SH 370 
 .M5 
 
 Copy 1 
 
 Vv^- 
 
 I 
 
yjy. 
 
 FROM BULLETIN OF THE UNITED STATES BUREAU OF FISHERIES : VOLUME XXXII. 1912 
 Document 787 ::::::::::::: Issued February 18, 1914. 
 
 THE OXYGEN REQUIREMENTS OF SHELLFISH 
 
 By Philip H. Mitchell 
 
 16284" — J4 
 
 207 
 

 d; of d. 
 
 fif*Aii 4 5914 
 
THE OXYGEN REQUIREMENTS OF SHELLFISH. 
 
 By PHILIP H. MITCHELL. 
 
 The respiratory exchanges in lamelUbranchs seem not to have been investigated. 
 Probably the most notable work related to it is that of Vernon." He measured the oxy- 
 gen utilization and carbon dioxide emission in a large number of marine forms, including 
 certain MoUusca but no lamellibranchs. He showed that in the lower marine forms 
 investigated, including Coelenterata, Tunicata, and Mollusca, the respiratory exchange 
 was very small compared to the higher ones, for example, teleosts. There were, however, 
 certain exceptions to this rule, notably the protozoan Collozoum inerme, which showed 
 nearly as high a respiratory exchange as the fishes. He found also that, in general, the 
 respiratory activity was more readily responsive to temperature in the lower than in 
 the higher forms. He further showed that the gaseous exchange was relatively greater 
 in the small than in the large individuals of the same species and found that, in general, 
 the same distinction held between small and large species. The transparent pelagic 
 animals were shown to have a very small proportion of soUd organic matter in their 
 tissues, so that calculated on that basis their respiratory activity was very large, greater 
 indeed than fishes, amphibians, or even mammals. 
 
 In the present work some of those findings have been confirmed for the lamelli- 
 branchs. They show a ready responsiveness to temperature changes, a smaller utili- 
 zation of oxygen in proportion to the body weight with increase in size, and those forms 
 which showed a low oxygen requirement in relation to their entire weight showed a 
 higher utilization in proportion to their dried weight. 
 
 The resistance to lack of oxygen in forms which have no power of locomotion is 
 an important factor in adverse conditions. This is especially true of the edible shellfish, 
 which, because of enforced closure during cold weather, or in the presence of polluted 
 or roily water, or in water whose oxygen has been lowered by the presence of certain 
 wastes or an abundance of life, must at times be deprived of their normal supply of 
 oxygen. The subject therefore possesses an economic significance, and it was, in fact, 
 the possibility that certain manufacturing wastes, removing oxygen from sea water, 
 might therefore cause the death of oysters and clams which first directed the writer's 
 attention to the subject. The particular wastes involved were those of gas works con- 
 
 f Vernon. H. M.; Respiration in marine forms. Journal of Physiology, vol. XIX, 1895, p. 18. 
 
 209 
 
2IO BULLETIN OF THE BUREAU OF FISHERIES. 
 
 taining at least traces and sometimes significant quantities of water-gas tar and other 
 oily matter. The results of this investigation indicate, in a word, that the tar or oily 
 wastes could have no effect on shellfish in this way. The details of this part of the work, 
 however, are reserved for a report dealing specifically with the effect of water-gas tar on 
 oysters. This paper is confined to oxygen requirements of shellfish and their resistance 
 to lack of oxygen. 
 
 METHOD OF EXPERIMENT. 
 
 The method of manipulation was, in brief, to place the shellfish in a desiccator 
 completely filled with sea water of known content of dissolved oxygen, leave the apparatus 
 at some constant temperature during a definite period, and then to sample the water 
 in the desiccator so as to compute its decrease in dissolved oxygen. Winkler's well- 
 known titration method was used to measure the oxygen both at the beginning and end 
 of each experiment. A vacuum desiccator was used for the containing vessel because 
 it could easily be closed water-tight, could accommodate almost any size of shellfish, 
 and enabled one to take through the side opening with glass stopcock a fair sample of 
 the contents. 
 
 In practice a number of precautions were found necessary. The hollow dome of 
 the desiccator cover was entirely filled with paraffin to exclude air from entrapment 
 in it. A glass tube within the desiccator was connected to its side stopcock and reached 
 nearly to the bottom. When, therefore, the filled desiccator was opened at the top 
 water could be sucked off through the opened side cock into the sampling bottle so that 
 the sample would come from a point well below the surface of the water, where the oxy- 
 gen content would be fairly constant. The sea water " used in each experiment was 
 brought to the required temperature and placed in a large reservoir jar on a shelf, from 
 which it could be siphoned without bubbling into the desiccator. When it was thus 
 nearly filled, an oyster was gently placed on a glass tripod, where it would rest near the 
 center of the desiccator. With clams it was found necessary to leave them in the 
 desiccator submerged in water for a few hours before the experiment, because, unlike 
 oysters, they would not open quickly after they had been handled. In either case, 
 though, water from the shelf reservoir was siphoned into the overflowing desiccator for 
 sufficient time to bring the oxygen content to approximate constancy and then the 
 cover was put on, leaving just opening enough to admit the siphon tube. 
 
