Post by Ismail AbdulAzeez on Dec 25, 2013 23:00:36 GMT 1
ABSTRACT
Sixty sexually mature purebred black-skinned Archachatina marginata snails with weight rang- ing from 120.50 g to 135.70 g were used to gen- erate eggs in this study. The eggs collected were incubated in a chamber filled with loamy soil for appropriate observation and assessment (crac- king at four days intervals to check snailet’s development). Results obtained from the study showed that at laying snail egg weights ranged from 1.54 - 2.45 g (mean of 2.00 g). The egg lengths and widths ranged from 13.50 - 16.90 mm (mean of 15.20 mm) and 10.00 - 12.70 mm (mean of 11.40 mm) respectively. The results also revealed that at laying (day one) the egg content was translucent or clear (blank) when observed with light from a powered microscope. Observation of eggs on day four showed the for- mation of embryo with a semi-transparent cup attached to a long string body. On day 12, some specific organs of the snailet had developed, and there was a reduction in the liquid content. On day 28, the snailet was fully formed, but the shell still contained very small volume of liquid.
The snailet hatched on day 29.
Keywords: Development; Quality; Traits; Eggs; Snail; Stages
1. INTRODUCTION
Archachatina marginata is the second largest gastro- pod among the giant African land snails [1,2], but the most popular breed of snail is kept and reared in Nigeria. Snails have high rate of prolific fecundity compared with other livestock and are capable of continuous egg laying several times over a period after a single mating. Refer- ence [3] opined that snails can start to lay eggs when they are sexually mature at 8 - 12 months or when their body weight is between 110 g and 125 g. On the other hand, [4] opined that the body weight of mature snails A. marginata (S) ranges from 120 g to 140 g, while [5] not- ed that body weight of mature A. marginata ranges from 226.22 g to 237 g for black-skinned ectotype and from 57.54 g to 67.07 g for white-skinned ectotype.
Although, snails are hermaphrodites, they practice se- xual reproduction [6,7]. Moreso, [7-9] opined that snails are very choosy in their mating partners and sometimes are uninterested in mating with other snails of the same species originating from a considerable distance away. Snails lay 4 - 18 eggs in 1 - 2 minutes [8,10] unlike hens that lay one egg per day. Reference [11] observed that A. marginata lays 5 - 11 eggs within the same period (1 - 2 minutes). Reference [12] described the egg as being spherical and cream yellow in color, while [13] described the eggs as being chalky white. On the other hand, [7] opined that the eggs of A. marginata are spherical, trans- lucent and yellowish in color.
Reference [10] gave the average egg weights of the black and white skinned ectotypes of A. marginata to be 1.80 g and 1.05 g respectively. The mean egg lengths for black-skinned and white-skinned ectotypes of A. margi- nata reported by [10] were 1.61 mm and 1.43 mm re- spectively. Besides, the same authors had earlier given very low mean width values of 1.29 mm and 1.05 mm for the black-skinned and white-skinned ectotypes of A. marginata respectively.
Copyright © 2013 SciRes. OPEN ACCESS
Reference [14] opined that embryonic development is a ceaseless process till eclosion, which involves several aspects such as zygote metabolism, cleavage, blastula- tion, gastrulation and organogenesis. The morphological and behavioral aspects of development of fresh water snail have been well documented [15]. Besides, [16-18] have also described the reproduction and embryology of the different species of Lymnaea.
While there is the paucity of information on the deve- lopmental stages of the land snails, this research seeks to find out the different important stages of embryonic de- velopment of A. marginata snails. The knowledge of op- timal conditions for successful embryonic development will be useful for biochemical and cytological studies of early development in A. marginata for achieving maxi- mal productivity in snail hatcheries, as well as for gene- tic manipulation.
2. MATERIALS AND METHODS
The research was carried out at the Snailery Unit of Animal Science Department, University of Uyo, Uyo, Nigeria. The snailery provided micro-environment simi- lar to the natural habitat of snails as it is planted with mango trees and tall grasses which provided shades and protected the hutches from direct sunlight and heavy rainfall. Uyo, the capital of AkwaIbom State, is situated between Latitude 4˚31′ N and 4˚45′ N, Longitude 7˚31′ E and 4˚45′ E with mean temperature of 30˚C and rainfall of 2000 - 3000 mm per annum [19,20].
