Biochemical evaluation of aestivation and starvation in two snail species

Abstract

There is resurgence in incidence of schistosomiasis in Nigeria with attendant socio-economic and health impact. The agents transmitting this disease are the Bulinus snails which employ aestivation to survive conditions of unfavourable weather such as lack of food and water. The mechanism of aestivation under aridity and drought is not clear. This study therefore investigated the effects of aestivation and starvation on endogenous metabolic reserves in haemolymph of two snail species namely: Bulinus globosus (Morelet) and Bulinus rohlfsi (Clessin). Aestivation, starvation and control experiments were set up for 30  days in the laboratory by placing three groups of snails collected from Oyan dam, Abeokuta in  standard aestivation slope (30 B. globosus and 19 B. rohlfsi), aquarium (30 B. globosus and 23 B. rohlfsi) and control slope which had 20 B. globosus and 15 B. rohlfsi. Aestivation and control slopes contained water and mixture of sand and clay (3:1), while aquarium contained water only for starvation. All the snails were fed on lettuce ad libitum for 28 days during which water was completely drained out in the aestivation slope. The aestivation slope and aquarium were left for another 30 days without lettuce.  Snails were thereafter sacrificed and haemolymph biochemical parameters were assayed. In aestivating and starving B. globosus, haemolymph creatinine, urea, total protein, glucose, alanine transferases (ALT) and aspartate transferases (AST) were significantly decreased, while haemolymph total  cholesterol, triglyceride and a-amylase concentrations and activity increased significantly (p < 0.05). In B. rohlfsi, creatinine, urea, ALT and AST were significantly decreased when compared with controls (p < 0.05). B. globosus and B. rohlfsi possess ability to survive unfavourable conditions by economical utilization of stored metabolites, thus enabling them to carry infection from one season to the next. Our findings suggest that B. globosus is a better aestivator than B. rohlfsi.

Key words: Aestivation, enzymes, Bulinus globosus, Bulinus rohlfsi, schistosomiasis.