 The side cock of the desiccator was then connected by rubber tubing to the sampling 
 bottle, and after starting by suction the water was allowed to siphon through the bottle 
 two to three minutes. This period was found quite sufficient to give reliable duplicate 
 results for water containing any percentage of oxygen measured in these experiments. 
 The water running into the desiccator meantime was in excess of that running into the 
 bottle, so that an overflow was maintained from the top of the desiccator and the sample 
 rendered as fair as possible. At the exact second recorded as the beginning of the experi- 
 ment the side stopcock was closed, the siphon quickly withdrawn from the desiccator, 
 
 " From aquarium of running sea water, a part of the aquarium system of the laboratory. 
 
OXYGEN REQUIREMENTS OF SHELLFISH. 211 
 
 and its lid put completely on, excluding bubbles. The entire apparatus was then kept 
 in a bath of sea water whose temperature was maintained approximately the same as the 
 water within the desiccator. The oxygen in the sample was meantime measured by 
 titration. 
 
 After a period, usually about an hour in lengthy the desiccator was two or three times 
 inverted to render its contents uniform and to stimulate the shellfish to close and thus 
 stop using oxygen. The exact time of the first rough movement of the apparatus was 
 recorded as the closing time of the experiment. The outside of the desiccator was then 
 dried with a towel and the entire apparatus weighed. When currents in the water had 
 come practically to rest, the side stopcock was again connected to the same sampling 
 bottle used at the beginning of the experiment and a sample taken as before. Since 
 the capacity of the desiccators was sufficient for 1,200 grams of water, even with the 
 large shellfish, and as the sampling bottles held approximately 300 grams, it is plain 
 that water could run through the sampling bottle some time without emptying the 
 desiccator. The stream indeed was allowed to run at least two minutes. The capacity 
 of the desiccators was not enough to permit of taking a duplicate sample that would be 
 reliable, but this was not necessary because there is little chance of error in the Winkler's 
 titration. 
 
 The last step in the process was to empty the desiccator completely, dry it and the 
 shellfish, and weigh them together. This gave a means of determining by difference the 
 weight of the water. It was probably accurate to within 2 grams. As the dissolved 
 oxygen of the water both at the beginning and the end of the experiment was calculated 
 in parts per million, it was only necessary to multiply the weight of water used by the 
 decrease in its oxygen content expressed in parts per million and divide the result by 
 100 to find the decimilhgrams of oxygen used by the shellfish. Experiment showed that 
 no correction for change in the oxygen content of the water due to microorganisms or 
 physical factors was, under the circumstances of constant temperature, etc., necessary. 
 Results were expressed in decimilligrams of oxygen per hour and in most cases also com- 
 puted in decimilligrams per hour per 100 grams of shellfish and in some cases in decimil- 
 ligrams per hour per i gram of the dried weight of the total shell contents of the organism. 
 
 A formula for the first of these three computations might be expressed, therefore, as 
 
 follows : 
 
 ,a'-a" 60 
 
 A=W- 
 
 100 / 
 
 where A is the decimilligrams of O used per hour, W the weight, in grams, of water in the 
 desiccator, a' the parts per million of oxygen in the first sample and a" in the second 
 sample, and t is the time of the experiment in minutes. 
 
 Throughout the experiments it was found necessary to observe the animal at fre- 
 quent intervals, and if the shells closed up to discard the experiment, or if the shells 
 closed only after a considerable number of minutes had elapsed to terminate the experi- 
 ment immediately. This precaution was necessary because, as is well known, certain 
 of the shellfish used in this work can close water tight and in that condition take from the 
 
212 BULLETIN OF THE BUREAU OF FISHERIES. 
 
 water, as will be shown below, no oxygen except the very small amount absorbed by 
 their shells. 
 
 It appeared early in the work that constancy of results was exceedingly difficult to 
 obtain. This was due to a variety of causes, chief of which was the great variability in 
 the openness of the shells, for not only could the oyster or clam entirely or at least 
 obviously close so that the experiment had to be terminated, but it could partially and 
 unnoticeably close or indeed fail to open wide even from the beginning of the experiment. 
 For the oyster, at least, the author succeeded in demonstrating this by graphic records. 
 One shell of an oyster was connected by tying a string to the projections with a lightly 
 balanced lever recording on a slow kymograph. As soon as the oyster in a water bath at 
 a temperature between i8° and 20° C. had opened somewhat, the kymograph was started 
 and the temperature of the bath raised at the rate of 1° C. in about eight minutes. The 
 oysters remained fairly well open with brief periods of partial closure as the temperature 
 increased to about 22° C. At that point there invariably appeared in the three individ- 
 uals observed periods of maximum openness lasting as long as no disturbing factor inter- 
 vened. Suificient stimulus for partial closure, however, was likely to occur frequently. 
 A light tap on the table or water bath, a heavy step in the room, the slamming of a door 
 in a neighboring part of the building, or, indeed, any slight jar was surely registered by 
 some movement of the shell. As the temperature increased up to about 26° or 27° C, 
 the effect of these stimuli was much less marked. The oysters then maintained their 
 maximum openness very persistently. Between 27° and 30° a tendency to very slow 
 and incomplete opening after closure was noticeable, indeed no maximum openness was 
 seen. At about 30° or 31° C, the oysters closed tightly, even if no mechanical stimulus 
 was g^ven. 
 