Sixty sexually mature purebred black-skinned A. mar- ginata snails (Figure 1) of mean fresh body weight range from 120.50 g to 135.70 g purchased from a local market (Itam) in Uyo metropolis were used for the study. The description of the selection, management of the snails and breeding (natural mating) pattern were as prescribed in [9,21].
The fertile, fresh eggs were collected at lay, on the first day usually in the morning after carefully searching through the soil and under the potato leaves in the hut- ches. The eggs (Figure 2) were taken to the laboratory and were carefully cleansed of adhering soil, sorted
Figure 1. Black skinned Archachat- ina marginata (S) snail.
Copyright © 2013 SciRes.
against cracks and morphological abnormalities, weighed and external parameters (length and width) measured. The eggs were then placed in an incubation chamber filled with loamy soil and maintained at moderate soil tempe- rature range from 25˚C to 29˚C, relative humidity range from 70% - 80% for proper development of the snail eggs. The eggs were turned during measurements. The eggs were later removed from the soil and cracked at four (4) days interval to study their developmental stages. Pho- tographs of the developmental stages were taken (Figur- es 3-10).
Data collected were number of eggs laid as counted, egg weight (g), egg length (mm) and egg width (mm). An electronic balance, ScoutTM pro scale with 0.01 g to 1000 g sensitivity was used to measure egg weight, while Vernier Caliper was used to measure length and width. The egg traits were analyzed using simple statistics.
3. RESULTS AND DISCUSSION
The results of egg traits at lay are presented in Table 1.
Figure 2. Translucent (clear) eggs of A. mar- ginata at lay (1st day).
Figure 3. Embryo formation (4th day).
1123
Figure 7. Edible part (foot) is complete-
ly buried in a large volume of egg fluid Figure 4. Full cell formation without special- (20th day). ized organs (8th day).
Figure 5. Organs were seen as intestinal body
moved into the shell and the foot hanged out Figure 8. Volume of egg liquid became rela-
(12th day). tively reduced while shell colour became
th dark brown (24 day).
Figure 6. Complete condensation of the body Figure 9. Snailet was fully developed parts into the shell (16th day). but with a very little volume of egg fluid (28th day).
The mean egg weight at lay of 2.00 g, range (1.54 - 2.45
g) obtained in the study is quite higher than the mean egg approached hatchling date. This, [9] opined are due to weight values reported in [10,21] for A. marginata. How- changes in the egg liquid mass to baby snail during the ever, the mean egg weight decreased with age as the egg embryonic development as well as the baby snail feeding Copyright © 2013 SciRes.
Figure 10. Actual hatching of eggs as- snailets crawled out of their shells (29th day).
Table 1. Egg quality traits of black-skinned Archachatina mar- ginata (S) snails.
Traits Mean values/Range
Egg weight (g) at lay 2.00 (1.54 - 2.45)
Egg length (mm) at lay 15.20 (13.50 - 16.90)
Egg width (mm) at lay 11.40 (10.00 - 12.70)
Egg shape and colour at lay Spherical and yellow
on the liquid mass, thus making the egg lighter.
The shape and colour of the eggs obtained in this stu- dy was spherical and yellow. These agreed with the ob- servations of [7,12].
The developmental stages of snail eggs are shown on Figures 3-10. The egg content on the first day of obser- vation at lay was clear (blank) or translucent. No struc- ture was observed with the light powered microscope. This result agreed with the views of [7] of the snail egg being translucent (clear) at lay.
On the 4th day of incubation, embryo formation was observed as a semi-transparent cup attached to a long string body (Figure 3). This structure was quite similar to the embryo observed by [22] for L. acuminate (fresh water) snail. These authors reported that the embryo at this stage took an elongated shape, with the development of mouth, velum or prototroch and head vesicle. On the 8th day, the embryonic development continued with full cell formation but with no specialized organ formed. There was also additional condensation of the intestine as the embryo separated from the yolk as observed in the shell (Figure 4).
