A series of experiments were carried out with a view to obtain some knowledge of the influences of temperature, salinity and pH upon the oxygen consumption of young
Pagrosomus major (T. & S.), as well as upon the oxygen content in the medium
pm. at the time when the fish ceases to breathe.
In every single experiment one or two fishes were put in a glass vessel containing 3, 000 c.c of sea water, on the top of which a layer of 4cm. of paraffin oil was placed in order to avoid the direct contact of air. Samples of 300 c.c. each of the water were collected at times after suitable intervals, to estimate the oxygen content and pH, for the former of which W
INKLER'S method was employed while the latter was determined colorimetrically.
As the volume
V of sea water in the vessel is reduced by
v (=300 c.c.) in each sampling,
V after the
n-th sampling is
V0-
nv, where
V0 is 3, 000 c.c. Denoting by
pn,
θn and (
Hp)
n the oxygen content, temperature and pH of the
n-th sample respectively, the total amount of oxygen consumption during the time interval,
t hours, between the (
n-1)-th and
n-th samplings is (
pn-1-
pn) (
V0-
-n-1
v)
2. We may take (
pn-1-
pn)(
V0-
-n-l
v)/
t,
θn-1+
θn/2, (
pH)
n-1+(
pH)
n/2, and
pn-1+
pn/2 as oxygen consumption per hour, temperature, hydrogen-ion concentration and oxygen content during the interval above said respectively.
On combining and analysing the results ofcalculations, we first assumed that the difference in pH or in density of the medium reduced to temperature 15°C,
ρ, does not more influence the oxygen consumption nor
pm than other factors do, provided the value of pH or of (
ρ-1)×10
3 lies in an assigned range, and then, after proceeding the analysis on the influences of the other factors, -under the reasoning about the other cases by analogy-, the observed values of oxygen consumption or
pm were reduced to those in a standard condition where the other factors are constant. Finally the assumption was justified, using those reduced values. In such a manner, the following conclusions were drawn.
(1) The oxygen consumption per hour is proportional to the total weight of fish put in the vessel, providedtemperature and oxygen content, besides pH and (
ρ-1)×10
3 are constant. (Fig. J.)
(2) The oxygen consumption per hour per unit weight of fish isproportional to the oxygen content, provided temperature, besides pH and
ρ, is constant (Fig. 2).
(3) The relation of the oxygen consumption per hour per unit weight of fish per unit amount of oxygen content, q, to temperature follows A
REHENIUS'S law (Fig. 3), and we obtain
Q10=2.6.
(4) The influence on q of difference in salinity is but slight, judging from the values of the former reduced to a certain temperature, say 21°C., except when
ρ is as low as 1.005 (Fig. 5).
(5) The relation between q, reduced to 21°C., and pH (Fig. 4) suggests that there exsists a maximum of the former at pH=ca. 8.0, though the data for pH>8.3 are lacking, agreeing J. R. J. R P
EREIRA'S observations with
Fundulus helerochtus.
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