290 I.C. POTTER ET AL.

© 1997 WILEY-LISS, INC.

JEZ 798

Oxygen Uptake and Carbon Dioxide Excretion bythe Branchial and Postbranchial Regions of Adultsof the Lamprey Geotria australis in Air

I.C. POTTER,* D.J. MACEY, AND A.R. ROBERTSSchool of Biological and Environmental Sciences, Murdoch University,Murdoch 6150, Western Australia, Australia

ABSTRACT O2 uptake and CO2 excretion by the branchial and postbranchial regions of adultsof the lamprey Geotria australis have been measured in humidified air at 15 and 5°C. At 15°C,the mean standard V·O2 for whole animals was 31.9 µl⋅gm–1⋅hr–1, which is similar to the interpo-lated V·O2 in water at the same temperature and time of year. The corresponding mean standardV·CO2 was 25.2 µl⋅gm–1⋅hr–1, producing an RQ of 0.79. The branchial region was responsible for~87% of O2 uptake and ~80% of CO2 excretion, which indicates that the gills of lampreys retaintheir integrity in air and thereby facilitate gas exchange. The continuous pumping of the bran-chial chamber would also facilitate gas exchange across the gills. The RQ is far higher in thepostbranchial than branchial region, i.e., 1.26 vs. 0.72. The proportionately greater excretion ofCO2 than uptake of O2 by the postbranchial than branchial region is presumably related to acombination of the greater capacitance of tissue for CO2 than O2 and the presence of a thickertissue barrier in the skin of the trunk and tail than in the lamellae of the gills. At 5°C, the meanstandard V·O2 and V·CO2 for whole animals declined markedly to 13.1 and 13.5 µl⋅gm–1⋅hr–1, respec-tively. The corresponding rise in RQ from 0.79 at 15°C to 1.03 at 5°C implies that aerobic metabo-lism now utilizes solely carbohydrate, rather than lipid and some carbohydrate. The transfer tosolely carbohydrate metabolism at 5°C may be triggered by a need to supplement aerobic metabo-lism with anaerobic metabolism to compensate for an apparent shortfall in oxygen uptake producedby inadequate ventilation of the gills. J. Exp. Zool. 278:290–298, 1997. © 1997 Wiley-Liss, Inc.

*Correspondence to: I.C. Potter, School of Biological and Environ-mental Sciences, Murdoch University, Murdoch, Western Australia6150. Email: i-potter@possum.murdoch.edu.au

Received 10 September 1996; Revision accepted 30 January 1997

The Agnatha or jawless vertebrates are repre-sented in the contemporary fauna only by the lam-preys and hagfishes (Hardisty, ’82). The life cycleof the anadromous species of lampreys containsdiscrete larval and adult trophic phases. The lar-vae (ammocoetes) are microphagous and live inthe soft substrata of streams and rivers (Potter,’80), whereas the adults are marine and parasitic,feeding mainly on the blood and or muscle of te-leost fishes (Potter and Hilliard, ’87). At thecompletion of their trophic phase, the adults re-enter rivers and embark on a migration to theirupstream spawning areas, which, in the case ofthe southern hemisphere lamprey Geotria austra-lis, lasts for about 15 mo (Potter et al., ’83). Dur-ing this spawning run, the adults sometimes leavethe water at night and move along the banks ofthe river and are thus able to bypass dams andother obstacles to their upstream movement. Re-cent work has shown that ammocoetes and adultsof G. australis can survive out of water for ex-tended periods without apparent discomfort (Pot-ter et al., ’96a,b). An ability to respire out of water

would be crucial to ammocoetes, if they becometemporarily stranded in their burrows above thewater line following marked declines in water leveland to adults when they are moving over land.

The standard V·O2 of adult G. australis at 15°Cin November and December is the same in air asin water (cf. Macey et al., ’91; Potter et al., ’96b).The ability to respire in air suggests that a con-siderable volume of O2 is taken up across the skin,a process that could be facilitated by the well-de-veloped capillary network that is present in thedermis of the adults of this species (Potter et al.,’95). However, the branchial chamber continuesto beat when adult G. australis are out of water,which suggests that the gills play an importantrole in O2 uptake when these lampreys are in air(Potter et al., ’96b).

The first aim of the present study was to deter-

THE JOURNAL OF EXPERIMENTAL ZOOLOGY 278:290–298 (1997)

O2 UPTAKE AND CO2 EXCRETION BY LAMPREYS IN AIR 291

mine the V·O2 and V·CO2 for both the branchial andpostbranchial regions of adult G. australis in airat 15 and 5°C. This enabled us to calculate theRQ for these two regions and for the whole ani-mal and to determine both the relative roles ofthese regions in gas exchange and whether lam-preys build up an oxygen debt at either of thesetwo temperatures. Simultaneous measurementswere made of the respiratory potentials to ascer-tain whether the branchial chamber always beatswhen lampreys are in air and to determine therate of any such beating during periods of inac-tivity, i.e., when O2 consumption can be regardedas standard (sensu Beamish and Mookerhjii, ’64).The results of the above studies would indicatewhether the gills of adult lampreys play an im-portant role in respiration in air.