There were dramatic changes observed on the 12th day. The intestinal body moved into the shell and the edible part (foot) was seen hanging out of the shell. A dispatch part was also seen in the snail fluid with mantle and other developed organs of the body shown (Figure 5). The
Copyright © 2013 SciRes.
heart was physically well observed, with 43 heart beat counted per minute. This observation was quite similar to that reported by [22] at the sixth (6th) day of incubation. The authors noted that at veliger state, the L. acuminate head, foot region sharply became demarcated from the visceral mass with a pair of tentacles bearing darkly pig- mented eyes at their bases. On the 16th day, there was complete condensation of the body part into the shell bearing the mantle. The shell colour which was transpa- rent now took up a yellowish colour. It was also observed that the egg still contained a large volume of liquid out- side the snailet of the snail’s egg (Figure 6). This agreed with [23] the observations of large fluid volume.
On the 20th day, the edible part of the snail was clearly buried in a large volume of egg fluid as on day 16th. The colour of the shell became dark yellow, while the edible part had a milky colour (Figure 7). On the 24th day, the colour of the shell became dark brown and the volume of egg liquid was relatively reduced (Figure 8).
On the 28th day, the young snailet was fully developed but with a very small volume of egg liquid upon which the snailet was observed crawling ( Figure 9). The actual hatching took place on 29th day when the egg shell broke naturally and the snailet crawled out of the shell (Figure 10).
The results of the developmental stages and timing of 29 days obtained in this study confirmed mean incuba- tion period of 29 days, (ranged 28 - 30 days). This result agreed with [21] incubation period report of 29.54 ± 1.48 days for black-skinned purebred A. marginata, but higher than [24] reported value of 14 - 21 days. Stievenant [25] reported values of 14 - 28 days for A. marginata snail.
Reference [26] and [12] reported that incubation period for black-skinned A. marginata ranged between 29 and 32 days. Whereas [8] gave a slightly higher incubation period range of 25 - 32 days. The disparity in incubation period may be attributed to variation in genetic factors like breed, strain, age and size of the snail, egg size and environmental factors like temperature and relative hu- midity. Besides, [21] opined that exposure of eggs to flu- ctuating environmental conditions which differed from their near constant uterine environment may influence or increase incubation period. In addition, [21,27] noted that incubation conditions such as uptake and loss of mois- ture and increased transpirational water loss resulting from increased heat produced by the developing embryo can also cause this variation.
4. CONCLUSION
The mean egg weight (2.00 g), egg length (15.20 mm) and egg width (11.40 mm) for giant African land snail, Archachatina marginata (S) and the 29 days incubation period obtained depended on genetic and environmental factors governing the snail and the environment of the study. The shape and color of the eggs are spherical and yellow. The embryonic developmental stages on four (4) days interval for Archachatina marginata snail confirm- ed that the snail hatched between 28 and 30 days with mean incubation period of 29 days. The observations made in this study have opened a new avenue for future workers to establish developmental mechanism and snail culture farms.
5. RECOMMENDATION
It is however highly recommended that in-depth stud- ies on developmental stages of giant African land snail eggs probably using scanning method with two (2) days interval should be carried out. This will give detailed structures and organs of each developmental stage which will help the snail breeders in morphological, biochemi- cal, cytological and behavioral studies as well as genetic manipulation of embryonic development in Archachatina marginata snails.
REFERENCES
[1] CAB (2003) Crop protection compendium: Global mod- ule. Commonwealth Agricultural Bureau International, Wallingford.
[2] Venette, R.C. and Larson, M. (2004) Mini risk assessment giant Africant snail, Achatinafulica (Bowdich) [Gastropo- da: Achatinidae]. Department of Entomology, University of Minnesita, St. Paul, 1-30.
[3] Omole, A.J., Twaiwo, A.A. and Amusan, J.A. (2007) Te- chnical guide/bulletin. Practical snail farming. Ibadan, Ni- geria. Institute of Agricultural Research and Training, Moor Plantation, 26.
[4] Ebenso, I.E. (2003) Nutritive potential of white snail (Archachatinamarginata) in Nigeria. Discovery Innova- tion, 15, 156-158.
[5] Okon, B., Ibom, L.A., Etuk, N.E. and Akpan, E.W. (2008) Variations in growth patterns and conformation of snail. Influence of strain and location on isometry of growth in Cross River State, Nigeria. Journal of Agriculture, For- estry and the Social Sciences (JOAFSS), 6, 218-226.
