Measurements of Feeding, Food Assimilability, and Respiration
143
and with addition of portions of hydrolyzed tissues of the same unlabeled
animals in quantities approximately equal to those in the radioassays for the
Re estimations. The latter is necessary to equalize the counting efficiency to
avoid the quench correction.
Many aquatic animals (cladocerans, for example) do not form rigid feces.
They rapidly dissipate in water. In this case, in a part of the filtrate remaining
after the separation of rigid feces, the radioactivity of dissolved and colloidal
organic matter which has passed through the membrane filters must also be
measured. It can be done in the same way as described above for the exudated
phytoplankton primary production (see Sect. 2.3.1.7). When all the above
listed radioactivity values are assayed under quasiequal counting conditions
and calculated as cpm sp.-l, all necessary parameters for assessment the assimilability index I can be calculated as related to the time of feeding of animals
with the labeled food: I = (Ra + Re) (lOOlRe %. Correspondingly, the values of
the members of the balance ratio for the same time period are calculated as
follows: the food ration (Q): Q = ReC" or Q = (Ra + re + Rf)Cr Ilg CSp.-l. The
assimilated food (A): A = (Ra + re) Cr IlgCSp.-l; the nonassimilated food (F):
F = R f Cr, IlgCSp.-l; the expenditures for growth (G): A - M IlgCSp.-l (if M is
the respiration rate calculated in Ilg CSp.-l per same time interval as A) and
the secondary production efficiency coefficients (KI and K l ): KI = G/Q, and
Kl = G/A.
3.6.3 Estimations of Aquatic Animal Nutrition
with Dissolved Organic Matter
3.6.3.1 General Remarks
The problem of so-called osmotic nutrition of aquatic animals with dissolved
organic matter deserves special attention as it constitutes an important field
for the use of radiocarbon technique in aquatic trophology. An old speculation by Putter (1907) about the importance of organic matter dissolved in
water as probable food source for aquatic animals acquired a second life in
the late 1960-early 1970s, when it was discovered that many marine animals
readily consume radiolabeled glucose and amino acids, even at micromolar
concentration in water (Stephens 1964, 1968; Khailov 1971a,b; Southward and
Southward 1972; Sorokin 1973a; Sorokin and Wyshkwartzev 1973). At that
time, this line of study underwent a veritable boom. Many authors measured
uptake of dissolved organic compounds labeled with 14C without heeding the
presence or possible appearance of bacteria in water during their experiments.
Most of them did not even measure the specific radioactivity of carbon in the
labeled compounds thus used, which often happened to be very high, up to
10 6 _10 7 cpm per severalllgC (Reish and Stephens 1969). In this case, a very
high radioactivity discovered in the animals' bodies could correspond to a negligible absolute uptake, if the specific radioactivity was indeed so high. This
143
and with addition of portions of hydrolyzed tissues of the same unlabeled
animals in quantities approximately equal to those in the radioassays for the
Re estimations. The latter is necessary to equalize the counting efficiency to
avoid the quench correction.
Many aquatic animals (cladocerans, for example) do not form rigid feces.
They rapidly dissipate in water. In this case, in a part of the filtrate remaining
after the separation of rigid feces, the radioactivity of dissolved and colloidal
organic matter which has passed through the membrane filters must also be
measured. It can be done in the same way as described above for the exudated
phytoplankton primary production (see Sect. 2.3.1.7). When all the above
listed radioactivity values are assayed under quasiequal counting conditions
and calculated as cpm sp.-l, all necessary parameters for assessment the assimilability index I can be calculated as related to the time of feeding of animals
with the labeled food: I = (Ra + Re) (lOOlRe %. Correspondingly, the values of
the members of the balance ratio for the same time period are calculated as
follows: the food ration (Q): Q = ReC" or Q = (Ra + re + Rf)Cr Ilg CSp.-l. The
assimilated food (A): A = (Ra + re) Cr IlgCSp.-l; the nonassimilated food (F):
F = R f Cr, IlgCSp.-l; the expenditures for growth (G): A - M IlgCSp.-l (if M is
the respiration rate calculated in Ilg CSp.-l per same time interval as A) and
the secondary production efficiency coefficients (KI and K l ): KI = G/Q, and
Kl = G/A.
3.6.3 Estimations of Aquatic Animal Nutrition
with Dissolved Organic Matter
3.6.3.1 General Remarks
The problem of so-called osmotic nutrition of aquatic animals with dissolved
organic matter deserves special attention as it constitutes an important field
for the use of radiocarbon technique in aquatic trophology. An old speculation by Putter (1907) about the importance of organic matter dissolved in
water as probable food source for aquatic animals acquired a second life in
the late 1960-early 1970s, when it was discovered that many marine animals
readily consume radiolabeled glucose and amino acids, even at micromolar
concentration in water (Stephens 1964, 1968; Khailov 1971a,b; Southward and
Southward 1972; Sorokin 1973a; Sorokin and Wyshkwartzev 1973). At that
time, this line of study underwent a veritable boom. Many authors measured
uptake of dissolved organic compounds labeled with 14C without heeding the
presence or possible appearance of bacteria in water during their experiments.
Most of them did not even measure the specific radioactivity of carbon in the
labeled compounds thus used, which often happened to be very high, up to
10 6 _10 7 cpm per severalllgC (Reish and Stephens 1969). In this case, a very
high radioactivity discovered in the animals' bodies could correspond to a negligible absolute uptake, if the specific radioactivity was indeed so high. This