MATERIALS AND METHODSCollection and maintenance of animals

Adult Geotria australis were collected duringOctober and November, as they were migratingup rivers in southwestern Australia. They weretransported to the laboratory where they weremaintained in 150-L tanks. The water tempera-ture and light-dark regimes were modified weeklyso that they paralleled the trends taking place inthose variables in the field. Lampreys were sub-sequently acclimated to the experimental watertemperatures of 15 ± 1 and 5 ± 0.5°C for at least

1 wk prior to experimentation. Experiments werecarried out from June to August, using two maleand four female lampreys at the former tempera-ture and one male and four female lampreys atthe latter temperature.

RespirometerA flow-through respirometer (Fig. 1) was used

to measure V·O2 and V·CO2 separately in the bran-chial region (head + pharyngeal region) andpostbranchial region (trunk + tail) of lampreys inair. The animal chamber of the respirometer con-sisted of a clear perspex tube, 860 mm in lengthand 33 mm in diameter. It was cut in two at apoint 250 mm from its anterior end to allow theinsertion of a dividing flange, constructed fromimpermeable latex, in which a central aperturehad been cut to allow the flange to fit securelyaround the animal. The small anterior and largerposterior sections of the chamber were then boltedtogether. The anterior section of the chamber waslined with electrodes, spaced at 15-mm intervals,to enable a recording to be made of the strongelectric potentials, that are produced during thecontraction of the branchial basket of adult lam-preys (Claridge et al., ’73). These electrodes wereconstructed of 0.5-mm-diameter silver wire, theends of which penetrated the walls of the animalchamber via airtight seals (Fig. 1).

At the commencement of each experiment, a

Fig. 1. Diagram of the respirometer used for measuring V·O2 and V·

CO2 in the branchialand postbranchial regions of adult Geotria australis in air.

292 I.C. POTTER ET AL.

lamprey was weighed to the nearest 1g and care-fully introduced into the chamber and placed in aposition whereby the latex flange formed a sealaround the region of the body that lies immedi-ately behind the seventh and most posterior pairof branchiopores (Fig. 1). Sections of fine nylonmesh were then inserted into either end of thechamber to discourage the lamprey from movingeither forward or backward along the chamber,thereby helping ensure that the flange surround-ing the lamprey remained in place. Air from a cyl-inder of compressed air was passed, at 50 ml·min–1,through a glass frit immersed in a 500-ml cylin-der of water. A series of taps then allowed thishumidified air to be passed into either the ante-rior section of the animal chamber (containing thebranchial region of the lamprey) or posterior sec-tion of the animal chamber (containing the post-branchial region of the lamprey) or through abypass around the animal chamber, the last al-lowing baseline gas levels to be measured. Exhal-ant air was then directed through a cold finger(–70°C) to remove water vapor and a copper equili-bration coil to return the air to room tempera-ture, before finally passing through a Binos C CO2analyzer and then a Servomex 570A O2 analyzer.The polyethylene tubing employed in the respirom-eter was thick walled and had a low permeabilityto both O2 and CO2. When the bypass was in use,room air was supplied to both sections of the ani-mal chamber via an auxiliary humidifier.

The voltage outputs from the CO2 and O2 ana-lyzers were connected to an IBM compatible com-puter via the RS232 interfaces of a Thurlby 1740Aand Myong MY-77 digital multimeter, respectively.The computer recorded the percent volume of eachgas in the sample air at 1-min intervals, a valuecalculated from a mean of 10 readings taken overa 10-sec period. These values were then convertedto µl·gm–1·hr1 (STP), using the animal weight andenvironmental values recorded at the beginningof each experiment (pressure to the nearest 0.01kPa and temperature to 0.1°C). A real-time plotof these values was constructed to allow the timeswhen gas levels had stabilized to be readily deter-mined. O2 levels within the chamber never fell be-low 95% of normal atmospheric levels (20.95%). Theelectric potentials produced by branchial contrac-tions were picked up by the electrodes located withinthe anterior region of the animal chamber and wererecorded at intervals using a Washington Physio-graph Model 400 MD 2R, thereby enabling the rateof branchial beating to be determined.

Because adult lampreys, in light, attempt to

move into areas that provide cover (Potter et al.,’83), all experiments were conducted in a dark-ened room to minimize the likelihood of suchmovements occurring. Individual experimentswere performed for at least 6–8 hr, to ensure thatV·O2 had declined to a relatively constant and thusstandard level (Potter et al., ’96b). Standard V·O2and V·CO2, which were calculated during this lat-ter ‘‘constant’’ period, represent the rate of O2 up-take and CO2 excretion over any consecutive10-min period, during which gas exchange was atits minimal level. V·O2 and V·CO2 of both the bran-chial and postbranchial regions, as well as of thewhole animal, are expressed in terms of the totalbody weight of the whole animal.