[6] Akinnusi, O. (2004) Introduction to snails and snail farm- ing. 2nd Edition, Abeokuta, Nigeria, Triolas Exquisite Ven- tures, 90.
[7] Okon, B. and Ibom, L.A. (2012) Snail breeding and snai- lery management. Freshdew Productions, Calabar, 1-70.
[8] Omole, A.J. and Kehinde, A.S. (2005) Backyard snail farming at a glance. Back to Agricultural Series (1) Iba- dan Technovisor Agricultural Publications.
[9] Ibom, L.A. (2009) Variations in reproductive and growth performance trait of white-skinned x black-skinned Afri- can giant snail hatchlings [Archachatinamarginata (Swain- son)] in Obubra, Nigeria. Ph.D. Thesis, Department of Animal Science, University of Calabar, Calabar, 166. [10] Ibom, L.A., Okon, B. and Essien, A. (2008) Morphomet-
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ric analysis of eggs laid by two ectotypes of snails Archa- chatinamarganata (Swainson) raised in captivity. Global Journal of Agricultural Sciences, 7, 119-121.
[11] Akinnusi, O. (1999) Introduction to snails and snail farm- ing. Triolas Exquisite Ventures, Abeokuta.
[12] Ogogo, A.U. (2004) Wildlife management in Nigeria. Ob- jectives, principles and procedures. Median Communica- tions, Calabar, 134-154.
[13] Raut, S.K. and Barker, G.M. (2002) Achatina fulica Bon- dich and other Achatinidae as pests in tropical agriculture. In: Barker G.M., Ed., Molluscs as Crop Pests, CABI Pub- lishing, Hamilton, 55-114. dx.doi.org/10.1079/9780851993201.0055
[14] Bhramachery, A. (1992) Embryonic development of snail. www.rirdcgov.au.
[15] Morril, J.B. (1982) Development of Pulmonate Gastropod, Lymnaea. In: Harrison, F.W. and Cowden, R.R., Eds., De- velopmental Biology of Fresh Water Invertebratesliss, Mc Grad Hill, New York, 399-483.
[16] Pressing, M. (1993) Influence of an insecticide K-othrine on the reproduction and mortality of the pond snail (Lym- naeastagnalis L.). Archives of Environmental Contamina- tion and Toxicology, 25, 387-393.
[17] Herman, P.M., Meat, A. and Jansen, R.F. (1994) The neu- tral control of egg laying in the pond snail. Lymnaeastag- nalis, mito control of shell turning. Journal of Experi- mental Biology, 197, 79-99.
[18] Roudeland, D. and Dreyfuss, G. (1996) The development of tissue lesions in the snail Lymnaea glabra exposed to a sublethal dose of molluscide. Verterinary Research, 27, 79-86.
[19] Udosen, C. (2000) Application of remote sensing and GIS techniques in terrain mapping and watershed management. In: Yang, S., Ed., South-Eastern Nigeria: It’s Environment, Abaam Publishing, Uyo, 23-28.
[20] Ebenso, I., Ekwere, A., Akpan, B., Okon, B., Inyang, U. and Ebenso, G. (2012) Occurrence of Salmonella, Vibro and E. coli in edible land snail in Niger Delta, Nigeria. Journal of Microbiology, Biotechnology and Food Sci- ences, 2, 610-618.
[21] Ibom, L.A., Okon, B. and Bassey, B.E.E. (2012) Egg traits, hatchability and survivability of black-skinned, white skin- ned and crossbred Archachatina marginata snails. Inter- national Journal of Agricultural Science and Bioresource Engineering Research, 1, 10-18.
[22] Md. Moniruzzanam, S., Badrun, N. and Md. Sarwar, J.
(2007) Embryonic development ecology of fresh water snail Lymnaeae acuminate (Lymnaidae: Gastropoda) Pa- kistan Journal of Biological Sciences, 10, 23-31.
dx.doi.org/10.3923/pjbs.2007.23.31
[23] Demian, E.S. and Yousif, F. (1975) Embryonic develop- ment and organogenesis in the snail Marisa cornuaristic (Mesogastropoda anpullaridae). Malacologia, 15, 29-42.