 As the kymograph method served to detect movements of the shell not noticeable 
 to unaided observation and also slight openings of the shell not otherwise visible, these 
 experiments were an aid to planning and interpreting measurements of oxygen utiliza- 
 tion. They showed that below 19° C. and above 26° C. observations on the opened 
 oyster were impossible, that temperature must be maintained constant throughout the 
 experiment, and mechanical disturbances must be avoided as far as possible. A further 
 source of difficulty had also to be overcome. When the oyster excreted it closed vio- 
 lently, to drive the fecal matter out of the shell. If the position of the animal rendered 
 complete excretion difficult, closures were frequently repeated, and sometimes the oyster 
 shut up tightly. It was necessary, therefore, to lay the oyster in the desiccator tipped 
 so that the more concave side of the shell, where excretion occurs, would be lower than 
 the other. 
 
 In spite of all precautions, however, perfectly consistent results could not always 
 be obtained. Under the same or comparable conditions of temperature, oxygen content 
 of the water, and physical conditions, the same individual would sometimes in different 
 experiments give results disagreeing beyond the limits of the calculated, probable, experi- 
 mental error. Various observations make it seem likely that the nutritive condition 
 of the individual could account for some, at least, of these discrepancies. Thus, after 
 
OXYGEN REQUIREMENTS OP SHELI.FISH. 213 
 
 remaining at a high temperature (e. g., 24°-26° C.) for some time, the oxygen require- 
 ment at a slightly lower temperature would tend to be greater than if the shellfish had 
 been at a lower temperature before the experiment. If an oyster had been out of water 
 for some time before the measurement, more oxygen would be used, generally, than if 
 the specimen were left in the aquarium until the time of the experiment. After the 
 shellfish had been kept in the aquarium some weeks they tended to use less oxygen 
 than when taken recently from their native environment. Exceptionally an individual 
 would show a high utilization of oxygen out of proportion to previous measurements 
 and lasting for several days. As many of the interfering conditions as possible were, 
 of course, eliminated, but still it seemed necessary to make a considerable number of 
 experiments and draw conclusions only from averages. More than 350 measurements 
 were made under various conditions on three types of lamellibranchs — the oyster (Ostrea 
 virginica), the soft-shell or long clam {Mya arenaria), and the quahog or round clam 
 {Venus mercenaria). 
 
 RESULTS. 
 
 OXYGEN REQUIREMENTS OF THE OYSTER. 
 
 Three series of experiments, each made on a limited number of individuals, are sub- 
 mitted. Although the results can scarcely be taken to show any seasonal variation, 
 they are grouped, for convenience, according to the time they were carried out. In 
 table I are the results of measurements taken during July, 191 1; in table 11, those of 
 July and August, 1912; and in table ill are results obtained during the latter part of 
 August, 1912. 
 
 In the experiments of table i definite temperatures were not previously chosen and 
 carefully adhered to as in the later work. The results, therefore, are here grouped for 
 comparison as follows : All measurements taken at temperatures between 20° and 2 1 .3° C. 
 appear in one column, those at 21.5° to 23.5° C. in another, and those between 26° and 
 28° C. in a third. Where two or more experiments were made with one oyster at tem- 
 peratures within a given range the average of the results is placed in parentheses. . In 
 the last three columns are the averages of comparable experiments computed as the 
 decimilHgrams of oxygen used per hour per 100 grams of oyster. By weight of oyster 
 is meant in this and other tables not otherwise specified the weight in grams taken after 
 it was closed under water, wiped as dry as possible with a towel, and left to dry in the air 
 not more than half an hour. Such weighings were shown by duplication to be accurate 
 to within two-tenths of a gram. 
 
 In table 11 are the results of experiments performed at definite chosen temperatures 
 so controlled that the variation was not more than half a degree centigrade in any single 
 experiment. The first five columns of results show the decimilHgrams of oxygen used 
 per hour at five temperatures by nine oysters. The averages of all comparable experi- 
 ments are put in parentheses. The last five columns contain the averages, expressed 
 in decimilHgrams, of the oxygen used per hour per 100 grams of oysters. 
 
214 BULLETIN OF THE BUREAU OF FISHERIES. 
 
 Table I. — Oxygen Used by Oysters. 
 
 Note.— Figures in parentheses are averages of experiments under approximately uniform conditions. 
 
 Weight 
 
 Decimilligranis of oxygen used 
 per hour. 
 
 Average decimilUgrams of oxygen 
 per hour per 100 grams of oyster. 
 
 of whole 
 
 oyster. 
 
 At 20" to 
 
 At 21.5" to 
 23-5° C. 
 
 At 26° to 
 28° C. 
 
 At 20° to 
 21.3° C. 
 
 At 21.5* to 
 23.5° c. 
 
 At 26° to 
 28° C. 
 
 Grams. 
 
 43.0 
 
 56.6 
 85.0 
 
 106.0 
 
 113- 
 
 137.0 
 
 141. 
 
 
 5-6 
 9.0 
 7-8 
 6.8 
 (7.3) 
 
 II. 8 
 7.6 
 (9-7) 
 
 
 
 17.4 
 17.2 
 
 
 
 
 
 
 9.4 
 14.7 
 
 14.0 
 
 (13.7) 
 
 10. 1 
 15-6 
 (12.8) 
 
 14.6 
 
 12.7 
 13.6 
 
 19-3 
 18.8 
 (19..) 
 
 22.9 
 22.9 
 26.2 
 (24.0) 
 
 14-9 
 12. z 
 12.9 
 
 II. I 
 
 22.4 
 22.6 
 
 19.4 
 
 18.2 
 16. 1 
 (i7-i) 
 
 21.8 
 21. s 
 19.0 
 21. 2 
 (20.9) 
 
 19.0 
 18.0 
 
 (1S.5) 
 
 18.3 
 
 15- 1 
 16. s 
 
 13-1 
 
 
 
 
 
 
 
 
 
OXYGEN REQUIREMENTS OF SHELLFISH. 
 Table II. — Oxygen Used by Oysters. 
 
