Dietary calcium supplement for edible tropical land snails Archachatina marginata in Niger Delta, Nigeria

I E Ebenso

Department of Animal Science, University of Uyo, PMB 1017, Uyo, Nigeria
imeebenso@yahoo.com 

Abstract

Eighty-four (84)  Archachatina marginata hatchlings (mean weight 9+1g) were fed for eight weeks on green fresh chopped Carica papaya fruits ad libitum as control and in combination with five powdered calcium sources from egg shell, limestone, wood-ash, oyster shell, bone meal, at levels of  10, 20, 30 and 40% of diet DM.

The 20% oyster shell dietary supplement gave the best  weight gain

Key words: Archachatina marginata, calcium, Nigeria, snails 

Introduction

Edible tropical land snails are abundant during the wet season, when they are easily gathered especially at night and before dawn. These snails can easily be domesticated and controlled (Ebenso 2002; Ebenso and Okafor 2002; Ebenso 2003a). The consumption of snail meat by rural communities is governed more by culture than by social status (Ebenso 2003b). 

Domesticated snails are three or five times higher in calcium content of their meat than snails from the wild (Lee et al 1994). According to Aboua (1995), Archachatina marginata meat contains 1.41% Ca while the shell contains 0.53% Ca with 36.8 and 0.05% phosphorus respectively. Imevbore and Ademosun (1988) reported that snail meat is particularly rich in Ca and P, which are much lower in beef. 

Most snails consumed in the Niger Delta region of southern Nigeria are gathered from the wild. This area is prone to crude oil pollution. Soils contaminated with crude oil contain reduced exchangeable calcium, thereby becoming acidic (Udo and Fayemi 1975). Snail consumption in this area could lead to calcium deficiency symptoms especially in rural children and pregnant women. 

The adequate rate of calcium mixed in the snail diet is often asked by snail farmers (Stievenart 1992). There is lack of agreement in several studies on dietary calcium in snail farming (Elmslie 1982; Awesu 1988; Olufokunbi et al 1989; Ireland 1991; Awah 1992; Srivastava 1992,;Cobbinah 1994; Monney 1994; Hodasi 1995; Thompson and Cheney 1996). 

The main objective of this study was to determine supplemental dietary calcium levels for edible tropical land snail Archachatina marginata hatchlings gathered from a low soil calcium environment. 

Materials and Methods

Live Archachatina marginata hatchlings with undamaged shells were collected from the wild in Ibeno, a rural area prone to oil spillage in Akwa Ibom State, Niger Delta of southern Nigeria in July. A random selection of 84 snails weighing on average 9+1g were allocated to six quadruplicate treatment groups of four snails. The treatments in a 5*4 factorial arrangement were:

Sources of calcium:

• egg shell, limestone, wood-ash, oyster shell, bone meal

Levels of calcium sources  (% in DM) were:

• 10, 20, 30, 40

The snails were reared according to methods of Ebenso and Okafor (2002).

Fresh chopped green Carica papaya fruits in combination with five powdered supplementary calcium sources were fed ad libitum to the snails for 8 weeks. The weight  of each snail was recorded in the evenings on a weekly basis, using an electronic balance with accuracy of 0.01g. Mean values of weekly weight gain for each snail were calculated and subjected to analysis of variance according to a 5*4 factorial arrangement. Sources of variation were: Sources, levels, source*level interaction and error. Differences among means were assessed using Duncan’s new multiple range test (Steel and Torrie 1980) 

Calcium sources were analysed for calcium using methods of AOAC (1990). 
 

Results and Discussion

No mortality was recorded in this study, contrary to reports of Ireland (1991) that mortality occurred only in snails fed the lower calcium diets. 

Comparing other treatments with the control in the present study (Table 1), the wood-ash treatment recorded the least gain, and the  oyster shell  the highest. This agrees with the report by Daouda (1993) studying Achatina achatina fed powdered oyster shell ad libitum, separately from green forage. 

The present study agrees with Hodasi (1995) in respect of oyster shell and bone meal fed to Helix aspersa, though egg shell, limestone and wood-ash supported inferior gains. However, contrary to Hodasi (1995) the control had higher weight gain than snails given egg shell and limestone as calcium sources. There is no explanation for this. In our study, 20% Ca from the oyster shell supplement resulted in highest gains; the least weight gain was recorded for snails fed 10% Ca supplements. Ireland (1991), studying Achatina fulica, observed a reduction in the whole body weight at the highest dietary calcium concentration in which the excess calcium passed into the snail meat tissue. It could be argued that the loss of calcium into the tissue would result in weight increases, when the whole snail is weighed.  In effect, calcium metabolism in the body is in dynamic action as the element is broken down for tissue metabolism with losses through faeces thereby explaining the weight loss. 

