DIATOMS AND LOBSTER REARING 17 
SESSIONAL PAPER No. 38a 
healthy and active for several days. If, as stated, diatoms require for their destruc- 
tion one part of copper sulphate per million, it is clear that this algicide cannot be 
used in sea-water in the presence of lobster larve. 
Fig. 5. 
Drawing of lobster larva, twelve days old, exposed 
to sunlight every day. These larvae were all 
dead by the fourteenth day. The appendages 
are loaded with diatoms. 
The second plan of control gave more promising results. For a plant to make 
its own food, sunlight is necessary. Diatoms, being independent plants, must have 
sunlight in order to make satisfactory growth. Ten thousand larve in one rearing- 
box were exposed to the light as usual, while a like number in a neighbouring box 
were kept shaded by a screen of canvas painted black, and placed horizontally over 
the box, within about 6 inches of the surface of the water. The larve were already 
four days old when the shade was applied, and on an average they carried between 
350 and 500 diatoms each. They were examined after forty-eight hours of shading, 
and an improvement in their condition was apparent. Careful counts gave an average 
of 209 diatoms on each larva. Daily examination showed a satisfactory decrease in 
the number of diatoms. These shaded larve began moulting at the end of nine days, 
while those unshaded did not moult until they were thirteen days old. At the end of 
twelve days the shaded larvee were active, and apparently suffering no inconvenience 
from the few diatoms that adhered to them. This was in striking contrast to the 
larvee which had not been shaded, and which were loaded with masses of diatoms on 
every appendage, as indicated in the drawings. 