 -Figures in parentheses are averages of measurements under approximately uniform conditions. 
 
 215 
 
 Weight 
 «t whole 
 
 Decimilligrams of oxygen 
 
 used per hour. 
 
 Decimilligrams of oxygen used per hour per 100 
 grams. 
 
 
 
 
 
 
 
 
 
 
 
 oyster. 
 
 At 19.5° 
 to 20° C. 
 
 At 21° to 
 21.3° C. 
 
 At 22° to 
 
 22.5° c. 
 
 At 24° to 
 2A.sC. 
 
 At 26° to 
 26.3° C. 
 
 At 19.5° 
 
 t0 20°C. 
 
 At 21° to 
 21.5° c. 
 
 At 22° to 
 
 22.5° C 
 
 At 24° to 
 24.5^ c. 
 
 At 26° to 
 s6.s°C. 
 
 Grams. 
 
 42.0 
 
 ;. 6 
 9.8 
 
 (8.7) 
 
 12.3 
 
 13-8 
 
 (13.1) 
 
 10.3 
 
 13.9 
 
 (12.2) 
 
 14.6 
 
 13.4 
 14.9 
 II. 2 
 (l3-l) 
 
 20.; 
 
 31.0 
 
 .'9- I 
 
 34-8 
 
 31.3 
 
 51.0 
 
 II. 6 
 10. 7 
 II. 8 
 (11.3) 
 
 9-3 
 II. 4 
 9-5 
 6.2 
 (9-6) 
 
 u. 7 
 II. s 
 (II.6) 
 
 12.6 
 
 12.7 
 (12. 6s) 
 
 13-6 
 
 22.2 
 
 17.9 
 
 22.8 
 
 24-8 
 
 25. 7 
 
 66.5 
 
 .5-. 
 
 9.4 
 10.5 
 
 9.1 
 (11. 2) 
 
 16.0 
 9.9 
 
 16. I 
 14- 
 (14.0) 
 
 15.5 
 II. 8 
 (■3.7) 
 
 16.0 
 
 18.6 
 17.2 
 (17.9) 
 
 16.9 
 
 21.0 
 
 20.6 
 
 24. I 
 
 26.9 
 
 ;6.o 
 
 II. 5 
 14.0 
 
 (12.7) 
 
 13.9 
 15-3 
 14-2 
 (14. s) 
 
 ■53 
 
 12.8 
 (14.0s) 
 
 is.s 
 
 20. s 
 16.2 
 (17-5) 
 
 23- S 
 20.9 
 24.5 
 20. 7 
 (22.4) 
 
 16.7 
 
 19.0 
 
 18. s 
 
 23.0 
 
 29. S 
 
 97-4 
 uS. 
 
 13.4 
 
 13-7 
 17.S 
 (■S.7S) 
 
 14.6 
 
 
 
 
 13.8 
 
 
 
 1.9.5 
 
 
 17-9 
 25.9 
 18.6 
 18.4 
 (20.2) 
 
 25.9 
 19.8 
 (22. 8) 
 
 24.8 
 
 12.3 
 
 
 15- 7 
 
 17-8 
 
 19.4 
 
 
 
 147.0 
 
 16.0 
 19.4 
 (.7.7) 
 
 iS. 4 
 
 18.2 
 (18.3) 
 
 20.4 
 19.3 
 (19.8) 
 
 20.8 
 21.9 
 (21.3) 
 
 26.6 
 26.0 
 (26.3) 
 
 12. I 
 
 12.5 
 
 13-5 
 
 14. S 
 
 17.9 
 
 344.0 
 
 18. I 
 22.3 
 (20.2) 
 
 23.5 
 
 25- 7 
 (24.6) 
 
 34.6 
 
 30.0 
 26.1 
 24.0 
 (26. 7) 
 
 35- I 
 
 8-3 
 
 10. 1 
 
 12.3 
 
 II. 
 
 14.4 
 
 2&1.0 
 
 19.0 
 
 29.1 
 29.5 
 21.4 
 
 20.8 
 
 (25.2) 
 
 27.4 
 24.8 
 (26.1) 
 
 28., 
 30.7 
 (29.7) 
 
 37-0 
 
 7-3 
 
 9.6 
 
 10. 
 
 11-3 
 
 14. I 
 
 
 
 
 
 
 14. S 
 
 17.0 
 
 17.8 
 
 20. 
 
 22. S 
 
 
 
 
 
 
 
 In table in are the results of measurements at four chosen temperatures on four 
 oysters. These experiments were all done within a few days after the oysters were 
 taken from the beds and therefore serve to some extent as a control on the condition 
 of the oysters used in the other series. The first columns of results show the decimilli- 
 grams of oxygen used per hour at the designated temperatures. The averages of com- 
 parable experiments are put in parentheses. The figures in the next four columns are 
 obtained by computing the averages of the oxygen utilization per lOO grams of oyster. 
 In the next column is the weight, in grams, of the shell contents of each oyster when 
 dried to constant weight. The last four columns show average decimilligrams of oxygen 
 used per gram of dried substance. The figures in these columns were corrected for the 
 
2l6 
 
 BULI.ETIN OF THE BUREAU OF FISHERIES. 
 
 oxygen used by the shells. The shells of each oyster were at the end of the observations 
 carefully cleaned in sea water and then used for two or three measurements of their 
 oxygen-absorbing power at different temperatures. As these results were obtained 
 under the same conditions as those expressed in table in, they represent a fair estimate 
 of the oxygen absorbed by the shells during measurements with the intact oyster. There 
 is reason, as will be shown below, to believe that oxygen removed from the water in this 
 way is not utilized by the active tissues of the oyster. It seems reasonable, therefore, 
 to subtract the amount (measured or computed) of oxygen utilized by the shells from 
 that used by the whole oyster before computing the oxygen requirements per gram of 
 dried tissue. 
 