Preliminary experimentA preliminary experiment was conducted to con-

firm that the latex flange, used to divide the twosections of the animal chamber, was essentiallyimpervious to O2 and CO2 and formed a suffi-ciently tight fit around the lamprey to prevent ei-ther of these gases leaking between the twosections of the animal chamber. A dead lampreywas placed in the animal chamber, with the flangelocated just posterior to the seventh pair ofbranchiopores. Sample air was passed through theposterior chamber at 50 ml·min–1, and the levelsof O2 and CO2 in the air passing out of that sec-tion of the chamber were recorded. Humidifiedroom air and 100% CO2 were passed alternatelyinto the anterior section of the animal chamberat flow rates of 80–100 ml·min–1. Because therewas no change in the volumes of O2 and CO2 inthe sample air passing out of the posterior sec-tion of the animal chamber, the flange did not per-mit measurable levels of these gases to passbetween its two sections.

All experimental procedures were approved bythe Murdoch University Animal ExperimentationEthics Committee.

RESULTSExperiments at 15°C

Despite fitting a flange around the anteriormostregion of its trunk, i.e., in the region immediatelybehind the seventh and most posterior branchio-pore on each side of the body, the adult lampreybehaved in the same way as when it was intro-duced into the individual chamber without aflange (Potter et al., ’96b). Thus, it often used itssuctorial disk for attachment to the inside wall ofthe animal chamber and remained in the same

O2 UPTAKE AND CO2 EXCRETION BY LAMPREYS IN AIR 293

position for lengthy periods. Furthermore, the V·O2likewise declined initially, before leveling off af-ter about 4–6 hr.

The pattern of traces for V·O2 and V·CO2 by thebranchial and postbranchial region of a lampreywhich, after an acclimation period of 6 hr, re-mained motionless for 56 min, and then movedslightly on three occasions during the remaining94 min of the experimental period, are shown inFigure 2. During the two most pronounced of thosebrief movements, which were accompanied by apronounced increase in the amplitude of beatingof the branchial chamber, the V·O2 of the branchialregion rose sharply to 79.9 and 53.0 µl⋅gm–1⋅hr–1

and then rapidly returned to a level similar tothat prior to activity. Both of these pronouncedspikes in V·O2 were accompanied by a sharp butless elevated spike in V·CO2. This difference in el-evation of the spikes for V·O2 and V·CO2 probably re-flects the fact that the amount of CO2 present inthe branchial chamber prior to exhalation is lessthan the amount of O2 that enters during inhala-tion. The relatively small amount of CO2 in thebranchial chamber is due to the relatively very highdiffusion gradient of this gas to the environment.Standard V·O2 and V·CO2 in the branchial region ofthis animal were 30.7 and 23.6 µl⋅gm–1⋅hr–1, result-ing in an RQ of 0.77. The rate of branchial pump-ing ranged from 35 to 56 beats/min, with thegreatest values being recorded during and imme-diately after the very short bursts of activity. Inthe postbranchial region, the standard V·O2, i.e.,3.4 µl⋅gm–1⋅hr–1, was not as great as standard V·CO2,i.e., 4.8 µl⋅gm–1⋅hr–1 (Fig. 2). The RQ in this re-gion was 1.41. Standard V·O2 and V·CO2 of the whole

animal were 34.1 and 28.4 µl⋅gm–1⋅hr–1, respectively,producing an RQ of 0.83.

Standard V·O2 and V·CO2 for whole animals rangedfrom 27.1 to 37.6 µl⋅gm–1⋅hr–1 and from 22.0 to 31.2µl⋅gm–1⋅hr–1, respectively, with the values for thetwo males lying within the range covered by thoseof the four females. The mean values for stan-dard V·O2 and V·CO2 were 31.9 and 25.2 µl⋅gm–1⋅hr–1,respectively (Table 1). The mean RQ for all ani-mals was 0.79. Mean standard V·O2 and V·CO2 of thebranchial region, i.e., 27.8 and 20.1 µl⋅gm–1⋅hr–1,respectively, were 6.8 and 4.0 times greater thanthose of the postbranchial region. The RQs inthese two regions were 0.72 and 1.26 respectively(Table 1). During the protracted quiescent peri-ods, ventilatory frequencies ranged from 34 to 74beats/min, producing a mean ± SE of 57.4 ± 9.4beats/min.

