Growth, Age Determination and Longevity in the Giant African Snail Archachatina marginata (Swainson)

Abstract

Growth rates in terms of shell lengths were investigated in four subspecies of Archachatina marginata (Swainson) under culture conditions. Number of shell whorls, shell pigmentation and microsculpture were also studied to assess their usefulness in age determination. The snails displayed a sigmoid growth pattern, with growth slowing down after 8 months of life. In the first 8 months, the mean daily growth rates in the four subspecies showed a range of 0.21-0.25 mm/day, while between 8 - 12 months the range was 0.11-0.13 mm/day. Between 12-15 months the growth rate had considerably fallen to 0.02-0.06 mm/day. The observed differences in growth rates between the subspecies were however not significantly different (p>0.05) in the first 12 months of growth. In terms of maximum sizes attained after 21/2 years of growth, A. marginata eduardi reached a shell length of 88.7 mm which was distinctly smaller (P<0.05) than the values for the other subspecies. A marginata marginata attained the largest shell length of 142.6 mm while A. marginata suturalis and A. marginata grevillei attained shell lengths of 121.4 mm and 102.5 mm, respectively. This study further showed that shell colouration as well as microsculptural patterns on the body whorl were of little or no use in age determination. However, snails could be classified into four age brackets, using the number of visible whorls on the shell. The longevity test showed that the oldest snail in the farm lived for 61/2 years. The implication of this studies for snail culture is that, in semi-intensive systems with minimal input, giant snails can be kept up to 11/2 years for them to reach competitive market sizes.


Key Words: Archachatina marginata, age determination, growth, longevity.


Int. J. Agric. Rural Dev., 2003, 4: 46-52