 Table III. — Oxygen Used by Oysters. 
 
 Note. — Figures in parentheses are averages of measurements under approximately uniform conditions. 
 
 
 Dccimilligrams oi oxygen used 
 per hour. 
 
 Averages of same per hour per 
 100 grams. 
 
 
 Average dccimilligrams used per 
 hour per gram of dried weight. 
 
 "Weight. 
 whole 
 oyster. 
 
 
 
 
 
 Weight, 
 dried 
 oyster. 
 
 
 At 
 20* to 
 20.5 "C. 
 
 At 
 
 22° to 
 
 2..5-C 
 
 At 
 
 24° to 
 
 24.5° C. 
 
 At 
 26° to 
 26.s°C. 
 
 At 
 
 20' to 
 
 20.5° C. 
 
 At 
 22° to 
 
 22.S°C. 
 
 At 
 24° to 
 24.5°C. 
 
 At 
 26' to 
 26.s°C. 
 
 At 
 20° to 
 
 20.s'*C. 
 
 At ' At 
 22° to 24° to 
 
 22.5°C 24.S°C. 
 
 At 
 
 26° to 
 26.5°C. 
 
 Grams. 
 
 
 
 
 
 
 
 
 
 Grams. 
 
 
 
 
 
 47-8 
 
 10. 6 
 
 12.2 
 14. I 
 (i3-i) 
 
 14.2 
 
 17. I 
 
 
 27.4 
 
 29. 7 
 
 35.7 
 
 1. 15 
 
 7.92 
 
 9.74 
 
 10.40 
 
 12.90 
 
 73-5 
 
 16.6 
 
 20- 
 
 ah 
 
 23.1 
 
 18.3 
 
 (20. r) 
 
 22.0 
 
 22.6 
 
 23.0 
 
 28.2 
 
 30.0 
 
 1.66 
 
 8.20 
 
 8.61 
 
 9.43 
 
 9.56 
 
 153- o 
 
 19- 4 
 
 22.4 
 
 21.4 
 21.7 
 
 24. s 
 
 (22. 5) 
 
 25-2 
 
 25-9 
 
 (25- 5) 
 
 12. 7 
 
 14.6 
 
 14. 7 
 
 16.6 
 
 2.36 
 
 5.98 
 
 6.78 
 
 6.56 
 
 7-15 
 
 173- o 
 
 23-5 
 
 24-5 
 
 29.2 
 
 39-0 
 
 13.6 
 
 14.2 
 
 17.3 
 
 2r. 2 
 
 3.64 
 
 3.49 
 
 4.00 
 
 4-53 
 
 6. 10 
 
 Average. 
 
 
 24.7 
 
 (24. 6) 
 
 30.8 
 (30. 0) 
 
 ,34-3 
 (36. 6) 
 
 
 
 
 
 
 
 
 
 
 17-5 
 
 19.7 
 
 21.9 
 
 25-3 
 
 17.8 
 
 20.3 
 
 23.5 
 
 25-9 
 
 
 6.41 
 
 7- 28 7. 73 
 
 8.94 
 
 A graphic representation of the oxygen utilization of oysters at different tempera- 
 tures is given on page 217. The ordinates represent decimilligrams of oxygen used 
 per hour and the abscissae are degrees Centigrade. The full lines represent measure- 
 ments on intact oysters. Curve i is constructed from the averages of the oxygen utiliza- 
 tion per hour per 100 grams in experiments on nine oysters as summarized in table 11. 
 Curve II is constructed from similar averages of experimental results on four oysters as 
 shown in table lu. Curve in is based on the same results used foi curve 11, but repre- 
 sents the averages of oxygen used pei hour per gram ot dried shell contents. The rela- 
 tionship between oxygen and temperature is apparently a simple one. The interrupted 
 lines represent measurements on empty oyster shells showing the decimilligrams of 
 oxygen used per hour by shells as recorded in table iv. Curves a, b, c, and d refer, 
 respectively, to shells weighing 47.8, 73.4, 153, and 161 grams. The effect of tempera- 
 ture on the three larger shells seems to be fairly constant; theii curves are parallel. 
 The discrepancy in the smallest shell may be due to experimental error as so few deter- 
 minations were made. 
 
OXYGEN REQUIREMENTS OF SHELLFISH. 
 
 217 
 
 26 
 
 20^ sr ^2^ £3' ^^4^ ^s' jss' zrc. 
 
2l8 BULLETIN OF THE BUREAU OF FISHERIES. 
 
 NON UTILIZATION OF OXYGEN BY CLOSED OYSTERS. 
 