Experiments at 5°CThe traces for V·O2 and V·CO2 of one of the lam-

preys at 5°C are shown in Figure 3. V·O2 remainedabove V·CO2 in the branchial region during most ofthe experimental period, whereas V·CO2 was alwaysgreater than V·O2 in the postbranchial region. Al-though this lamprey did not show the occasionalsharp spikes in V·O2 that characterized lampreysat 15°C, such spikes were exhibited by three ofthe other lampreys at 5°C.

The mean standard V·O2 and V·CO2 of whole lam-preys at 5°C were 13.1 and 13.5 µl⋅gm–1⋅hr–1, re-spectively, the resultant RQ being 1.03 (Table 1).Although the mean standard V·O2 was greater thanthe mean standard V·CO2 in the branchial region,i.e., 10.3 vs 9.0 µl⋅gm–1⋅hr–1, the reverse situationpertained in the postbranchial region, where therespective values were 2.8 and 4.5 µl⋅gm–1⋅hr–1.These differences account for the far higher meanRQ in the postbranchial (1.91) than branchial(0.88) region. The RQ for the postbranchial re-gion was far more variable at 5 than 15°C, whichaccounts for the fact that, at 5°C, the mean of theRQs (1.91) is greater than that which would bederived from the mean values for V·O2 and V·CO2,i.e., 1.61. The mean ventilatory frequency ± SEwas 43.8 ± 2.1 beats/min.

DISCUSSIONO2 uptake and CO2 excretion of

whole animals at 15°C

The mean standard V·O2 that we recorded foradult G. australis in air at 15°C from June to Au-gust is similar to the rate interpolated for adult

Fig. 2. Traces showing V·O2 and V

·CO2 of the branchial and

postbranchial regions of an adult of Geotria australis at 15°C.

294 I.C. POTTER ET AL.

G. australis in water at the same temperature andtime of year (Macey et al., ’91). The similarity be-tween V·O2 in air and water parallels the situationfound in certain amphibious fishes (Gordon, ’95).Because adult G. australis can also survive out ofwater for many hours at 15°C, without apparentdiscomfort (Potter et al., ’96b), it appears unlikelythat they build up a significant O2 debt. Such aconclusion is consistent with the similarity be-tween their RQ and that which would be antici-pated for a lamprey at this stage of its life cyclein water (see below). Because neither O2 uptakenor CO2 excretion appear to be limited, our CO2to O2 ratio for the resting animal at 15°C is thusconsidered to represent closely the true respira-tory quotient (RQ), i.e., the ratio of CO2 producedto O2 consumed during tissue metabolism (Bar-tholomew, ’82), rather than just the respiratoryexchange ratio (RER), i.e., the ratio of CO2 re-leased at the respiratory surfaces to O2 consumed(Martin, ’93). A comparable situation has recentlybeen recorded for two intertidal amphibious fishes(Steeger and Bridges, ’95).

Because adult lampreys do not feed during theirspawning run and thus have to rely to a large

extent on stored lipid as their main energy source(Moore and Potter, ’76; Beamish et al., ’79; Birdand Potter, ’83), such animals, during this phasein the life cycle, might be expected to have an RQof about 0.71 (Schmidt-Neilsen, ’90). The fact thatthe mean RQ for whole adult lampreys was 0.79and thus higher than 0.71 suggests that some car-bohydrate is also being catabolized. The RQ foradult G. australis in air lies within the range ofRERs recorded for a number of intertidal fishes(Bridges, ’88; Martin, ’95).

O2 uptake by the branchial region at 15°COur data demonstrated that ~87% of the O2

taken up by adult G. australis in air at 15°C oc-curs across the anterior region of the body. Be-cause the dorsal surface of the area in front ofthe branchial chamber is underlain by the carti-laginous cranium and the oral disc is covered bykeratinized teeth, it seems highly likely that thevast majority of the O2 taken up in this anteriorsection of the body occurs predominantly acrossthe gills. This conclusion is consistent with thefact that the branchial region underwent pro-nounced rhythmical contractions and expansionsat all times throughout the experiments, demon-strating that air was being pumped into and outof the seven pairs of branchial pouches, throughtheir respective branchiopores (see Randall, ’72for diagram showing the pattern of tidal flow intoand out of the branchial chamber). Because theskin covering the lateral parts of the branchialregion surrounding the branchiopores is highlyvascularized, it is also possible that some of theO2 taken up in this region occurs cutaneously.

The high contribution made by the branchialregion to the total V·O2 of lampreys in air, and themaintenance of oxygen consumption at a levelsimilar to that in water, contrasts with the situa-

TABLE 1. Standard V·

O2 and V·

CO2 at 15 and 5°C for adult G. australis and also separately for theirbranchial and postbranchial regions1

Whole animal Branchial region Postbranchial region Weight V·O2 V·CO2 RQ V·O2 V·CO2 RQ V·O2 V·CO2 RQ (gm)

15°CMean 31.9 25.2 0.79 27.8 20.1 0.72 4.1 5.0 1.26 173SE 1.6 1.5 0.02 1.6 1.4 0.02 0.3 0.4 0.10 6% of total 87.1 79.8 12.9 19.8

5°CMean 13.1 13.5 1.03 10.3 9.0 0.88 2.8 4.5 1.91 163SE 0.9 0.6 0.04 0.7 0.6 0.05 0.7 0.4 0.49 8% of total 78.6 66.7 21.4 33.3

1All rates are expressed in terms of the whole body weight of the animal and as µl·gm–1·hr–1. The percentage contribution of O2 uptake andCO2 excretion to their respective totals for the whole animal are also given. Six lampreys were used at 15°C and five at 5°C.

