DIATOMS AND LOBSTER REARING 13 
SESSIONAL PAPER No. 38a 
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3. ImporTANCE oF DiAtoms to FIsH. 
The complete dependence of animal life on plant life is recognized by all. 
Diatoms are probably the most important of those very simple plants which take up 
inorganic substances from water and air, and transform these by the aid of sunlight 
into living organic matter. 
This organic matter then serves as the chief food of crustaceans and mollusks 
on which many fish live. The most careful study of aquatic life gives to diatoms 
the proud position of being’a large part of the fundamental food on which the animal 
life of the water depends, and in this sense the expression is true that “ All fish are 
diatoms.” 
4, STRUCTURE OF DIATOMS. 
Diatoms are plants of the simplest kind, that is, each diatom consists of but 
one cell, and a cell is the simplest thing that can be recognized as alive. The greatest 
peculiarity of diatoms is the fact that each one has a skeleton of silica which 
is mostly outside the plant, and therefore might be called a shell or case. This shell 
is often very beautifully marked with lines of nodules or of depressions or of both, 
and these markings are so minute that they were long thought to be merely grooves 
and ridges. Diatoms may well be compared with bacteria, which are also minute 
plants. Diatoms differ from bacteria in being usually very much larger, in having 
the siliceous shell, and in having chlorophyll. This latter substance enables them 
to use the sunlight in making their own food, while bacteria, lacking chlorophyll, 
have to absorb food made by other plants. Bacteria are therefore classed with that 
large group of dependent plants—the fungi, while diatoms rank with the independent 
plants. Diatoms reproduce in much the same way as do bacteria, that is, by each 
mature diatom splitting into two diatoms, after the two valves of the shell have been 
pushed apart by the growing protoplasm within. Two new valves or half-shells are 
then formed, and thus each new diatom has one old valve and one new one in its 
shell. This splitting process, as in bacteria, may go on very rapidly if food and 
temperature be favourable, and it will result, at any point, in doubling the numbers 
of diatoms many times in a few days. 
In form, diatoms are exceedingly various, such as discoidal, cylindrical, spindle- 
shaped, and wedge-shaped. Some are made up of segments, which are smooth or 
spiny, and variously fastened together; some form long ribbons by adhering closely 
side by side; others occurs in gelatinous tubes in which the individuals are closely 
packed. The majority of them are free and have some power of locomotion, but 
some grow attached to larger objects by gelatinous adhesions or even stalks. Of 
this latter sort are the kinds which have proven so prejudicial to the growth of the 
young lobsters. 
