|Livestock Research for Rural Development 18 (10) 2006||Guidelines to authors||LRRD News||
Citation of this paper
Egg-water flux from gravid Limicolaria aurora in plastic boxes as incubation chambers, under controlled laboratory conditions for 30 days was investigated. Each of 6 incubation chambers with soil as substrate contained 5 eggs each buried in soil differing in water content of control (0), 5, 10, 15, 20 and 25%.
All eggs in control chambers were desiccated. Eggs buried in 15% water incubation chamber hatched. Higher hatchability is assured with increased water uptake after 15 days of incubation.
Key words: Incubation, Limicolaria aurora, snail eggs, water uptake
Edible tropical land snails are small animals, commonly classified as mini-livestock. Opportunity exists to utilize edible snails as nutritious food (Anonymous 2005). Snails contribute as sources of valuable protein, especially for most small-scale farmers in rural areas (Ebenso 2003 ; Paoletti 2005). Edible tropical land snails have become a tool for poverty alleviation of rural dwellers. Snails can also be useful as bio-indicators within their niche. Snails are also easy to domesticate (Ebenso 2005a; Ebenso 2005b; Ebenso et al 2005; Ebenso et al 2006).
Limicolaria aurora is an adichogamus hermaphrodite, producing both sperm and ova from the beginning of maturity. Copulation takes place only at night in a damp environment. For achatinade, each mating pair is distinguished, the initiator as "male behaving" (upper snail), while the acceptor is the "female behaving" (lower snail) (Ebenso et al 2002). Fertilized eggs from gravid snails after oviposition are deposited in "nests" evacuated in the soil. Eggs remain in the "nests" for the entire incubation period. Water is important for successful incubation of snail eggs (Ebenso et al 2004). The incubation period of Limicolaria aurora is 28 - 35 days (Akinnusi 1998).
Presently, there is lack of information on snail egg incubation for rural snail breeders. The objective of this experiment was therefore to investigate effects of water on eggs of Limicolariaaurora incubated in soil under laboratory conditions.
Freshly laid eggs (mass 0.30+ 0.01g) used in this experiment were from gravid Limicolaria aurora (mass 9.39+0.78g, shell length 10.00+0.41cm and shell width 5.37+ 0.42cm), collected locally from rural snail breeders in Uyo, within the wetland ecosystem of guinean forest of Niger Delta, southern Nigeria (rainfall 1500mm and relative humidity 90%). The experiment was carried out in plastic boxes (incubation chambers) measuring 0.15 x 0.15 x 0.65m, with lid tightly covered to reduce evaporation. These chambers were kept in the laboratory under constant condition with a temperature of 26+2oC, and a photoperiod 12 light : 12 darkness, imitating temperature and light conditions comparable to those within the ecosystem.
Loam soil dried to constant temperature of 60oC for 48 h was used as incubation media. Homogenous aliquots of the soil (200g) were placed (up to 3cm) in each chamber with added distilled water at 0 (control), 5, 10, 15, 20 and 25% (g water per 100 g dry soil, weight per weight). 10g of a calcium source (powdered limestone) were mixed into the soil of each treatment. In each incubation chamber, there were 5 eggs each buried in the soil. Eggs were marked with indelible ink for individual egg recognition. Changes in egg mass (nearest 0.01g) was determined at 08 00 h daily. According to Andrews and Sexton (1981), when eggs are removed for weighing, each incubation chamber is also weighed separately, and distilled water added (if mass of chamber together with its content are less than total mass at day 0). Whether water was added or not, the soil in each incubation chamber was stirred thoroughly (with glass rod) to distribute the water in the soil.
Data collection was truncated on day 30 when hatching was first noticed. The control chamber (0%) represented the adverse conditions during the dry season, while 25% water treatment represented wet soil conditions (water saturation) during the rainy season. Data collected were analyzed and interpreted as line graphs, according to Steel et al (1997).
The egg-water flux of incubated Limicolaria aurora eggs at different water concentrations during the experiment period is shown in Figure 1. All eggs in the control incubation chamber became desiccated, an observation in agreement with reports by Ebenso and Solomon (2004) using Archachatina marginata.
Figure 1. Water uptake by incubating eggs.
An egg in 15% chamber (figure 1) hatched on day 30, experimentation was truncated on this day. Tracy et al (1978) studying lizard eggs reported, that heat production by developing embryo might further increase transpiration loss later in the incubation period. In this study, this had to be compensated for by higher water intake. The hatching of an egg in the 15% incubation chamber in this study, agrees with reports of Agbelusi et al (1997) that too much or too little moisture content in the incubation media either prolonged incubation period or prevented hatching.
