620 
BULLETIN OF THE BUREAU OF FISHERIES 
From the foregoing evidence it is difficult to determine the lowest salinity which 
the bay scallop will temporarily survive. A salinity as low as 6 parts per mille evi- 
dently is destructive. In various instances salinity reductions to 13-14 parts per 
mille have not proved quickly fatal to adults and there is evidence of ample survival 
by young during a period of salinity reduction which on two succeeding days was as 
low as 14 parts per mille. (See table 8 and fig. 31). In contrast we find in 1928 
scallops at Pivers Island dying in appreciable numbers and apparently because of 
a freshet which was not found to go below 18.6 parts per mille. In the case of adults, 
at least, the delay between undue freshening (unless it is extreme, as in 1924) and 
death seems to be extraordinary (weeks or even months). Death from freshets may 
occur considerably after an improvement in salinity. 
» One of the possibilities suggested by the inconsistent results of water freshening 
is that not NaCl reduction but some change in minor constituents is the major factor 
in the destructiveness of freshets. 
With a more hardy form, definite experimental information as to permissible 
salinities would have been sought. The great uncertainity of scallop survival in 
aquaria was taken to indicate as unwise efforts in this direction. 
Although a distributional as distinguished from a temporary minimum salinity 
is here considered, it is possible that the prevailing or so-called distributional mini- 
mum is merely incidental, and that the only functional minimum — where considerable 
fluctuations occur — is the temporary, and that it depends on the length of time 
involved and even on the prevailing salinity. 
The evidence was at first taken to point to a correlation between growth and 
salinity. Later investigations, however, pointed to current as the principal factor, 
and no clear relationship between salinity and growth was found. 
A temporary reduction in salinity “fattens” or “swells” scallops by lowering 
the osmotic pressure of the surrounding medium so that the tissues of the scallop 
absorb water and become distended. Thus in Core Sound, where the tidal effect of 
wind is pronounced, a cold snap with its northerly wind and consequent influx of less 
salty water from Pamlico Sound, results in plump scallops and has led to the belief 
that sudden cold fattens scallops. 
TEMPERATURE 
Upon the feeding and growth of various lamellibranchs, water temperature has 
been found to exert a profound direct effect. At a temperature approaching 0° C., 
the activity of gill cilia nearly ceases so that syphoning (and consequently feeding) 
becomes negligible. Up to a limiting temperature (in certain instances in the neigh- 
borhood of 30° C.) the ciliary activity and rate of syphoning increases with the tern 
perature. Thus Round (1914), studying the rate of bacterial elimination in oysters, 
found that above 9° C. there was evidence of pronounced gill currents, but that at 
5° C. only after five days was there reduction; Nelson (1921) found that from 0° to 
5° C. the feeding current of the oyster was extremely minute; Gray (1923) states 
that the ciliary speed ( Mytilus edulis ) increases from 0° to 33° C.; and Galtsoff 
(1926) found that the optimum (for the oyster) lies between 25° and 30° C. with 
no current produced at or below 5° C. 
Examination of the temperature graph (fig. 32) and Table 10 shows that water 
temperature at Pivers Island varies from a minimum of 3° to 6° C. generally in Jan- 
uary, to a maximum of 30° to 33° C. in July, August, or September. This, and the 
generally even character of the maximum and minimum curves, would suggest a 
cycle of growth beginning with zero or nearly that (and a growth line) in January 