[24] Cobbinah, J.R. (1993) Snail farming in West Africa. A practical guide. Sayee Publication, CTA Publication.
[25] Stievenant, C. (1996) Shell morphology, growth repro- duction and aestivation by African snails. Laboratory ob- servations on Archachatina marginata Saturalis, Achati-
naachatina and Achatinafulica. Ph.D. Thesis, University University of Ibadan, Ibadan.
of Ibadan, Ibadan, 206. [27] Tracy, C.R., Packard, G.C. and Packard, M.J. (1978) Wa-
[26] Awesu, M.O. (1980) The biology and management of the ter relations of chelonian eggs. Physiological Zoology, 51, African giant land snail (A. marginata). M. Phil. Thesis, 378-387.
Source: dx.doi.org/10.4236/ns.2013.510137
Sixty sexually mature purebred black-skinned Archachatina marginata snails with weight rang- ing from 120.50 g to 135.70 g were used to gen- erate eggs in this study. The eggs collected were incubated in a chamber filled with loamy soil for appropriate observation and assessment (crac- king at four days intervals to check snailet’s development). Results obtained from the study showed that at laying snail egg weights ranged from 1.54 - 2.45 g (mean of 2.00 g). The egg lengths and widths ranged from 13.50 - 16.90 mm (mean of 15.20 mm) and 10.00 - 12.70 mm (mean of 11.40 mm) respectively. The results also revealed that at laying (day one) the egg content was translucent or clear (blank) when observed with light from a powered microscope. Observation of eggs on day four showed the for- mation of embryo with a semi-transparent cup attached to a long string body. On day 12, some specific organs of the snailet had developed, and there was a reduction in the liquid content. On day 28, the snailet was fully formed, but the shell still contained very small volume of liquid.
The snailet hatched on day 29.
Keywords: Development; Quality; Traits; Eggs; Snail; Stages
1. INTRODUCTION
Archachatina marginata is the second largest gastro- pod among the giant African land snails [1,2], but the most popular breed of snail is kept and reared in Nigeria. Snails have high rate of prolific fecundity compared with other livestock and are capable of continuous egg laying several times over a period after a single mating. Refer- ence [3] opined that snails can start to lay eggs when they are sexually mature at 8 - 12 months or when their body weight is between 110 g and 125 g. On the other hand, [4] opined that the body weight of mature snails A. marginata (S) ranges from 120 g to 140 g, while [5] not- ed that body weight of mature A. marginata ranges from 226.22 g to 237 g for black-skinned ectotype and from 57.54 g to 67.07 g for white-skinned ectotype.
Although, snails are hermaphrodites, they practice se- xual reproduction [6,7]. Moreso, [7-9] opined that snails are very choosy in their mating partners and sometimes are uninterested in mating with other snails of the same species originating from a considerable distance away. Snails lay 4 - 18 eggs in 1 - 2 minutes [8,10] unlike hens that lay one egg per day. Reference [11] observed that A. marginata lays 5 - 11 eggs within the same period (1 - 2 minutes). Reference [12] described the egg as being spherical and cream yellow in color, while [13] described the eggs as being chalky white. On the other hand, [7] opined that the eggs of A. marginata are spherical, trans- lucent and yellowish in color.
Reference [10] gave the average egg weights of the black and white skinned ectotypes of A. marginata to be 1.80 g and 1.05 g respectively. The mean egg lengths for black-skinned and white-skinned ectotypes of A. margi- nata reported by [10] were 1.61 mm and 1.43 mm re- spectively. Besides, the same authors had earlier given very low mean width values of 1.29 mm and 1.05 mm for the black-skinned and white-skinned ectotypes of A. marginata respectively.
Copyright © 2013 SciRes. OPEN ACCESS
Reference [14] opined that embryonic development is a ceaseless process till eclosion, which involves several aspects such as zygote metabolism, cleavage, blastula- tion, gastrulation and organogenesis. The morphological and behavioral aspects of development of fresh water snail have been well documented [15]. Besides, [16-18] have also described the reproduction and embryology of the different species of Lymnaea.