It may be suggested that eggs of Limicolaria aurora will have the highest water potential after oviposition as compared with reports of Achatina achatina and Archachatina marginata (Ebenso et al 2004). This can be explained with observations of Andrews and Sexton (1981) with reptile eggs, Paganelli et al (1974) with avian eggs, and Sexton et al (1964) with amphibian eggs. These authors concluded that with greater density of fibrils, and a thicker matrix of calcium carbonate, egg shells may provide more resistance to movement of water.
There was increased water uptake above 5% water content (figure 1) in the last 15 days of the experiment period, this agrees with Packard et al (1977), that for normal development of reptilian embryo, the water content of egg apparently must increase during incubation.
Limicolaria aurora eggs cannot survive long period of desiccation, as increased water content of incubation media is necessary from the last 15 days after oviposition.
Rural snail breeders are assured of high snail egg hatchability with application of 15% water content (gram water per gram dry soil, weight per weight) during incubation of snail eggs buried in air tight containers to reduce evaporation.
Agbelusi E A, Adeparusi A and Oluwayemi E 1997 Eggs incubation period and hatching success of African giant snail (Archachatina marginata) in different incubation media. XI World Forestry Congress. Antalya, Turkey.
Akinnusi O 1998 A practical approach to backyard snail farming. Nigerian Journal of Animal Production 25(2): 143 - 147.
Andrews R M and Sexton O J 1981 Water relations of Anolis auratus and Anolis limifrous.Ecology 62 (2): 556 - 562.
Anonymous 2005 The contribution of small animals. In: Small animals in focus. LEISA Magazine. Centre for Information on Low-External Input and Sustainable Agriculture (ILEIA),Bangalore. Sept. 2(3): 4.
Ebenso I E 2003 Dietary calcium supplement for edible tropical land snail Archachatinamarginata in Niger Delta, Nigeria. Livestock Research for Rural Development Volume 15 Article # 5 http://www.cipav.org.co/lrrd/lrrd15/5/eben155.htm
Ebenso I E 2005a Snails caught on the web. Semesterial bulletin of information on mini-livestock. Bureau for Exchange and Distribution of Information on Mini-livestock (BEDIM), Belgium. 14 (2):5-6 http://www.bib.fsagx.ac.be/bedim/production/bulletin/pdf/v14n2.pdf
Ebenso I E 2005b Snails - slowly we are coming out. In: Etim L E, Ndaeyo N U and Obasi O L (eds). Salient Issues in Tropical Agriculture (SITA). A publication of Faculty of Agriculture, University of Uyo, Nigeria. (Accepted).
Ebenso I E, Isaac L J and Obasi O L 2002 Mating behaviour of African giant land snail Archachatina marginata. Nigerian Journal of Forestry 32(2): 72 - 75.
Ebenso I E, Ifut O J, Umoh B I and Udo U H 2004 Water uptake during incubation of egg of Archachatina marginata and Achatina achatina in humid zone. Nigerian Journal of Agriculture, Food and Environment 1(1): 1 - 4.
Ebenso I E, Ita B, Umoren E P, Ita M, Binang W, Edet G, Izah M, Udoh I O, Ibanga G and Ukpong E E 2005 Effect of carbamate molluscicide of African giants snail Limicolariaaurora. Journal of Applied Sciences and Environment Management 9(1): 99 - 102. http://www.bioline.org.br/pdf?ja05018
Ebenso I E, Solomon I P, Inyang D N and Offiong E E A 2006 Anti-nutritional constituents of two edible tropical snails tropical land snails in Nigeria. Global Journal of Pure and Applied Sciences. 12(3): 279-281
Packard G C, Tracy C R and Roth J J 1977 The physiological ecology of reptilian eggs and embryos, and the evolution at viviparity within the class reptilia. Biological Review 52:71 - 105.
Paganelli C V, Olszokwa A and Ar A 1974 The avian egg: surface area, volume and density. Condor 76: 319 - 325.
Paoletti M G (editor) 2005 Ecological implications of mini-livestock-role of insects, rodents, frogs, snails for sustainable development. Science Publishers, London.
Sexton O J, Heatwole H and Knight D 1964 Correlation of micro-distribution of some Panamanian reptiles and amphibians with structural organization of the habitat. Caribbean Journal of Science 4: 261 - 295.
Tracy C R, Packard G and Packard M J 1978 Water relations of Chelonian eggs. Physiological Zoology 51: 378 - 387.
Received 19 February 2006; Accepted 19 July 2006; Published 4 October 2006