5

R app. P.-v. Réun. Cons. int. Explor. M er, 174: 5-6. 1979.

P R E F A C E

F. T h u r o w

Institut für Küsten- und Binnenfischerei der Bundesforschungsanstalt für Fischerei, Wischhofstrasse 1, D-2300 Kiel, Bundesrepublik Deutschland

Investigations on eel have only recently become a subject of wide international cooperation, which began when the European Inland Fisheries Advisory Com­mission started to promote joint efforts. An ad hoc working group on eel fishing gear and techniques was established, and subsequently a workshop on com­parative ageing was held in Montpellier, France. A further step was taken when EIFAC approached the International Council for the Exploration of the Sea for assistance in defining fields and ways of cooperating. As a result the Joint Symposium on Eel Research and Management was organized and held 9-11 June 1976 in Helsinki. Arrangements were planned by a steering committee consisting of J . Boëtius, J . Dahl, C. J. M cGrath (Rapporteur), F. Thurow, K. Tiews (Con­vener), and R. Welcomme. C. J . McGrath (EIFAC) and F. Thurow (ICES) were appointed chairmen of the symposium. Five consecutive panels were estab­lished and led as follows:

(1) Appraisal of the present status of eelfisheries I. Boëtius

(2) Measures for the improvement and main­tenance of eel fisheries I. Boëtius

(3) Age and growth under natural and artificial conditions C. L. Deelder

(4) Migration and reproductive phase F.-W. Tesch(5) Conclusions and recommendations F. Thurow

Papers submitted and other relevant information were presented by the panel leaders and discussed by the participants. This led to the conclusion that an assessment of the state of exploitation and of the effect of elver stocking was urgently needed. The Baltic, the North Sea, the Atlantic between the English Channel and Gibraltar, and the Mediterranean were tenta­tively identified as management units, with the areas extending seaward as well as inland. I t was recom­mended that EIFAC and ICES working groups co­operate to improve ageing by comparative reading of

otoliths of known age and by analysis of otolith struc­tural development. Further, the organization of an international expedition to the supposed spawning areas of the European eel was finally recommended. A full account of the discussions at the symposium has been published in EIFAC Tech. Pap. No. 28.

Fifty-four reports were made available to the sym­posium. This volume contains 22 articles based on 25 symposium papers. They are arranged in approx­imately the same sequence as the panels.

Many referees have contributed to the preparation of this volume. They have unselfishly rendered their assistance and used much of their time to aid this work.

My personal thanks go to the Technical Editor, Mrs J . Rosenmeier. Much of what is achieved in editing this volume is due to her efficient work.

The following reports, partly published elsewhere, were also prepared for the symposium:

Anon. 1976. First report of the W orking G roup on stocks o f the European eel. ICES CM 1976/M: 2, 33pp . (mimeo).

Bieniarz, K ., Epier, P., Cedrowski, A., and Sokolowska, M . 1976. Eel culture in artificial conditions. Rocz. N auk rol., H-98-4.

Boëtius, I., and Boëtius, J . Fecundity of the European eel. Dana. (In press).

Boëtius, I., and Boëtius, J . Estimate o f an energy budget for m igration and spawning of female European eels. Dana. (In press).

Ciepielewski, W. 1976. The size, sex, and age of seaward migrating eel from two M asurian lakes. Rocz. Nauk rol., H-97-2.

Deelder, C. L. 1976. Remarks on the age determ ination of eels with length back calculations. Aquaculture, 9 : 373-379.

Dembinski, W ., and Swierzowski, A. Selectivity o f eel pound-nets and the size structure o f eel populations m igrating downstream. (To be publ. in Rocz. Nauk rol.)

Dembinski, W ., and Swierzowski, A. Effectiveness o f electric eel fishing in Poland. (To be publ. in Rocz. N auk rol.)

Dembinski, W ., M ayer, I., and Swierzowski, A. Catches and selectivity o f an electrified eel seine net. (To be publ. in Rocz. Nauk rol.)

D eufel,J., and Strubelt, T . 1976. Running o f eel stocks in the Lake of Constance. Österr. Fisch., 29 (11/12): 189-195.