 Since oysters can close absolutely water tight, it seemed possible that under such 
 conditions they would take in no oxygen. The very small oxygen requirements of 
 voluntarily closed individuals could not, however, be interpreted as proof of this because 
 when the oyster appears to be closed it may be slightly and invisibly open. This was 
 proved by graphic records. To insure closure throughout an observation it was neces- 
 sary, therefore, to use some artificial closing device. Several clamps were tried. An 
 ordinary surgeon's artery clamp was found to be most satisfactory. If clamps without 
 imperfections, carefully vaselined, were used, they did not appreciably rust during the 
 experiment and withdrew from the water only a small and constant quantity of oxygen. 
 As control experiments the oxygen absorption of empty shells of oysters about the same 
 size as the one observed was measured. The control shells were fastened together by a 
 clamp duplicating the one used on the oyster. Water had some access to the interior 
 of the empty shells through nicks in their edges. On their immersion in water all air 
 was driven from them. In many experiments controls were deferred until the same 
 oyster could be emptied and its shells used for control measurements. 
 
 The results of a number of determinations are given in table v. It is seen that in 
 every case the experiment and its control are in close agreement, as the difference is 
 within the limit of experimental error except in the case of the largest oyster used. 
 Even these differences, however, show a larger oxygen absorption by the empty shells 
 than by the closed intact oysters. That the slight oxygen disappearance does not repre- 
 sent a respiratory intake by diffusion through the shells is indicated not only by the 
 controls but by the obser^^ation that a two hours' exposure of the clamped oyster does 
 not cause twice the oxygen absorption observed during one hour. Thus in one experi- 
 ment a clamped oyster used 1.83 decimilligrams of oxygen in one hour, but 3.01 in two 
 hours, while another, which used 1.70 decimilligrams in one hour, required 2.80 for two 
 hours. 
 
 The explanation of the constant slight absorption of oxygen by clamped oysters 
 and empty shells was not positively determined, but would seem to lie in several 
 causes. Bacteria and various marine vegetative growths on the shells were first con- 
 sidered as possible oxygen users. Oyster shells that had been soaked 16 hours in 80 
 per cent alcohol and then carefully scrubbed and dried, did, indeed, show a diminished 
 oxygen absorbing capacity, in one case lowered from 5.25 decimilligrams per hour before 
 the alcohol treatment to 4.68 after it, and in another, from 3.08 to 2.34. This indicates 
 that foreign growths do not account for all the oxygen absorption, and, indeed, it was 
 found that the cleanest and most carefully sterilized shells took oxygen from the water. 
 
 An adsorption effect of porous substances on dissolved oxygen suggested itself as 
 another possibility. It was found that porcelain evaporating dishes about the size 
 of oysters showed equivalent oxygen absorbing powers. Corks had the same capacity. 
 Water containing medium sized corks lost 2.34 decimilligrams of oxygen per hour, while 
 in a control experiment water alone lost only 0.26 decimilligram, which is within the 
 limit of experimental error. 
 
OXYGEN REQUIREMENTS OF SHELLFISH. 
 Table IV. — Oxygen Absorbed by Empty Oyster Shells. 
 
 219 
 
 
 47-8 
 
 47.8 
 
 73-4 
 
 73-4 
 
 73-4 
 
 iSi 
 
 153 
 
 161 
 
 161 
 
 Temperature of experiment in decree! centigrade. . 
 
 
 J3.4 
 1.9 
 
 25-8 
 2.4 
 
 31.7 
 3-6 
 
 22.3 26.1 
 
 22.0 
 6.1 
 
 25-8 21. s 
 
 26. s 
 
 
 
 
 
 
 
 Table V. — Oxygen Absorbed by Closed Oysters. 
 
 Weight of 
 oyster. 
 
 Tempera- 
 ture of 
 experi- 
 ment. 
 
 ' Oxygen 
 
 used per 
 hour. 
 
 Description of control experiment. 
 
 
 °C. 
 
 Mgrjio. 
 
 
 45 grams . . . 
 Control 
 
 22.0 
 22.0 
 
 1.70 
 1.70 
 
 Empty shells of same oyster with artery clamp. 
 
 ■;o grams. . . 
 Control 
 
 22.0 
 22.0 
 
 ..83 
 1.83 
 
 Do. 
 
 66.5 prams. . 
 
 Control 
 
 Control 
 
 23-2 
 21.0 
 23- 2 
 
 2.04 
 1.92 
 2.58 
 
 Do. 
 
 Empty shells of oyster weighmg 45 grams with clamp. 
 
 66.5 grams. . 
 Control 
 
 20.5 
 20.5 
 
 i.4r 
 1.48 
 
 Empty shells of oyster weighing 51 grams with clamp. 
 
 128 grams.. 
 Control 
 
 20. s 
 
 20.5 
 
 1.79 
 1.92 
 
 Empty shells of same oyster with artery clamp. 
 
 147 grams. . 
 Control 
 
 20.5 
 20.5 
 
 1.74 
 J. 62 
 
 Do. 
 
 244 grams . . 
 Control 
 
 20.5 
 21.0 
 
 1.70 
 2-34 
 
 Do. 
 
 262 grams. . 
 Control 
 
 20.5 
 21.0 
 
 3-39 
 4.68 
 
 Do. 
 
 244 grams. . 
 
 27-5 
 
 3-47 
 
 
 128 grams. . 
 66.5 grams.. 
 76 grams. . . 
 
 27-5 
 
 27- S 
 27-5 
 
 2.36 
 2.49 
 2.80 
 
 Control experiments not made. 
 
 RESISTANCE OF OYSTERS TO LACK OF OXYGEN. 
 
