28 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
second year, unlike those at Kaida. Therefore, at Ivusatsu, to the end of growing 
a larger oyster, the culturist divides his parks into three classes: those of shallow 
water (largely for spat collecting), early rearing, and deep water (for late rearing). 
The cultural concessions accordingly have come 
to he arranged with their long axes at right 
angles to the shore, thus providing a range of 
water passing from shallow water to deep, each 
lot measuring, in round numbers, a thousand 
feet by fifty. In shallower waters, tempered by 
fresh streams from the direction of Hiroshima, 
are the best conditions for spat-collecting. 
Here the specific gravity is very nearly the same 
as in Kaida Bay — in summer about 1.018; in 
winter 1.020. The density of the water rises 
gradually and attains about 1.025 in the deepest 
zone. Accordingly, the shallowest region in 
each park usually becomes laid out in a zone of 
collectors, or shibi-ba, and resembles somewhat 
Kaida Bay. In the next and deeper ground 
are the rearranged and oyster-bearing shibi (of 
the shallower zone), toya-ba, and in the deepest 
water are the typical oyster beds, or miire-ba. 
Of course such an arrangement is sometimes 
modified, since practice demonstrates that the 
local conditions of an oyster park, e. g., water 
currents, are apt to warrant widely different 
treatment. 
(a) In the shallow zone an arrangement of shibi in lines parallel to the shore 
is the common one. Between the rows are intervals of about 4 feet, the park in 
this case resembling one of the common type of Kusatsu (fig. 8). Often, however, 
the shibi are shorn of their branches and 
planted like canes (3 to 5 feet in length) 
in close-set rows. Such, for example, are 
the shibi photographed in plate 6, A, B, 
and C. The first of these, A, has had the 
oysters attached to it for about a month; 
the second, B, for about 6 months, and the 
third, C, for about 18 months. It is at 
the last period that the masses of oysters 
come to separate somewhat readily from 
the bamboo. In these parks the arrange- 
ment and treatment of the shibi varies 
greatly in accordance with local condi- 
tions. In rapid currents, which distinguish 
the region of Kusatsu, short and branchless shibi are commonest, these, too, made 
of the strong and short-jointed species of bamboo, “madake.” Their arrangement 
is frequently in clumps, or toya, as indicated in figs. 20 to 23. Of these the toya 
Pig. 17. — Mitten of heavy sack cloth, open at 
thumb and finger tip, used to hold the oyster- 
bearing shibi while separating the oysters. 
Pig. 18 .- 
-Basket, taruyama kayo, for collecting and 
storing marketable oysters. 