Descamps, B., Foulquier, L., and G rauby, A. E tude comparée de

6 F. T h u row : Preface

la croissance des anguilles en fonction de la tem pérature dans deux bassins en circuit ouvert.

H errm ann, G. O n the eel yields of inland fishery in the Federal Republic o f Germany.

Koops, H ., and Kuhlm ann, H . Prelim inary note on the growth of the European eel in a brackish therm al effluent.

Lam arque, P. 1976a. Types de courant électrique à utiliser pour la capture optim ale des anguilles. Piscic. Fr., 47: 30-37.

Lam arque, P. 1976b. A ppareil pour la mesure et la pesée d ’anguilles anesthesiées électriquem ent. Piscic. Fr., 47: 38-39.

Leopold, M . State o f eel m anagem ent in Poland.Leopold, M . Stocking as a m ain factor determ ining the level of

eel catches in Poland.Leopold, M . Basic problems of eel exploitation.Leopold, M . The effect o f trophic and biological conditions on eel

production and management.Leopold, M . Efficiency and prospectives o f eel m anagement.M cG rath, C. J . R eport o f the EIFA C W orkshop on age deter­

m ination of eels, M ontpellier, M ay 1975.M cG rath, C .J . R eport o f the second m eeting of the EIFA C ad

hoc W orking G roup on eel fishing gear and techniques, Dublin, M arch 1974.

Passakas, T . 1976. Further investigations on the chromosomes of Anguilla anguilla. Folia biol., 24 (2) : 239-244.

Peters, G. 1977. The papillomatosis (cauliflower disease) o f the European eel (Anguilla anguilla) : fluctuations in the rate of incidence in the Elbe and their causes. Arch. FischWiss., 27 (3): 251-263.

Saint Paul, U . 1977. Young eels in N orth Sea river estuaries caught for stocking purposes. Arch. FischWiss., 28 (2/3): 123-135.

Serene, P. M arché de l ’anguille en Europe. E tude d ’approche.Stott, B. O n the present state o f the eel resources in England

and Wales.Svärdsson, G. 1976. T he decline o f the Baltic eel population.

Inst. Freshw. Res. D rottningholm , 55: 136-144.Swierzowski, A. 1975a. General analysis o f eel catches in rivers

and lakes o f the drainage basin o f N arew river. Rocz. Nauk rol., H-96-4.

Swierzowski, A. 1975b. R hythm and intensity o f silver eel catches in the drainage basin o f N arew river. Rocz. N auk rol., H-96-4.

Swierzowski, A. The effect o f a smooth rectified electric current on the behaviour and metabolism of eel. (To be publ. in Rocz. Nauk rol.)

Veen, T . van, Frem berg, M ., H artw ig, H . G., and M üller, K . 1976. Photoreception and circadian rhythm in the eel. J . Comp. Physiol., I l l : 209-219.

144

R app. P.-v. Réun. Cons. int. Explor. M er, 174: 144-149. 1979.

T H E E F F E C T S O F P E N T A C H L O R O P H E N O L O N S W I M M I N G P E R F O R M A N C E A N D O X Y G E N C O N S U M P T I O N I N T H E A M E R I C A N E E L (.A N G U I L L A R O S T R A T A )

B. H o l m b e r g 1 and R. L. S a u n d e r s 2

Environm ent Canada, Fisheries and M arine Service, Biological Station,St Andrews, New Brunswick, Canada

Yellow and silver (migrating) eels were forced to swim a t a tem perature o f 15 °C in a tunnel respirometer for one hour a t each of a series o f progressively greater speeds (35, 45, 55, and 65 cm/s) with 30 m inutes’ rest before each increase. There was no significant difference between the rates of 0 2 consumption of yellow and silver eels and the energy cost of transportation a t the various swimming speeds. However, glucose and lactate levels increased above resting values in only the yellow eels. This indicates that silver eels are better adap ted for swimming.

Yellow (non-migrating) eels were exposed to pentachlorophenol (PCP) a t a concentration of 0 1 ppm in fresh w ater and subsequently for four days in clean w ater before being exercised in a respirometer. After one hour a t a low swimming speed the w ater velocity was increased to 35 cm/s and m aintained for five hours. A control group was similarly exercised bu t w ithout prior treatm ent with PCP. Standard (resting) metabolism was measured in similar PC P-treated and control groups. PC P treatm ent increased the active and standard rates of 0 2 consumption above rates o f controls. After correction for the higher standard metabolism the exercise was equally costly for control and poisoned eels. There was no difference in glucose and lactate levels between control and PC P-treated yellow eels.