Fig. 3. Traces showing V·O2 and V

·CO2 of the branchial and

postbranchial regions of an adult of Geotria australis at 5°C.

O2 UPTAKE AND CO2 EXCRETION BY LAMPREYS IN AIR 295

tion recorded for the European eel, which has asimilar body shape to an adult lamprey. When thatteleost was transferred from water to air, the con-tribution made by the branchial region to O2 up-take declined from 85–90% to ~33%, and theoverall O2 consumption of the animal was reducedby about half (Berg and Steen, ’65). Lepidogalaxiassalamandroides, a species that lives in ephemeralpools in the same southwestern corner of Austra-lia as G. australis, obtains only ~17% of its O2 viathe gills when in air (Martin et al., ’93). The rela-tively low contribution made to O2 uptake by thebranchial region of the above teleosts is presum-ably related to the tendency for the gills of mostteleosts to collapse in air and thus not to be welladapted for aerial gas exchange (Randall et al.,’81). However, the tendency for such collapse tooccur in air is to a large extent overcome in cer-tain amphibious fishes by the presence of support-ing cartilaginous rods in the gills (Graham, ’73).The ability of the gills to maintain their struc-ture is also enhanced by a considerable reductionin gill area, which is responsible in part for thefact that the gills of these amphibious fishes ac-count for far less of their total oxygen uptake inwater than is typically the case with teleost fishes(Martin, ’95), and also with adult lampreys in air.

When considering the role of the gills in respi-ration in air, it is important to recognize that, incontrast to the situation in teleost fishes, the bran-chial arches of adult lampreys lie outside the gills,and the gills themselves are located in pouches(Lewis and Potter, ’76; Burggren et al., ’85). Thegill lamellae of adult lampreys may thus tend toretain their integrity to a greater extent in airthan is usually the case with teleosts and therebybe a more efficient facilitator of gas exchange un-der these conditions. Unfortunately, attempts toblock the external branchiopores in a variety ofways all caused such distress to the lampreys thatwe did not consider it feasible to use this type ofapproach to confirm that the majority of O2 takenup by the branchial region of adult G. australisin air occurred via the gills.

O2 uptake by the postbranchialregion at 15°C

Although the surface area of the postbranchialregion of the body of adult lampreys is relativelysmall compared with that of the area covered bythe gills, ~13% of the O2 taken up by the animalstill enters the body across the skin in this re-gion. This latter value is slightly less than the18% estimated by Korolewa (’64) for the contri-

bution made by this region to the uptake of O2 byLampetra fluviatilis in water.

The contribution made to total O2 uptake by thepostbranchial region of adult G. australis, andthus by cutaneous transport within that region,is far lower than is typically found among am-phibious teleost fishes in air. The contributionsmade by the skin to the uptake of O2 in air byamphibious fishes, such as mudskippers, typicallylie between 43 and 76% (Teal and Carey, ’67; Gra-ham, ’73; Tamura et al., ’76; Pelster et al., ’88;Martin, ’95). In the case of amphibious mud-skippers, a very well-developed system of bloodvessels lies within or immediately below the epi-dermal cells, resulting in the presence of a verythin air-blood barrier (Yokoya and Tamura, ’92).Because O2 has a low solubility in biological tis-sues, such an arrangement would be more effi-cient for transporting O2 across the skin thanwould be the dermal capillary network of adultG. australis, which is not as well developed andlies below the epidermis and thus further belowthe body surface (Potter et al., ’95). This differ-ence would help account, at least in part, for theproportionately far greater uptake of O2 that oc-curs across this part of the body in the above te-leosts than is the case in adult G. australis.Furthermore, the gill area of adult lampreys iscomparable with that of most active teleosts(Lewis and Potter, ’76), whereas that of many am-phibious fish is reduced, which helps mitigateagainst water loss in air (Bridges, ’88). The rela-tively small amount of O2 taken up cutaneouslyby adults of G. australis in air and of L. fluviatilisin water (Korolewa, ’64) suggests that much ofthe O2 obtained in this way may be used for themetabolically demanding processes that occur inthe skin, such as the transport of ions and theproduction and secretion of mucus (Feder andBurggren, ’85). If this is the situation in adult G.australis, it would parallel that found in certainfreshwater teleosts, in which the O2 taken up bythe skin is not used by other organs (Kirsch andNonnotte, ’77; Nonnotte, ’81).