 A series of experiments was undertaken to find out the minimum oxygen supply 
 that would maintain an oyster alive. The sea water surrounding an oyster in a vacuum 
 desiccator was as far as possible rendered oxygen free by boiling at room temperature 
 under diminished pressure for half an hour. It was found in two trials that sea water 
 alone when so treated and kept twelve hours in the closed desiccator still had an oxygen 
 content less than 0.5 of a part per million. An oyster kept under these circumstances 
 four days showed no ill effects. Another was kept thus three days, transferred to a 
 second desiccator of exhausted sea water, which was quickly again pumped out, and 
 was then kept four days further in the oxygen poor medium. The shells then had some 
 black deposits on them indicative of incipient anaerobic putrefaction. The sea water 
 on opening the desiccator was found absolutely oxygen free. The oyster, however, 
 seemed unimpaired, and after remaining in the aquarium some time was opened and 
 found apparently entirely normal. As each desiccator held about 1,200 c. c. and the 
 oxygen content of the water in each case was at the most 0.5 of a part per million, the 
 oxygen available to the oyster might be estimated as 1.2 milligrams plus the small 
 amount obtained during the transfer from one desiccator to the other. If we disregard 
 the latter source because the oyster was tight closed at the time, only 1.2 milligrams of 
 oxygen were used during seven days. 
 
220 
 
 BULLETIN OF THE BUREAU OF FISHERIES. 
 
 In another experiment an oyster was kept three days in the first desiccator full of 
 pumped-out water, three days in the second, two days in the third, two days in the fourth, 
 and two days in the fifth. By that time it was black and unable to close properly. 
 After a few hours in the aquarium it showed disintegration, so that twelve days of life 
 in oxygen-poor water proved fatal. Time and facilities for carrying out many of these 
 experiments were missing, although the seven-day experiment was practically dupli- 
 cated by one in which an oyster was kept in the same desiccator full of water six days 
 with no ill effects. That the fatal effect of a twelve days' exposure was not due to 
 insufficient renewal of the water was shown by control experiments in which several 
 oysters were kept in the same water during fourteen days while air was bubbled through 
 it. The oysters sur\dved this treatment uninjured. 
 
 OXYGEN REQUIREMENTS OF CLAMS. 
 
 Measurements on clams were made by the same method used for oysters. The 
 results of successful experiments are embodied in table vi. They show a general agree- 
 ment with measurements on oysters. The amount of oxygen used by ciams weighing 
 about 60 grams is somewhat higher per 100 grams than that used by an oyster of about 
 the same weight and observed at the same temperature. Computed per gram of dried 
 shell contents, however, the oxygen requirements of the clam seem somewhat smaller 
 than those of the oyster. Here, as with oysters, the amount of oxygen used is more 
 or less proportional to increase in the temperature, though sufficient data to show a sim- 
 ple relationship were not obtained. In this case, also, the oxygen requirement per gram 
 is less in the larger individual than in the smaller, again like the oyster. 
 
 Table VI. — Oxygen Used by Clams. 
 
 Note. — Figures in parentheses are averages of measurements under approximately uniform conditions. 
 
 Weight 
 whole 
 clam. 
 
 Decimilligrams of oxygen used 
 per hour. 
 
 Averages of same per hour per 
 100 grams. 
 
 Weight 
 dried 
 clam. 
 
 Average mgr/io used per hour 
 per gram, dried weight. 
 
 At 20° to 
 21° c. 
 
 At 22° to 
 22.5° c. 
 
 At 24° to 
 24.5° c. 
 
 At 20° to 
 
 2I°C. 
 
 At 22° to 
 
 22.5° C. 
 
 At 24* to 
 24.5^ C. 
 
 At 2o° to 
 21° C. 
 
 At 22° to 
 22.5° C. 
 
 At 24* to 
 24.5^ C. 
 
 Grams. 
 7.0 
 
 19. S 
 21.0 
 
 28.0 
 57-0 
 
 57- S 
 60.0 
 63.0 
 
 I. 2 
 
 C2-I) 
 
 5. 19 
 
 9-2 
 6.7 
 (7-9) 
 
 S. 2 
 
 II. 
 
 12.4 
 
 (ll-7) 
 
 
 
 =9-6 
 
 26.7 
 26.9 
 
 29-3 
 20.7 
 
 
 
 GrjjHJ. 
 
 
 
 
 9-7 
 
 15. 1 
 
 49-7 
 
 77-4 
 
 1.32 
 
 3.93 
 
 7-35 
 
 II. 4 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 17.2' 
 19. 1 
 
 30.0 
 
 30.0 
 31-9 
 
 52.2 
 
 3-97 
 
 
 4.34 
 
 7-5.'; 
 
 
 
 
 I-- 7 
 
 IS- 2 
 
 (16.4) 
 
 
 25-3 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
OXYGEN REQUIREMENTS OF SHELLFISH. 
 Table VII. — Oxygen Absorbed by Closed Quahogs. 
 
 221 
 
 
 ISO 
 
 150 
 
 91 
 
 91 
 
 246 
 
 246 
 
 150 a 
 
 ISO 6 
 
 91 » 
 
 
 
 24.0 
 •37 
 
 34.0 
 ■=S 
 
 24- 
 •38 
 
 23- 
 •25 
 
 24-3 
 •=3 
 
 23- 
 4^6o 
 
 23^0 
 
 4' 30 
 
 23^6 
 
 ^•43 
 
 23-5 
 2-95 
 
 
 
 a Voluntarily closed but not clamped. 
 