IN T R O D U C T IO N

Pentachlorophenol (PCP) has been used extensively as a fungicide, bactericide, herbicide, and insecticide. I t is a powerful uncoupling agent of oxidative phospho­rylation. Because of its widespread use in wood pre­servation and as an insecticide, PCP finds its way into the aquatic ecosystems. The objective of the research reported here was to find out to what extent PCP affects the oxygen consumption and swimming per­formance of the American eel. In addition, we deter­mined the standard and active rates of oxygen con­sumption for eels in both the yellow or stream-resident stage and the silver or migratory stage.

Previous studies with the European eel (Anguilla anguilla L.) showed that exposure to PCP resulted in a hyper-metabolic condition and accelerated con­sumption of energy reserves (Holmberg et al., 1972). These studies also suggested a disruption of liver function. O f special importance considering the long residence of eels in fresh water and the possibility of repeated doses of the metabolic poison, was the further conclusion that effects lasted more than two months during recovery in clean water.

1 Present address: National Board of Fisheries, Box 2566, S-403 17 Gothenburg, Sweden.

2 Present address: N orth Am erican Salmon Research Center, St Andrews, New Brunswick, C anada.

The eel is of particular interest because of its diverse behaviour, first as a larva drifting with ocean currents before actively swimming upstream, followed by long residence in a river and finally an active migration from the river to its supposed spawning place in the Sargasso Sea. In view of the metabolic effects of PCP on eels shown by Holmberg et al. (1972), it is of importance to compare resident and migratory eels in respect to oxygen consumption and swimming performance because of the likely changing metabolic and activity demands between resident and migratory eels.

M A TER IA LS

The fish used in the experiments was the American eel (Anguilla rostrata). Yellow eels were trapped in a tidal pond outside St Andrews, N.B., in July/August 1971 and were then kept in tanks with running fresh water at 15°C. The eels were stored a t least a week before beginning the experiments and were not fed. Silver eels were trapped in streams outside St Andrews, N.B., during September when migrating downstream. These eels were still feeding in the streams. They were stored in the same way as the yellow eels. The eels were black with silvery bellies but turned lighter in the holding tanks. Sex was determined after the

T he effects o f pentachlorophenol on swim ming perform ance and oxygen consum ption in the A m erican eel 145

experiments and only female eels were used. The average gonado-somatic index (GSI = (gonad weight x 100)/body weight) for the silver eels was 3-03 and 0-65 for the yellow eels.

M E T H O D S

STANDARD RATE OF OXYGEN CONSUMPTION

Standard rates of oxygen consumption were deter­mined from September to November for individual eels by measuring simultaneously the routine rate of oxygen consumption and spontaneous activity as described by Beamish and Mookerjii (1964). Our respirometer had a volume of 22 1 and was largely patterned after that used by Beamish and Mookerjii. The activity detector was a standard thermoregulator (M athur and Shrivastava, 1970) with its bulb im­mersed, together with a 5-V DC heater across a 10-ohm resistance, in a closed mercury reservoir. The heater was set to maintain the temperature in the mercury reservoir 2 °C higher than that in the water in the respirometer. Movements by the eel produced water currents that cooled the bulb of the activity meter and caused the heater to go on. This increased the time that the heater needed to be in circuit to maintain the 2° differential. This increase, measured by a resettable cycling timer, was used as a measure of the activity of the fish. An activity baseline was determined a t the beginning and end of each experi­ment by measuring the time the heater was in circuit with no fish in the respirometer.

For measurements of oxygen consumption, eels were removed from the holding tank in late afternoon, anaesthetized in MS-222, weighed and measured, and then placed one in each of three respirometers with flowing water of the holding temperature. Light was excluded from the respirometers to reduce visual stimulation of the fish.