RQs for branchial and postbranchialregions at 15°C

The RQs determined for the branchial andpostbranchial regions of the body, i.e., 0.72 and1.26, respectively, emphasize that the ratio of CO2excretion to O2 uptake is far greater in the latterof these two regions. Furthermore, the formervalue is very much closer to the overall RQ forthe whole animal. Because at least most of the

296 I.C. POTTER ET AL.

O2 taken up by the branchial region presumablyoccurs across the gills, such transport will be fa-cilitated by the very thin air-blood pathway in thegill lamellae of lampreys (Youson and Freeman,’76; Lewis and Potter, ’82). In contrast, the dis-tance between the surrounding air and underly-ing blood vessels in the trunk region (Potter etal., ’95) is far greater than in the lamellae. Thisfeature, together with the far greater capacitanceof biological tissues for CO2 than O2 (Feder andBurggren, ’85), would then account for the greatertransfer of CO2 than O2 across the body surface.Korolewa (’64) also found that, in adult L. fluvia-tilis in water, the RQ was greater for the skinthan the gills, thereby paralleling the situationthat exists with adult G. australis in air. The rela-tively greater importance of the skin in CO2 re-lease than in O2 uptake is typical of vertebratesin which there is cutaneous gas exchange (Federand Burggren, ’85). However, this situation doesnot pertain with L. salamandroides, in which theRER for its anterior and gill region was 1.2 andthus far higher than the 0.57 recorded for the pos-terior region (Martin et al., ’93).

O2 uptake and RQs at 5°CThe following comparisons between V·O2, RQ, am-

plitude of branchial beating, and behavior of lam-preys in air at 5 and 15°C, and between the V·O2and behavior of lampreys in air and water,strongly indicate that adult G. australis becomestressed in air at the lower temperature and alsochange the type of metabolism used for energygeneration at that temperature. The mean stan-dard V·O2 of adult G. australis in air at 15°C inNovember and December (Potter et al., ’96b) isidentical to that recorded in water at the sametemperature and time of year. The fact that themean standard V·O2 of adult G. australis deter-mined in air at 15°C during the following Juneand July in the present study is ~27% greaterthan that recorded in water at the same tempera-ture in May is consistent with the fact that theV·O2 of adult lampreys increases markedly duringthe later stages of their upstream migration(Claridge and Potter, ’76; Macey et al., ’91). How-ever, even though the mean standard V·O2 of adultG. australis in air at 5°C was measured in Au-gust, it was still essentially the same as in waterin May, and thus had not shown the same type ofrise that was exhibited by V·O2 at 15°C. Further-more, the mean standard V·O2 of adult G. austra-lis in air at 5°C is 2.4-fold lower than that recordedat 15°C, which, on the basis of the Q10 values for

V·O2 in water (Macey et al., ’91), is slightly greaterthan would have been expected with this 10°C de-cline in temperature. The decline in V·O2 was alsonearly twice as great in the branchial region asin the postbranchial region, i.e., 2.7 vs. 1.5 times.Moreover, although electrical potentials producedby the muscular contractions of the branchial bas-ket could always be detected at 5°C, these contrac-tions were often only just detectable visually,thereby contrasting markedly with the situation at15°C, where such contractions were very pro-nounced. It is thus suggested that, at 5°C, adult G.australis are unable to pass sufficient air in throughtheir small branchiopores (for diagram of bran-chiopores see Fig. 4 in Randall, ’72) to ventilate thegills with sufficient oxygen to maintain normoxicconditions in the branchial chamber and, as a con-sequence, the branchial chamber becomes slightlyhypoxic. The results and observations at the twotemperatures account for the fact that adult G.australis usually began to show distress whenthey had been out of water for more than 10 hrat 5°C, a feature that would probably have cul-minated in death within a few more hours,whereas they still did not show any signs of stressafter being in air for 24 hr at 15°C (see also Pot-ter et al., ’96b). The stress exhibited by adult G.australis in air at 5°C contrasts with the situa-tion in water at this temperature, where theselampreys can survive for long periods without ap-parent discomfort (Macey et al., ’91).

If adult G. australis cannot obtain all of theirenergy requirements from aerobic metabolism inair at 5°C, they must presumably rely to someextent on anaerobic metabolism and build up asmall oxygen debt. Should this be the case, itwould parallel the situation with the Europeaneel in air, which likewise maintains its V·O2 at aconstant level for several hours and, in this case,has been shown also to undergo lactic acidosis overthis period. In the context of the possibility thatlactic acidosis occurs in adult G. australis in airat 5°C, it is worth noting that the work of Tufts(’91) has shown that such lactosis occurs in thearterial blood of adult Petromyzon marinus dur-ing exhaustive exercise.