 & Measurements on empty shells alone. 
 
 OXYGEN ABSORPTION OF CLOSED CLAMS. 
 
 Only one experiment was made in this connection. A medium-sized clam was 
 closed by an artery clamp over the siphon end of the shells. As a control, empty shells 
 of an oyster of the same size similarly clamped were used. The live clam absorbed 2.68 
 decimilligrams of oxygen per hour at a temperature of 23.5° C, while the shell took 2.58. 
 This indicates that the clam, like the oyster, has little or no opportunity to obtain oxygen 
 when the shell is not open. Further observations incidentally made confirm this con- 
 clusion. A medium-sized clam which visibly failed to open throughout an experiment 
 to determine its oxygen requirements took only 2.44 decimilligrams of oxygen from the 
 water in an hour. Other similar results were obtained. 
 
 OXYGEN REQUIREMENTS OF QUAHOGS. 
 
 Great difficulty was experienced in measuring the oxygen utilization of quahogs, 
 because they seldom opened for any length of time under the conditions of experimen- 
 tation. As a result of this, only a few measurements that could be considered reliable 
 were obtained. It was found necessary to place the specimen in sea water in the desic- 
 cator a long time before the experiment, usually the night before, in order to have it 
 open at the time of observation. Handling or moving caused it to close and stay closed 
 for some hours. 
 
 The few successful observations showed a rather low oxvgen utilization. One 
 specimen weighing 91 grams used, at 24° C, 10. i decimilligrams of oxygen in one hour, 
 10.8 in another measurement, and 6.4 in a third. Another quahog, weighing 150 grams, 
 used, at 24° C, 7.8 decimilligrams per hour, and a large one (470 grams) used 22.4 deci- 
 milligrams per hour. Many other measurements were attempted, but owing to closure 
 soon after the beginning of observation were unreliable. The oxygen requirements in 
 proportion to the dried weight showed a still greater discrepancy in comparison with 
 similar computations for the oyster. The dried weights of the shell contents of the 
 first two quahogs observed were, respectively, 2.22 grams and 3.86 grams. The oxygen 
 used per hour and per gram of dried weight, then, was 4.10 decimilligrams for the first 
 and 2.21 for the second. This is less than half the amount of oxygen used bv ovsters 
 of comparable weight obser\'ed at the same temperature. To prop the shells open 
 seemed hardly worth while, because the oxygen utilization under such circumstances 
 would be abnormal on account of the resulting violent contractions of adductor muscles. 
 It seemed best, therefore, to be content with the conclusion that under the circumstances 
 of these experiments quahogs used only a small quantity of oxygen. 
 
222 
 
 BUIylvETIN OF THE BUREAU OF FISHERIES. 
 
 UTILIZATION OF OXYGEN BY CLOSED OUAHOGS. 
 
 Clamping these shells as in the experiments described for oysters showed that closed 
 quahogs used no oxygen. Their very smooth shells apparently took almost no oxygen 
 from the water. With various sizes of quahogs clamped and observed at 24° C, results 
 were obtained as follows: 0.37, 0.25, 0.38, 0.23, and 0.25 decimilligram of oxygen per 
 hour. The empty shells, considerably broken in the process of opening, used a 
 distinctly larger amount of oxygen than did the closed intact animal. The small amounts 
 of oxygen taken up under these conditions are no more than would disappear from the 
 sea water with a clamp in it. 
 
 It was clearly shown, however, that voluntarily closed quahogs did take up appre- 
 ciable quantities of oxygen. In observations where the shells were apparently quite 
 closed, various medium and large sized specimens took up, at 24° C, 2.9, 6.1, 4.6, and 
 4.3 decimilligrams of oxygen per hour. It would seem, then, that when voluntarily 
 closed they do not remain shut absolutely tight, but take in small amounts of water 
 through an aperture too narrow to be visible to the naked eye. The results are sum- 
 marized in table vii. 
 
 CONCLUSIONS. 
 
 1. Oysters of medium sizes, at temperatures between 19° and 28° C, used from 7 to 
 35 decimilligrams of oxygen per hour per 100 grams of entire weight. The amount varies 
 with the temperature, so far as experiments show, according to simple relationship, so 
 that the curve approximates a straight line. It is proportionally less for larger speci- 
 mens. The oxygen utilization is, however, exceedingly variable, depending on a variety 
 of conditions, most of which probably affect the openness of the shell. 
 
 2. Oysters when tightly closed take no oxygen from the surrounding water; at 
 least, no more than is taken by empty shells. 
 
 3. Oysters show considerable resistance to lack of oxygen. Only exposure for more 
 than a week to water containing very small quantities of oxygen proved fatal. This 
 indicates that any conditions causing temporary decrease in the available oxygen are not 
 a significant factor in oyster culture. 
 
 4. The common clam (Mya arenaria) shows a higher oxygen requirement than the 
 oyster. This seems surprising, in view of the fact that clams so often exist in muds 
 where oxygen-consuming putrefactions are going on. The oxygen requirements of 
 clams and oysters in proportion to their dried weights are about equal. 
 
 5. Both clams and quahogs (Vcmts merccnaria) use no oxygen from the water when 
 tightly closed, but the quahog takes up oxygen while slightly and invisibly open. 
 
 6. The oxygen requirements of the quahog are, under the conditions of these' experi- 
 ments, conspicuously low. 
 
UBRARVOFCOHGJ^S