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A Contribution to the Life History of Bucephalus longicornutus (Manter, 1954)

Number of Cercariae Liberated from Infected Oysters

Number of Cercariae Liberated from Infected Oysters

Data concerning the number of cercariae liberated from 11 infected oysters are given in Table III, which covers a 53-day period during June and July, 1964. There was a general tendency for peak liberations of more than 1,000 cercariae to be followed by lulls with few or no cercariae liberated. The duration of peaks and lulls in liberation varied considerably in the individual oysters under observation. A peak was maintained for 11 days in oyster 4 (June 10–20), while peak liberation lasted for only 24 hours in all oysters on various occasions. Peaks were generally, however, of the order of 1.5 days in duration. A lull persisted for 13 days in oyster 8 (July 3–15) but only for 24 hours in many instances. Lulls were generally more variable in duration than peaks.

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Table III.—Numbers of Gercariae Liberated from 11 Infected Oysters over a 53-day period During June and July, 1964.

Table III.—Numbers of Gercariae Liberated from 11 Infected Oysters over a 53-day period During June and July, 1964.

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The maximum number of cercariae liberated from one oyster over a 24-hour period was 10,000, and this occurred on one occasion in oysters 2 and 11, and on two occasions in oysters 4 and 10.

Towards the end of the observation period there was a marked tendency for peaks in liberation to become less frequent. This might suggest that the infection was abating but this has been discounted elsewhere (Howell, 1966, in press). More probably, only one change of water per day for each oyster is insufficient to provide the necessary food requirements to maintain both oyster and parasite and this is reflected in fewer cercariae produced and liberated. It is difficult to adjudge from the results obtained any effect of temperature (which fluctuated between 10–15°C) on the production and liberation of cercariae. However, despite these points, the net results suggest that liberation of cercariae is neither cyclic nor continuous but essentially an intermittent phenomenon.

It should be noted that it was possible to determine the state of the infection in individual oysters when they were opened after completing the above observations. As expected, the number of cercariae liberated from a given oyster could be correlated with the state of the infection. Oysters 3, 6, 7, 8 and 9 proved to be relatively lightly infected; oysters 1 and 11 moderately heavily infected; and oysters 2, 4, 5 and 10 heavily infected.