Snail farmers often seek information on the rate of calcium inclusion in snail diets. Thompson and Cheney (1996) reported that 40% limestone flour promoted good growth in H. aspersa. Daouda (1993) used 15% oyster shell for growing A. achatina. Amubode and Ogogo (1995) used 20% bone meal and 30% oyster shell in diets for Archachatina marginata.  Our study suggests that snails will meet their calcium requirement for growth with 20% powdered oyster shell fed in combination with vegetative material.

Conclusions

• Snail meat is one of the cheapest protein sources in rural tuber and cereal based diets. Most are gathered from the wild living on soil with low exchangeable calcium.

• A short fattening period is encouraged to improve their nutritive value, which will be most beneficial to rural children and pregnant women.

• Oyster shell appears to be the best source of calcium when fed at 20% of the diet DM

References

Aboua F 1995 Proximate analysis and mineral contents of two giant African snails consumed in Ivory Coast. Tropical Science (England) 35:220-222 

Amubode F O and Ogogo AU 1995 Performance of snails (Archachatina marginata) fed varying levels of calorie-protein supplementary diets. Nigerian Journal of Forestry 24 (1 and 2): 36 – 43 

Association of Official Analytical Chemists (AOAC) 1990 Official methods of analyses.  13^th  edition, edited by Horwitz H, Washigton DC. 

Awah A A 1992 Snail farming in mature rubber plantation: 1 studies on aspects of specialized production techniques for farming Archachatina marginata. Snail Farming Research 4:33-39 

Awesu M O 1988 Observations on some aspects of reproduction of Archachatina marginata (Swainson) in captivity in a culture pen. Snail Farming Research 2:39-44 

Cobbinah J R 1994 Snail farming in West African - a practical guide. Technical Center for Agricultural and Rural Co-operation (CTA) Wageningen, The Netherlands. 

Daouda A I H H 1993 The calcium in the nutrition of giant African snail Achatina achatina. BEDIM 1 (2):25-26

Ebenso I E 2002 Consumption and sales of domesticated snails Archachatina marginata in rural southern Nigeria. Tropical Science (England) 42(4): 185-187 

Ebenso I E and Okafor N M 2002 Alternative diets for growing Archachatina marginata snails in south –eastern Nigeria. Tropical Science (England) 42(3) : 144-145 

Ebenso I E 2003a Molluscicidal effects of neem (Azadirachta indica) extracts on edible Tropical land snails. Pest Management Science (England). Accepted – in press 

Ebenso I E 2003b Nutritive potentials of white snails Archachatina marginata in Nigeria. Discovery and Innovation (Kenya). Accepted – in press 

Elmslie L J 1982 Snails and snail farming. World Animal Review (FAO) 41:20-26 

Hodasi J K M 1995 Effects of different types of food on the growth of Achatina achatina. Proceedings of the 12^th International Malacological Congress, Vigo, Spain. Edited by Guerra A, Rolan E and Rocha F. pp 488-489 

Imevbore E A and Ademosun A A 1988 The nutritive value of the African giant land snail Archachatina marginata. Journal of Animal Production Research 8(2) 76-87 

Ireland M P 1991 The effect of dietary calcium on growth, shell thickness and tissue distribution in the snail Achatina fulica. Comperative Biochemistry and Physiology 98A(1) : 111-116 

Lee M K, Moon J H and Ryu H S 1994 Nutrient composition and protein quality of giant snail product. Journal of Korean Society of Food and Nutrition 23:453-458 

Monney K A 1994 Notable notes on giant African snails. Snail Farming Research 5:1-13 

Olufokunbi B, Phillips E O, Omidiji J O, Ogbonna U O, Makonde H T and Apansile O J 1989 The economics of commercial domestication of the African giant land snail Archachatina(Calachatina) marginata (Swainson) in Nigeria. In: Slugs and Snails World Agriculture, edited by Henderson I F, Monograph no. 41, British Crop Protection Council, Thornton, Heath, pp 41-48 

Srivastava P D 1992 Problem of Land Snail Pest in Agriculture in a Study of the Giant African Snail. Concept, New Delhi, 234pp 

Steel R G D and Torrie J H 1980 Principles and procedure of statistics: a biometric approach, second edition, McGraw – Hill, New York 

Stievenart C 1992 Biology of some achatinidae known as edible snail. Proceedings of seminar on invertebrate (mini-livestock) farming, Philippines. pp 145-154  

Thompson R and Cheney S 1996 Raising Snails. Special reference and brief series 96-05 USDA/ARS/NAL, Maryland. 42pp 

Udo E J and Fayemi A A A 1975 The effect of oil pollution of soil on germination, growth and nutrient uptake of corn. Journal of Environmental Quality 4(4): 537-540.

Received 24 April 2003; Accepted 30 May 2003

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