The marked rise that occurs in the RQ of adultG. australis between 15 and 5°C, i.e., 0.79 to 1.03,indicates that, at low temperatures, the energyfor aerobic metabolism comes from oxidation ofcarbohydrate, rather than from lipid and carbo-hydrate, as is apparently the case at higher tem-peratures (see earlier). This switch to entirelycarbohydrate metabolism may reflect a response

O2 UPTAKE AND CO2 EXCRETION BY LAMPREYS IN AIR 297

to the respiratory stress to which adult lampreysappear to be exposed at low temperatures andwhich consequently requires the use of anaerobicas well as aerobic metabolism. This view is basedon the fact that such a switch has the advantagethat carbohydrate can be used to produce energyboth anaerobically as well as aerobically, whereaslipid can only be used aerobically. The apparentlygreater ability of adult G. australis to be able tosurvive using only aerobic metabolism for meet-ing its ‘‘standard’’ oxygen requirements in air at15°C than it can at 5°C, would account for thefact that these lampreys are generally not ob-served undergoing nocturnal movements out ofwater until they have been on their spawning runfor several weeks and early nightfall air tempera-tures have by then risen to ca 15°C.

ACKNOWLEDGMENTSWe thank D. Morgan, L. Stonell, and G. Sarre

for collecting lampreys and P. Withers for the loanof his CO2 analyzer. Constructive criticisms ofearly drafts of this paper were provided by M.Cake, K. Johnson, and D. Pethick. Financial sup-port was provided by the Australian ResearchCouncil and the Murdoch University Research In-frastructure Fund.

LITERATURE CITEDBartholomew, G.A. (1982) Energy metabolism. In: Animal

Physiology: Principles and Adaptations, 4th ed. M.S. Gor-don, ed. MacMillan Press, New York, pp. 46–92.

Beamish, F.W.H., and P.S. Mookherjii (1964) Respiration offishes with special emphasis on standard oxygen consump-tion. I. Influence of weight and temperature on respirationof goldfish, Carassius auratus. Can. J. Zool., 42:161–175.

Beamish, F.W.H., I.C. Potter, and E. Thomas (1979) Proxi-mate composition of the adult anadromous sea lamprey,Petromyzon marinus, in relation to feeding, migration andreproduction. J. Anim. Ecol., 48:1–19.

Berg, T., and J.B. Steen (1965) Physiological mechanisms foraerial respiration in the eel. Comp. Biochem. Physiol.,15:469–484.

Bird, D.J., and I.C. Potter (1983) Proximate composition atvarious stages of adult life in the Southern Hemisphere lam-prey, Geotria australis Gray. Comp. Biochem. Physiol.,74A:623–633.

Bridges, C.R. (1988) Respiration adaptations in intertidal fish.Am. Zool., 28:79–96.

Burggren, W., K. Johansen, and B. McMahon (1985) Respi-ration in phyletically ancient fishes. In: Evolutionary Biol-ogy of Primitive Fishes, Vol. 3. R.E. Foreman, A. Gorbman,J.M. Dodd, and R. Olsson, eds. Plenum Press, New York,pp. 217–252.

Claridge, P.N., I.C. Potter, and G.M. Hughes (1973) Circa-dian rhythms of activity, ventilatory frequency and heartrate in the adult river lamprey, Lampetra fluviatilis. J. Zool.Lond., 171:239–250.

Claridge, P.N., and I.C. Potter (1975) Oxygen consump-

tion, ventilatory frequency and heart rate of lampreys(Lampetra fluviatilis) during their spawning run. J. Exp.Biol., 63:193–206.

Feder, M.E., and W.W. Burggren (1985) Cutaneous gas ex-change in vertebrates: design, patterns, control and impli-cations. Biol. Rev., 60:1–45.

Gordon, M.S. (1995) Functional evidence from living ver-tebrates. In: Invasions of the Land. M.S. Gordon andE.C. Olsen, eds. Columbia University Press, New York,pp. 216–250.

Graham, J.B. (1973) Terrestrial life of the amphibious fishMnierpes macrocephalus. Mar. Biol., 23:83–91.

Hardisty, M.W. (1982) Lampreys and hagfishes: analysis ofcyclostome relationships. In: The Biology of Lampreys, Vol.4B. M.W. Hardisty and I.C. Potter, eds. Academic Press,London, pp. 165–259.

Kirsch, R., and G. Nonnotte (1977) Cutaneous respiration inthree freshwater teleosts. Respir. Physiol., 29:339–354.

Korolewa, N.W. (1964) [Water respiration of lamprey and itssurvival in a moist atmosphere.]. Izv. Vses. Nauchno-issled.Inst. Ozern. Rechn. Ryb. Khoz., 58:186–190 [in Russian].

