Effects of Different Kinds of Food, Starvation and Restart of Feeding On the Haemolymph-Glucose of the Pond Snail Lymnaea Stagnalis

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Abstract
In the present study, the amount of glucose and of some other carbohydrate com- ponents in the haemolymph of laboratory bred specimens of Lymnaea stagnalis was studied in relation to different feeding conditions. The snails, normally fed on lettuce, were fed on a carbohydrate rich diet (Bemax), were starved, or were fed again after a period of starvation. It is demonstrated that the haemolymph-glucose concentration has a rather constant level of 16μg/ml in lettuce fed snails. This level, however, can be slightly different for snails originating from various breeding tanks. During starvation (up to 15 days) the haemolymph-glucose remains at the same constant level as in lettuce fed snails. Reproduction and growth stop and especially the former will cause a reduced need for glucose. Some glucose, however, is needed for metabolism. It is suggested that the haemolymph-glucose is maintained at a constant level during adverse conditions (such as starvation) at the expense of, mainly, polysaccharides present in the vesicular connective tissue cells and in the reproductive organs. When feeding again on lettuce after a period of starvation and when feeding on a carbohydrate rich diet (Bemax), within 1 day the haemolymph-glucose level is raised (to 36 μg/ml and 144 μg/ml, respectively) above the level of lettuce fed control snails. This raise in the glucose concentration in the haemolymph is only temporary in the animals fed again on lettuce. After 7 days of feeding the glucose level is no longer significantly different from the value of lettuce fed control snails. Also reproduction and growth are resumed after this period. It is suggested that a raise in the glucose concentration in the haemolymph (caused by the restart of feeding) is a stimulus for the start of reproduction and growth. The raise in the glucose concentration in the haemolymph of snails fed on Bemax, lasts during the whole experimental period (7 days). At the end of this period the haemolymph has a raised, constant glucose concentration of 86 μg/ml which re- presents an equilibrium between the increased glucose influx in the haemolymph and an increased use of glucose by glucose consuming processes like storage and reproduction.

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