Oxygen concentrations in the water were measured at the beginning and end of periods of respirometer closure. The eels were allowed to reduce the oxygen concentration in the closed respirometer to between 15 and 50% of the air saturation value, the time required to do this ranging from 4 to 6 hours. Owing to the low rate of oxygen consumption of eels in comparison with Atlantic salmon parr (Withey and Saunders, 1973), the determinations of oxygen con­sumption were made in 3 to 4 stages as the ambient 0 2 level fell during the 4 to 6 hour period of respiro­meter closure. At the end of a run, the respirometers were flushed with air-saturated water to restore the 0 2 level. Three to five 0 2 determinations were made during each of 2 or 3 days to gather the data for each fish. The eels were removed after the final measure­ment and again weighed.

In determining the standard rate for each fish, by extrapolation of the line of best fit to zero activity (Beamish and Mookerjii, 1964), little extrapolation was required because, with eels, most activity values were close to zero. Evidently, eels remained very inactive in the darkened respirometers. Perhaps the inactivity was owing to the determinations being made during daylight hours. No attempts were made to measure changes in activity and resulting metabolism owing to diurnal or lunar cycles (Lowe, 1952; Boëtius, 1967). When the activity values were all close to zero, no line of best fit could be drawn and standard rates were taken as the mean of the low values.

The narrow weight range of our yellow eels inval­idated comparison of rates of oxygen consumption between groups by the usual method of plotting the log rate in mg 0 2/h against log fish weight and com­paring slopes and intercepts (Winberg, 1961 ; Saunders, 1963). Finding no significant difference (by t-test) between mean weights of treated and untreated yellow eels, we analysed for differences in rates of oxygen consumption between groups, using the t-test. How­ever, the mean weight of silver eels was significantly higher than that of yellow eels, and this necessitated using the graphic analysis referred to above.

OXYGEN CONSUMPTION OF SWIMMING EELS

The experiments were performed in a modified version of the Blazka tunnel respirometer (Blazka et al., 1960; Smith and Newcomb, 1970) made of Perspex and with a volume of 41-2 liters. The swim­ming tunnel was 108 cm long and 12 cm in diameter. The eel was forced to swim in the inner tunnel against a water current created by a propeller. The current velocity was estimated from a calibration graph. A grid carrying an electrical charge was situated behind the fish to prevent it from resting during the experi­ment. Another grid was also placed in front of the fish. The respirometer was shielded from light by a black plastic sheet during the experiments. The eel was left overnight in the respirometer with running water before the start of the experiment the next day.

To measure the amount of oxygen consumed by the swimming eel, the water supply was cut off during the run. The oxygen consumption was calculated from the oxygen concentrations a t the beginning and at the end of the experimental period (ca. 1 hour). During the run the oxygen concentration dropped not more than about 10%. Between two runs, the respirometer was flushed with aerated water.

Experiments at increasing swimming speedsIn a series of experiments, eight silver and eight

yellow eels were used. The mean length of the silver

10

146 B. H olm berg and R . L. Saunders

eels was 54 cm, ranging from 48 to 57 cm. The mean weight was 262 g, ranging from 189 to 316 g. For the yellow eels the mean length was 53 cm, with the range 49-58 cm, and the mean weight was 224 g, with the range 176-336 g. The oxygen consumption of each eel was measured during 1 hour at swimming speeds of 35, 45, 55, and 65 cm/s. Between each speed the eel was rested 30 min and the respirometer was flushed with aerated water. After the run the eel was taken out for analysis of blood glucose, lactate and hematocrit.

Tests at continuous swimming and the effects o f treatment with pentachlorophenol

In these experiments eight yellow eels were treated with pentachlorophenol (PCP). Each eel was held in a tank (60 1) containing an aerated water solution of 0-1 ppm PCP. The exposure time was 4 days and the solution was renewed after 2 days. For PCP residues in the tissues see Holmberg et al. (1972). They found after 4 days of exposure at 12 °C in a solution of 0T ppm PCP, a pesticide content in liver: 10 ppm, blood : IT ppm, and muscle : 1 -0 ppm. After 4 days of recovery the pesticide content was 1-5 ppm, 0-7 ppm, and 0-5 ppm respectively. Before beginning the ex­periments in the respirometer, each eel was incubated in clean running water for another 4 days. Control eels were treated the same way but without PCP. For each experiment, a pair of eels of about the same size was chosen as test and control animals. The mean length of PCP-treated and control eels was 51 cm. The mean weights of PCP-treated and control fish w e re 202 a n d 212 g re sp ec tiv e ly .

