embryos increased on the ninth day. In ten days old embryo, the tentacles were prominent with the sucker primordia on the tip and on the eleventh day, the fins started to appear. Ink gland was visible inside the thin transparent mantle. Chro-matophores on the body were clear on the twelfth day but very pale in colouration. While in other squids such as Illex argentinus and Idiosepius thailandicus the chromatopores were found visible after 150 hours and 10th day respectively. The members of the class cephalopoda are noted for their chromatophores, which help them to camaflouge with their substrate and to escape from predators for defense or to hunt for their prey. From thirteenth to seventeenth day, the yolk totally reduced and the organs of the embryo were fully developed. Decreasing of yolk is another character to confirm the development of embryo. The paralarvae having little yolk sometime hatched out with the yolk due to mechanical shock and after a few minutes of vigorous swimming, dropped the yolk and started swimming freely. Alagarswami7 noticed that in Sepioteuthis arctipinnis (=Sepioteuthis lessoniana ) the yolk sac was found to be carried along with the embryo to outside for some hatchlings and discarded after an hour. However in the present study the paralrvae of this kind usually did not survive for long and were susceptible to bacterial infection. The size of the embryo started decreasing from 14th day due to the reduction of the yolk size as the developing embryo

absorbed it. The egg size maintained at 16 mm from day 13 onwards till the paralarva hatched out. On eighteenth day, the paralarva hatched out and it was 6 mm in size (Dorsal Mantle Length). The fins were functional and the ink sac was active if there was any mechanical disturbance.

The present study will be a base for knowing the developmental stages, incubation and hatching out of paralarvae for the big fin squid Sepioteuthis lesson-iana, to do further culture studies.

Authors are grateful to Dr. Jorgen Hylleberg, Pro-gram Director for the financial assistance to carry out this work through Tropical Marine Mollusc Pro-gramme (TMMP) project, DANIDA.

References 1 Josupiet H, A change of direction for cephalopod consumption,

Seafood Internatl, (2001) 25-27. 2 Nabhitabhatta J, Life cycle of the cultured big fin squid Sepio-

teuthis lessoniana Lesson, Phuket Mar Biol Cen Spe Pub No 16, (1996) 83-95.

3 Danakusumah E, Studies on the biology and culture of the neritic squid Sepioteuthis lessoniana Lesson : Effects of stock-ing density on survival rate, Phuket Mar Biol Cen Spe Pub No. 19, (1999) 223-226.

4 Nabhitabhatta J, Distinctive behaviour of the Thai pygmy squid, Idiosepius thailandicus Chotiyaputta, Okutani and Chai-tiamvong,1991, Phuket Mar Biol Cen Spe Pub No.18, (1998) 25-40.

5 Nabhitabhatta J, Life cycle of three cultured generations of spineless cuttle fish, Sepiella inermis (Ferussac & D’orbingy) Phuket Mar Biol Cen Spel Pub No17, (1997) 289-298.

6 Sakai M, Brunetti N E, Elana & Sakurai Y, Embryonic devel-opment and hatchlings of Illex argentinus derived from artifi-cial fertilization. Cephalopod Biodiversity, Ecology and Evolu-tion, S. Afr J Mar Sci, 20 (1996) 255-265.

7 Alagarswami K, On the embryonic development of the squid (Sepioteuthis arctipinnis Gould) from the Gulf of Mannar, J Mar Bio Ass India, 8 (1966) 278-284.