While there is the paucity of information on the deve- lopmental stages of the land snails, this research seeks to find out the different important stages of embryonic de- velopment of A. marginata snails. The knowledge of op- timal conditions for successful embryonic development will be useful for biochemical and cytological studies of early development in A. marginata for achieving maxi- mal productivity in snail hatcheries, as well as for gene- tic manipulation.
2. MATERIALS AND METHODS
The research was carried out at the Snailery Unit of Animal Science Department, University of Uyo, Uyo, Nigeria. The snailery provided micro-environment simi- lar to the natural habitat of snails as it is planted with mango trees and tall grasses which provided shades and protected the hutches from direct sunlight and heavy rainfall. Uyo, the capital of AkwaIbom State, is situated between Latitude 4˚31′ N and 4˚45′ N, Longitude 7˚31′ E and 4˚45′ E with mean temperature of 30˚C and rainfall of 2000 - 3000 mm per annum [19,20].
Sixty sexually mature purebred black-skinned A. mar- ginata snails (Figure 1) of mean fresh body weight range from 120.50 g to 135.70 g purchased from a local market (Itam) in Uyo metropolis were used for the study. The description of the selection, management of the snails and breeding (natural mating) pattern were as prescribed in [9,21].
The fertile, fresh eggs were collected at lay, on the first day usually in the morning after carefully searching through the soil and under the potato leaves in the hut- ches. The eggs (Figure 2) were taken to the laboratory and were carefully cleansed of adhering soil, sorted
Figure 1. Black skinned Archachat- ina marginata (S) snail.
Copyright © 2013 SciRes.
against cracks and morphological abnormalities, weighed and external parameters (length and width) measured. The eggs were then placed in an incubation chamber filled with loamy soil and maintained at moderate soil tempe- rature range from 25˚C to 29˚C, relative humidity range from 70% - 80% for proper development of the snail eggs. The eggs were turned during measurements. The eggs were later removed from the soil and cracked at four (4) days interval to study their developmental stages. Pho- tographs of the developmental stages were taken (Figur- es 3-10).
Data collected were number of eggs laid as counted, egg weight (g), egg length (mm) and egg width (mm). An electronic balance, ScoutTM pro scale with 0.01 g to 1000 g sensitivity was used to measure egg weight, while Vernier Caliper was used to measure length and width. The egg traits were analyzed using simple statistics.
3. RESULTS AND DISCUSSION
The results of egg traits at lay are presented in Table 1.
Figure 2. Translucent (clear) eggs of A. mar- ginata at lay (1st day).
Figure 3. Embryo formation (4th day).
1123
Figure 7. Edible part (foot) is complete-
ly buried in a large volume of egg fluid Figure 4. Full cell formation without special- (20th day). ized organs (8th day).
Figure 5. Organs were seen as intestinal body
moved into the shell and the foot hanged out Figure 8. Volume of egg liquid became rela-
(12th day). tively reduced while shell colour became
th dark brown (24 day).
Figure 6. Complete condensation of the body Figure 9. Snailet was fully developed parts into the shell (16th day). but with a very little volume of egg fluid (28th day).
The mean egg weight at lay of 2.00 g, range (1.54 - 2.45
g) obtained in the study is quite higher than the mean egg approached hatchling date. This, [9] opined are due to weight values reported in [10,21] for A. marginata. How- changes in the egg liquid mass to baby snail during the ever, the mean egg weight decreased with age as the egg embryonic development as well as the baby snail feeding Copyright © 2013 SciRes.
Figure 10. Actual hatching of eggs as- snailets crawled out of their shells (29th day).
Table 1. Egg quality traits of black-skinned Archachatina mar- ginata (S) snails.
Traits Mean values/Range
Egg weight (g) at lay 2.00 (1.54 - 2.45)
Egg length (mm) at lay 15.20 (13.50 - 16.90)
Egg width (mm) at lay 11.40 (10.00 - 12.70)
Egg shape and colour at lay Spherical and yellow
on the liquid mass, thus making the egg lighter.
The shape and colour of the eggs obtained in this stu- dy was spherical and yellow. These agreed with the ob- servations of [7,12].