In the Blazka respirometer the eels swam at a slow speed the first hour. Then the swimming velocity was increased to 35 cm/s and maintained for 5 hours. The oxygen consumption was calculated for the first hour at slow speed and the first, third, and fifth hours at the velocity of 35 cm/s. After the run the eels were taken out for blood analysis.

Oxygen analyses were made with a W PRL drop­ping mercury electrode (Southern Analytical, Surrey, U .K .). All the experiments were done a t a water temperature of 15 ± 0-2 °C.

TEST SUBSTANCE AND BLOOD ANALYSIS

Sodium pentachlorophenol, technical grade (Fluka AG), was dissolved in distilled water to a concentration of 250 ppm. This stock solution was used to obtain the final concentration of 0-1 ppm in the tanks for treatment of eels.

After the run the respirometer was emptied and the eel was taken out and lightly anaesthesized in a water solution of MS-222. The eel was weighed before and

after the run. About 20 to 30 min after the swimming, blood was taken from caudal vessels with a heparinized syringe. Portions of whole blood were taken for hematocrit, glucose, and lactate determinations. Glucose and lactate were analysed enzymatically and hematocrit was determined in heparinized capillary tubes which were centrifuged (Holmberg et al., 1972). A control group of unexercised yellow and silver eels was also analysed for hematocrit, glucose, and lactate.

RE SU L T S AND D ISC U SSIO N

STANDARD RATE OF OXYGEN CONSUMPTION

Although yellow eels showed a consistent trend of higher metabolism than silver eels (Table 57), the difference was not statistically significant. The silver eels were significantly larger (P < 0-01) than the yellow eels. Considering that small individuals have a higher rate of oxygen consumption per unit weight than large fish of the same species (Winberg, 1961; Saunders, 1963), the higher rate of oxygen consump­tion of the yellow eels was apparently owing to their smaller size rather than to metabolic differences between yellow and silver eels. The lack of difference between the two phases was also seen in their active rates of oxygen consumption (see below).

Treatm ent with PCP resulted in a statistically significantly higher standard rate of oxygen con­sumption in yellow eels than in untreated controls (PcO-Ol) (Table 57). The difference between mean weights of PCP-treated and untreated yellow eels was n o t s ta tis t ic a lly s ign ifican t.

Only three silver eels were available for PCP treatment. They had standard rates of oxygen con­sumption nearly twice those of untreated silver eels.

O ur values for standard rate of oxygen consumption in untreated controls are in good agreement, when corrections are made for differences in temperature, with those of Egusa (1958) who measured resting rates of the Japanese eel {Anguilla japonica) of various sizes at 25 °C. (Body weight 200 g : 51 cc/kg/h).

Table 57. Standard metabolism of silver and yellow eels and the effect of PCP treatment of yellow eels. Means ± SE

Num ber

(g)

M eanweight

(g)

0 2 consumption (mg 0 2/kg/h)

Silver........................... 12 315 21 ± 2Y ellow ......................... 12 214 28 ± 1PC P-treated yellow . 12 197 46 ± 3

T h e effects of pentachlorophenol on swimming perform ance and oxygen consum ption in the A m erican eel 147

Table 58. 0 2 consumption of yellow and silver eels at various swimming speeds, n = 8. Means ± SE

M ean M ean 0 2 consumption (mg/kg/h)length weight a t various swimming speeds(cm) (g) 35 cm/s 45 cm/s 55 cm/s 65 cm/s

Yellow. 53 224 152 ± 12 195 ± 12 248 ± 16 (249)S ilv e r.. 54 262 123 ± 10 161 ± 9 215 ± 9 (265)

P - - i > > 0 1 0 P < 0 0 5 i ><0-10

EXPERIMENTS AT INCREASING SWIMMING SPEEDS

The oxygen consumption of yellow and silver eels was estimated a t swimming speeds 35, 45, 55 and 65 cm/s (Table 58). At the swimming speed 65 cm/s four of the yellow eels and three of the silver eels failed to swim for one hour.

