﻿SNAIL HOST OF ORIENTAL LUNG FLUKE — ABBOTT 99 



The water-temperature limits of this species were not appreciated 

 until a survey was made of the Lithia Spring, Fla., populations. In 

 aquaria and the spring, where the temperature remains around 76° F., 

 the snails are able to maintain themselves in adequate numbers. How- 

 ever, just beyond the influence of the warm waters of the spring, where 

 the cooler waters of the local river are about 50° F. or less, the snails 

 are absent. The overflow ditch outside the extensive plant aquaria 

 in Tampa is colonized by these snails during the warm summer months, 

 but in winter, when the water temperature is as low as 50° F., these 

 snails die off. The temperature recordings for Guam streams and 

 even for the rivers at 3,000 feet altitude on Leyte Island were all 

 above 75° F. 



BIONOMICS 



Growth and size. — The rate of growth of the shell has not been de- 

 termined, although, from common experience in raising these snails 

 in aquaria, it is assumed that adult size or maturity is reached within 

 6 to 12 months. Two preliminary studies were made of the character 

 of shell size, one on the 13 colonies collected on Guam Island, the other 

 on the populations of Lithia Spring. In the latter study, dissections 

 were made to determine the size at which individuals become sexually 

 mature, for there is no tell-tale flaring or thickening to the outer lip 

 that often accompanies maturity in many other molluscan species. 



The significant differences in the size of samples taken at various 

 places in the spring, only a few dozen yards from each other, are 

 extremely important in demonstrating the wide range in size exhibited 

 by one species. The aquarial stock from which these snails originated 

 grew to a size almost four times that of its offspring in the spring. 

 Only in an isolated, subsidiary spring, a few yards from the main 

 spring, did specimens reach a size comparable to the aquarial stock. 

 In all likelihood the differences in size exhibited by the seven sample 

 populations in the spring have been brought about by ecological and 

 not genetic factors. Not only are the means of shell lengths and maxi- 

 mum sizes of shell considerably varied, but the points at which ma- 

 turity is reached are correspondingly shifted. This latter fact ex- 

 cludes the premise that these colonies represent aggregates of smaller, 

 younger individuals. No direct correlation between diminutive size 

 and type of bottom, depth of water, temperature of water, amount of 

 shade, or distance from source of spring could be found. The small 

 colony in the adjacent subsidiary spring attained a shell size nearly 

 three times that of colonies in the main spring. Relatively few speci- 

 mens per square foot were found in the smaller spring, while in the 

 main spring overcrowding was evident, sometimes reaching a popula- 

 tion density of 400 specimens per square foot. It is likely that food 

 availability is the most important factor, but controlled experiments 

 alone will support this assumption. 