Lewis, S.V., and I.C. Potter (1976) Gill morphometrics of thelampreys Lampetra fluviatilis (L.) and Lampetra planeri(Bloch). Acta Zool. Stockh., 57:103–112.

Lewis, S.V., and I.C. Potter (1982) A light and electron mi-croscope study of the gills of larval lampreys (Geotria aus-tralis) with particular reference to the water-blood pathway.J. Zool. Lond., 198:157–176.

Macey, D.J., L.M. Clarke, and I.C. Potter (1991) Basal oxygenconsumption, ventilatory frequency, and heart rate duringthe protracted spawning run of the Southern Hemispherelamprey Geotria australis. J. Comp. Physiol., 161:525–531.

Martin, K.L.M. (1993) Aerial release of CO2 and respiratoryexchange ratio in intertidal fishes out of water. Environ.Biol. Fish., 37:189–196.

Martin, K.L.M. (1995) Time and tide wait for no fish: inter-tidal fishes out of water. Environ. Biol. Fish., 44:165–181.

Martin, K.L.M., T.M. Berra, and G.R. Allen (1993) Cutane-ous aerial respiration during forced emergence in the Aus-tralian salamanderfish, Lepidogalaxias salamandroides.Copeia, 1993:875–879.

Moore, J.W., and I.C. Potter (1976) Aspects of feeding andlipid deposition and utilization in the lampreys, Lampetrafluviatilis (L.) and Lampetra planeri (Bloch). J. Anim. Ecol.,45:699–712.

Nonnotte, G (1981) Cutaneous respiration in six freshwaterteleosts. Comp. Biochem. Physiol., 70A:541–543.

Pelster, B., C.R. Bridges, and M.K. Grieshaber (1988) Physi-ological adaptations of the intertidal rockpool teleostBlennius pholis L., to aerial exposure. Respir. Physiol.,71:355–374.

Potter, I.C. (1980) Ecology of larval and metamorphosing lam-preys. Can. J. Fish. Aquat. Sci., 37:1641–1657.

Potter, I.C., and R.W. Hilliard (1987) A proposal for the func-tional and phylogenetic significance of differences in thedentition of lampreys (Agnatha: Petromyzontiformes). J.Zool. Lond., 212:713–737.

Potter, I.C., R.W. Hilliard, D.J. Bird, and D.J. Macey (1983)Quantitative data on morphology and organ weights dur-ing the protracted spawning-run period of the SouthernHemisphere lamprey Geotria australis. J. Zool. Lond.,200:1–20.

Potter, I.C., D.J. Macey, A.R. Roberts, and P.C. Withers (1996a)Oxygen consumption by ammocoetes of the lamprey Geotriaaustralis in air. J. Comp. Physiol., 166B:331–336.

298 I.C. POTTER ET AL.

Potter, I.C., D.J. Macey, and A.R. Roberts (1996b) Oxygenconsumption by adults of the southern hemisphere lampreyGeotria australis in air. J. Exp. Zool., 276:254–261.

Potter, I.C., U. Welsch, G.M. Wright, Y. Honma, and A. Chiba(1995) Light and electron microscope studies of the dermalcapillaries in three species of hagfishes and three speciesof lampreys. J. Zool. Lond., 235:677–688.

Randall, D.J. (1972) Respiration. In: The Biology of Lampreys,Vol. 2. M.W. Hardisty and I.C. Potter, eds. Academic Press,London, pp. 287–306.

Randall, D.J., W.W. Burggren, A.P. Farrell, and M.S. Haswell(1981) The evolution of air breathing vertebrates. CambridgeUniversity Press, Cambridge.

Schmidt-Nielsen, K. (1990) Animal Physiology. CambridgeUniversity Press, Cambridge.

Steeger, H.-U., and C.R. Bridges (1995) A method for long-term measurement of respiration in intertidal fishes dur-ing simulated intertidal conditions. J. Fish Biol., 47:308–320.

Tamura, S.O., H. Morii, and M. Yuzuriha (1976) Respirationof the amphibious fishes, Periophthalmus cantonensis andBoleophthalmus chinensis in water and on land. J. Exp.Biol., 65:97–107.

Teal, J.M., and F.G. Carey (1967) Skin respiration and oxy-gen debt in the mudskipper Periopthalmus sobrinus. Copeia,1967:677–679.

Tufts, B.L. (1991) Acid-base regulation and blood gastransport following exhaustive exercise in an agnathan,the sea lamprey Petromyzon marinus. J. Exp. Biol.,159:371–385.

Yokoya, S., and O.S. Tamura (1992) Fine structure of the skinof the amphibious fishes, Boleophthalmus pectinirostris andPeriophthalmus cantonensis, with special reference to thelocation of blood vessels. J. Morphol., 214:287–297.

Youson, J.H., and P.A. Freeman (1976) Morphology of the gillsof larval and parasitic adult sea lamprey Petromyzonmarinus L. J. Morphol., 149:73–104.