Only at 45 cm/s was there a significantly higher ox­ygen consumption of yellow eels. In most fish the slope describing the relation between log mg 0 2/h and log weight is about 0-8 (Winberg, 1961). If the oxygen consumption in these series of experiments were cor­rected for the effect of weight, the difference between silver and yellow eels would be even less than shown in Table 58.

I f the metabolic data from swimming yellow and silver eels are plotted against swimming speed (Fig. 90), it is possible to derive standard rates of oxygen consumption by extrapolating to 0 swimming speed (Smit et al., 1971). The values thus derived for yellow and silver eels, 66 and 48 mg/kg/h respectively, are both higher than the standard rates obtained for eels in the Beamish respirometers. In this case, the re­spective mean weights of yellow and silver eels were similar for the two methods of deriving standard rate and, therefore, weight effect can be ruled out as the causative factor. As noted by Brett (1964), Smit et al.(1971), Smit (1965), and K utty and Saunders (1973), fishes in a respirometer swim erratically when they are not hard pressed to swim against a high current velocity. The result is that a t slow swimming speeds they often expend more energy through their erratic swimming and consume more oxygen than a t slightly higher speeds. O ur determinations of standard rate were made for eels in darkened chambers in which the fish were undisturbed for long periods. This probably accounted for the low activity levels.

I t is of interest that Atlantic salmon (Salmo salar), for which standard rates were determined at 15°C using the same Beamish respirometers, had standard rates from 3 to 4 times higher than eels (Saunders and Henderson, unpublished data). Both species commonly inhabit the same streams and live in similar habitats. Whereas Atlantic salmon live in open water and spend most of their time swimming against the current, eels

10 0 0

- o

s i l v e r m e a n w t 2 6 2 g

Ö ye l low - m e a n w t = 2 1 4 q

swimming speed cm /s

Figure 90. S tandard rates of oxygen consumption by extra­polating to 0 swimming speed and da ta from the respirometer.

usually hide among the gravel. These differences in behaviour are suggested as contributing factors to the great differences in metabolic rate between species living in the same habitat.

The oxygen consumption of a fish will be an in­correct measurement of the energetic cost of trans­portation if the fish is repaying an oxygen debt during its activity. This may be indicated by an increased level of lactate in the blood. The eels in the experiment were analysed for glucose, lactate, and hematocrit after the exercise. I t can be seen from Table 59A, that the concentrations in the blood of glucose and lactate were doubled in the yellow eels. For the silver eels the concentrations were almost the same after the exercise compared with unexercised eels (Table 59B).

One conclusion from our experiments is that the silver eel is better adapted for physical exercise than the yellow eel. Boström and Johansson (1972) reported for European eel (A. anguilla) higher activity values of the oxidative enzymes in both red and white muscle of the silver eel compared with the yellow eel. The mitochondria had a greater oxidative capacity in the silver eel. The amount of red muscle also increased in the silver eel stage.

To convert the amount of oxygen consumed to the number of calories of energy utilized, the relative amounts of fat, carbohydrate, and protein being me-

10*

148 B. H olm berg and R . L. Saunders

Table 59 A and B. Glucose, lactate, and hematocrit in blood of yellow and silver eels. Means ± SE

A. After swimming a t various speeds. Eels from T able 58.

M ean M ean T •»r -i i , . Glucose Lactate N um ber length weight (mg/10Qml) (mg/100ml)

H em atocrit

(%)

Yellow 8 53 224 152 ± 21 54 ± 9 37 ± 1Silver. 8 54 262 81 ± 12 24 ± 5 37 ± 1

P . . . . P < 0 05 P < 0-05 P > 0 - 1 0

B. Unexercised.

M ean M ean Glucose Lactate H em atocritN um ber length weight (mg/100ml) (mg/100ml) (%)

(cm) (g)

Yellow 8 50 182 75 ± 11 16 ± 1 35 ± 1Silver. 6 57 309 79 ± 16 20 ± 1 38 ± 2

P . . . . - - - P > 0-10 P < 0-05 P > 0 - 1 0

tabolized must be known. For our experiments this relation is not known. I t cannot be excluded that the silver eel utilizes a higher fraction of fat compared with the yellow eel. Lewander et al. (1974) found for the European eel a higher content of blood lipids in the silver stage and concluded that this might re­flect increased use of fat as an energy source.

