522 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [6] 
ponds; the tamarind is the only tree capable of resisting the force of 
the wind on the shores of the basin of Arcachon. 
(3.) Pits are dug in the shape of holes or trenches, thus creating de- 
pressions in the ground, 1.30 to 2 meters (and more) deep, where the 
mullet can take refuge either during great heat or severe frost. These 
pits are particularly beneficial to the fish when they cause fresh water 
to flow into the ponds. The temperature of this subterranean water, 
which is nearly always thesame, 8 to 12 degrees, hasavery salutary effect, 
by cooling off the water of the fish-ponds in summer, by keeping up a 
suitable degree of saltness, and by preventing the sheets of water from 
freezing in winter. When the surface is frozen, care should be taken to 
break the ice at regular intervals, so as to establish the proper circula- 
tion of air. For this purpose holes are made in the ice, and fagots or 
bundles of sticks whose ends are mixed with straw, either in small 
quantity or in sheaves, are stuck in the holes. Without these precanu- 
tions one would run the risk of losing a large number of mullet, which 
often gather in the pits in dense masses, and there die from asphyxia. 
(4.) Fresh water is brought into the ponds from neighboring water- 
courses, or from ponds or wells dug in the neighborhood. Such water, 
by reason of its composition and temperature, produces the same result 
as subterranean water obtained by digging. 
Raising and fatltening.—The deep places of a pond are specially in- 
tended to afford shelter to the fish, but they would not answer the 
purpose of raising fish, the rapid development of the fry and the fatten- 
ing of the grown fish, especially the herbivorous kinds, like the mullet. 
With the view of supplying the necessary conditions for raising fish, 
pastures are provided for them—shallow portions of the pond where 
those plants will grow which serve as food for the fish. These pasture- 
lands generally occupy vast plains on the bottom of the pond, where 
the fish can rest and feed, and where they are exposed to the direct 
influences of air, light, and sun. The best pasture-lands are those por- 
tions of the pond which present an extensive plain, very deep, and with 
scanty vegetation. 
On these pasture-lands the fish might be surprised by cold winds, 
and might perish in large numbers. In order to protect them, and pre- 
vent them from straying away, the water of the fish pond is lowered 
from the lst November to about the 15th March. This causes the fish 
to seek the deep and sheltered places, where they are protected from 
hurtful winds, and where they can easily be caught, whenever there is 
any demand for fish. 
The vegetation of the pasture-land and that of the pond in general is 
of great importance for raising fish. 
Aquatic plants not only afford shelter to the fish, but also supply 
them with food, both in a fresh condition and when decayed. These 
plants also contribute indirectly to the food of fish by serving as shel- 
ter and nourishment to a very large number of small aquatic animals, 