The developmental stages of snail eggs are shown on Figures 3-10. The egg content on the first day of obser- vation at lay was clear (blank) or translucent. No struc- ture was observed with the light powered microscope. This result agreed with the views of [7] of the snail egg being translucent (clear) at lay.
On the 4th day of incubation, embryo formation was observed as a semi-transparent cup attached to a long string body (Figure 3). This structure was quite similar to the embryo observed by [22] for L. acuminate (fresh water) snail. These authors reported that the embryo at this stage took an elongated shape, with the development of mouth, velum or prototroch and head vesicle. On the 8th day, the embryonic development continued with full cell formation but with no specialized organ formed. There was also additional condensation of the intestine as the embryo separated from the yolk as observed in the shell (Figure 4).
There were dramatic changes observed on the 12th day. The intestinal body moved into the shell and the edible part (foot) was seen hanging out of the shell. A dispatch part was also seen in the snail fluid with mantle and other developed organs of the body shown (Figure 5). The
Copyright © 2013 SciRes.
heart was physically well observed, with 43 heart beat counted per minute. This observation was quite similar to that reported by [22] at the sixth (6th) day of incubation. The authors noted that at veliger state, the L. acuminate head, foot region sharply became demarcated from the visceral mass with a pair of tentacles bearing darkly pig- mented eyes at their bases. On the 16th day, there was complete condensation of the body part into the shell bearing the mantle. The shell colour which was transpa- rent now took up a yellowish colour. It was also observed that the egg still contained a large volume of liquid out- side the snailet of the snail’s egg (Figure 6). This agreed with [23] the observations of large fluid volume.
On the 20th day, the edible part of the snail was clearly buried in a large volume of egg fluid as on day 16th. The colour of the shell became dark yellow, while the edible part had a milky colour (Figure 7). On the 24th day, the colour of the shell became dark brown and the volume of egg liquid was relatively reduced (Figure 8).
On the 28th day, the young snailet was fully developed but with a very small volume of egg liquid upon which the snailet was observed crawling ( Figure 9). The actual hatching took place on 29th day when the egg shell broke naturally and the snailet crawled out of the shell (Figure 10).
The results of the developmental stages and timing of 29 days obtained in this study confirmed mean incuba- tion period of 29 days, (ranged 28 - 30 days). This result agreed with [21] incubation period report of 29.54 ± 1.48 days for black-skinned purebred A. marginata, but higher than [24] reported value of 14 - 21 days. Stievenant [25] reported values of 14 - 28 days for A. marginata snail.
Reference [26] and [12] reported that incubation period for black-skinned A. marginata ranged between 29 and 32 days. Whereas [8] gave a slightly higher incubation period range of 25 - 32 days. The disparity in incubation period may be attributed to variation in genetic factors like breed, strain, age and size of the snail, egg size and environmental factors like temperature and relative hu- midity. Besides, [21] opined that exposure of eggs to flu- ctuating environmental conditions which differed from their near constant uterine environment may influence or increase incubation period. In addition, [21,27] noted that incubation conditions such as uptake and loss of mois- ture and increased transpirational water loss resulting from increased heat produced by the developing embryo can also cause this variation.
4. CONCLUSION
The mean egg weight (2.00 g), egg length (15.20 mm) and egg width (11.40 mm) for giant African land snail, Archachatina marginata (S) and the 29 days incubation period obtained depended on genetic and environmental factors governing the snail and the environment of the study. The shape and color of the eggs are spherical and yellow. The embryonic developmental stages on four (4) days interval for Archachatina marginata snail confirm- ed that the snail hatched between 28 and 30 days with mean incubation period of 29 days. The observations made in this study have opened a new avenue for future workers to establish developmental mechanism and snail culture farms.
5. RECOMMENDATION
It is however highly recommended that in-depth stud- ies on developmental stages of giant African land snail eggs probably using scanning method with two (2) days interval should be carried out. This will give detailed structures and organs of each developmental stage which will help the snail breeders in morphological, biochemi- cal, cytological and behavioral studies as well as genetic manipulation of embryonic development in Archachatina marginata snails.
REFERENCES
[1] CAB (2003) Crop protection compendium: Global mod- ule. Commonwealth Agricultural Bureau International, Wallingford.
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Source: dx.doi.org/10.4236/ns.2013.510137