From our data, K. Schmidt-Nielsen (1972) calcu­lated that the cost of transportation for the eel was 0-329-0-417 cal/g/km. He concluded that the energy cost of swimming for eels is similar to that for other fishes despite the different body form and way of swimming.

TH E EFFECT OF PCP TREATMENT

The PCP-treated eels had a higher oxygen con­sumption than the untreated ones when swimming at 35 cm/s for 5 hours (Table 60). When the oxygen consumption was corrected for the difference in standard metabolism, there was no significant dif­ference between the two groups at “ slow speed” and the first and third hours of swimming (Table 57). This finding is in agreement with that of Crandall and Goodnight (1962), who found an elevated standard rate bu t no change in active rate of oxygen consump­tion of PCP-treated guppies. During the fifth hour there was a significant drop in oxygen consumption for the untreated eels. Even after correction for the difference in standard metabolism, there was a signi­ficantly higher oxygen consumption for the PCP- treated eels during the fifth hour of swimming. The higher oxygen consumption may indicate a stress situation for the PCP-treated eels even after 5 hours of swimming. I t was also observed that PCP-treated eels were very sensitive to external disturbances.

Table 60. 0 2 consumption (mg/kg/h) of yellow eels after PCP treatment during 1 h “slow” speed and 5 h continuous swimming at 35 cm/s. n = 8. Means ± SE

M ean r 0 2 consumption m g/kg/h Aweight “ Slow” ^ :Speed: 35 cm /s-------- ^

(g) speed First h T h ird h Fifth h

PCP-treated 202 91 ± 9 159 ± 7 165 ± 9 165 ± 7

Controls 212 58 ± 9 130 ± 19 128 ± 10 102 ± 8

P P < 0-05 P < 0 1 0 P < 0 05 P < 001

PCP has been reported as a strong uncoupling agent of oxidative phosphorylation (for review see Bevenue and Beckman, 1967).

Kreuger et al. (1968) found that PCP increased the caloric loss during starvation by 125%, but exercise was equally costly in control and poisoned cichlids. These results confirm our findings for the yellow eels.

Holmberg et al. (1972) found an increase in blood glucose in resting European eels following exposure to PCP. This indicated a hypermetabolic state. In our experiments there was no increase in blood glucose of PCP-treated eels following exercise (Table 61). I t has been demonstrated for some fishes that oxygen con­sumption during sustained swimming a t moderate and high speeds does not meet the metabolic demand and that an oxygen debt must be paid during a period of rest (Driedzic and Hochachka, 1976). The im­mediate source of energy for strenuous exercise is glycogen stored in the swimming muscles. O ur glucose data, in comparison with that of Holmberg et al.(1972), and our observations of increased responses to external stimuli suggest that sublethal doses of PCP increase the excitability of the fish under resting con­ditions, with consequent elevated glucose metabolism and oxygen consumption, bu t that the metabolism associated with strenuous activity is little affected. In support of this suggestion that PCP affects the pathway for resting metabolism but not that for active swimming, Webb and Brett (1973) found that, al­though PCP at concentrations of ca. 1-8 ppb reduced

Table 61. Glucose, lactate, and hematocrit in blood of PCP-treated yellow eels after swimming at 35 cm/s. n = 8. Means ± SE

Glucose (m g/100 ml)

Lactate (m g/100 ml)

Hem atocrit(%)

P C P -tre a te d ......... 75 ± 11 14 ± 2 29 ± 1C o n tro ls ................ 88 ± 9 19 ± 3 32 ± 1

P ............................. P > 0-10 P > 0 1 0 P > 0 1 0

T he effects of pentachlorophenol on swimming perform ance and oxygen consum ption in the A m erican eel 149

growth rate and food conversion efficiency of sockeyesalmon (Oncorhynchus nerka), swimming performancewas not reduced.

R EFER EN C ES

Beamish, F. W. H ., and Mookerjii, P. S. 1964. Respiration of fishes w ith special emphasis on standard oxygen consumption. I. Influence of weight and tem perature on respiration of goldfish, Carassius auratus L. Can. J . Zool., 42: 161-175.

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