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Embryonic Developmental Ecology of Freshwater Snail Lymnaea Acuminata (lymnaeidae: Gastropoda)

Md. Moniruzzaman Sarker
Department of Zoology, University of Rajshahi, Bangladesh; University of Ryukyus, Okinawa 903-0213, Japan

Badrun Nesa
University of Ryukyus, Okinawa 903-0213, Japan

Md. Sarwar Jahan
Department of Zoology, University of Rajshahi, Bangladesh

Abstract/ Executive Summary:

The egg type of Lymnaea acuminata was determined as iso-lecithal and the cleavage is spirally holoblastic type. The development of L. acuminata was observed in details. Uncleaved zygote just after laying was found to contain a relatively yolk-free zone, the animal pole and the yolk-rich region, the vegetal pole. No polar bodies were present in eggs examined immediately after they had been laid. The first polar lobe and polar body were extruded out from the zygote within 15-25 min. These were reabsorbed after 12-15 min. The formation of the second polar lobe was followed within the next 48 min. The first cleavage division occurred about 115-130 min after the formation and re-absorption of the second polar lobe, retaining for 7-10 min. The 2-celled embryos underwent the second equal division of cleavage the within next hour and the embryos reached the 4-cell stage. At the end of the 5th h, the 4-celled embryos underwent the third cleavage and the cleavage was horizontal (i.e., equatorial). At the end of the 9th h, the embryos at the 8-celled stage reached the 16-celled stage by the 4th cleavage. The 4th spirally cleaved embryos usually underwent fifth and sixth cleavages within 24-26 and 27-29 h of incubation, respectively. After 2-3 days of incubation, the developing embryos attained the trochophore stage. At the beginning of the 4th day of incubation, embryos became slightly elongated, curved foot muscle and shell gland were developed through the extension of velum and the embryos turned into the early veliger. At the beginning of the seventh day, the miniature snail possessed all the structures found in a newly hatched individual. Interaction between water physico-chemical parameters and some breeding parameters have been observed.

Keywords: Development, Fertlization, Cleavage, Hatchability, Incubation, Trocophore, Veliger

Location: Ecological research laboratory of the Department of Zoology, University of Rajshahi

Start Date: 00-05-2002

End Date: 00-12-2003

Program Area: Animal Health and Management

Commodity: Aquatic animal

Objectives:

To study the sequential events of the embryonic development of L. acuminata with the role played thereon by physico-chemical components like total hardness, magnesium hardness, calcium hardness, pH and dissolve Oxygen of water.

Methodology:

The experiment was conducted at the Ecological research laboratory of the Department of Zoology, University of Rajshahi during the period from May 2002 to December 2003.

In the laboratory a colony of L. acuminata was maintained in filtered, dechlorinated and copper-free tap water (artificial pond water; APW) at 29.57±0.17°C on a 12:12 light: dark cycle. The snails were fed a diet consisting of lettuce, carrot and sweet potato. Aquatic vegetations like Nymphaea, Scirpus, Lemna and Pistia were supplied also for resting and egg laying. To study the embryogenesis and embryokinesis as well as organogenesis of L. acuminata freshly laid egg capsules were collected from the stock culture with the help of a camel hairbrush regularly. The length and width of eggs and developing embryos in the eggs were measured using occulometer in compound microscope (Eagle Instrument Co. Model-180). A batch of 14 freshly land egg capsules were kept separately five glass beakers (500 mL) containing tap water. The experiment was replicated ten times. The developing embryos were studied in vivo with the help of a compound microscope throughout the incubation period and changes were recorded regularly.

Preparation of permanent slide: For preparing permanent slides, eggs incubated for various durations were processed applying the following consecutive procedures: Kept in 50% ethyl alcohol for 30 min, Kept in 70% ethyl alcohol for 40 min, Stained with 1% aqueous solution of Bismark-Brown followed by alcoholic eosin and Mounted with cover slip in D.P.X. Photographs were taken by useing microphotographic apparatus (Model-Leica-III).

Growth: Average geometric growth rates were calculated for two series of developing embryos using the following formula:

Where:

Yo	=	Initial magnitude
Yt	=	Magnitude at time t
t	=	Time measured at intervals of 1 day

Physicochemical properties of water: A total of five sets of experiment were designed for the determination of incubation period and hatchability in respect of physical and chemical parameters of water used for rearing. Physicochemical parameters viz., temperature, pH, dissolved oxygen, total hardness were measured through Hach Kit (Model: FF 1A).

Source of Information: Pakistan Journal of Biological Sciences, 10: 23-31, 2007; ISSN 1028-8880

Article Link (Online Journal): DOI: 10.3923/pjbs.2007.23.31; URL: http://scialert.net/abstract/?doi=pjbs.2007.23.31

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The present study revealed that cleavage would have been completed within 24-26 h of incubation at 29-31°C. The first cleavage division occurred about 115-130 min after the formation of the second polar body. The first division was typical. It passed through the animal-vegetal pole. The two-celled embryos underwent the second equal division of cleavage within the next hour and the embryos reached the 4-celled stage. At the end of 5th h, the 4-celled embryos underwent the third cleavage and the third cleavage was horizontal (i.e., equatorial) which was frequently unequal and produced an upper tier, the micromeres and the lower tier, macromeres.

Knowledge Management: Journal