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Respiration of juvenile Pollock, Theragra chalcogramma (Pallas), relative to body size and temperature
f. Exp. Mar. B&I. Ewl., 1986, Vol. 97, pp. 287-293
287
Elsevier
JEM 670
RESPIRATION OF JUVENILE POLLOCK, THERAGRA
CHALCOGRAMMA
(Pallas), RELATIVE TO BODY SIZE AND TEMPERATURE’
A.J. PAUL University of Alaska, Institute of Marine Science, Seward Marine Center, P.O. Box 730, Seward, Alaska 99664, U.S.A.
(Received 27 November 1985; revision received 12 February 1986; accepted 14 February 1986) Abstract: Measurements of oxygen consumption by starved juvenile pollock, Theragra chalcogramma (Pallas), relative to body size and water temperature were determined. Oxygen consumption rates for 6-300 g pollock were described by the equation: log ~10,. h- ’ = 12.78 + 0.755 (logg wet wt) at 5.5 “C. The temperature range normally experienced by this species in Aiaska is 1-12 “C. Weight specific oxygen consumption (yOl) for 40-9Og fish exhibited a Iinear increase between 1 and 7.5_“C described by the equation: PO, (pl*g-‘.h-‘)= 12.617 + 7.961 (temp. “C). Values for specific VO, were similar between 7.5 and 12°C. The estimate for Q,, (1-12 “C) was 2.5, similar to other cold-water fish. The daily energy expenditure due to respiration for unfed fish is calculated and compared to other existing estimates. Key words: oxygen consumption; energy requirements; Theragra cha~~~~~mrna
INTRODUCTION
The pollock, Therugra c~~ZC~~~~~~, is an important commercial species and forage fish in Alaskan waters. In the southeastern Bering Sea it constitutes 20 to 50% of the total fish community biomass (Pereyra et al., 1976). The total commercial catch averaged 4.4 million metric tons a year during the 1970’s. Pollock are major food items in the diets of marine mammals, birds and several fish species. Currently, yield models are being constructed to provide harvest guidelines for pollock (Laevastu & Larkins, 198 1). These models and ecological studies of Alaskan marine systems require estimates of pollock energy requirements. Recent studies have provided some energetic estimates (Fukuchi, 1976; Paul, 1983; Yoshida & Sakurai, 1984; Smith et al., 1986; Harris et aZ., in press), but none of these experiments was carried out utilizing the entire range of temperatures that this species encounters in Alaska. Furthermore, in each of the studies only a limited size range of fish were used in experiments. Thus, with the existing ~fo~ation, it is difficult to estimate energetic needs of pollock relative to their body size and the water temperature. The objective of this study was to provide additional information on pollock metabolic energy needs by measuring specific oxygen consumption rates (PO,) ’ Contribution Number 609 from the institute of Marine Science, University of Alaska. 0022-0981/86/$03.50 0 1986 Elsevier Science Publishers B.V. (Biomedical Division)
A. J. PAUL
288
of juvenile pollock as a function of fish size (6 to 300 g) within the range of water temperature they normally experience. In the southeastern Bering Sea, juvenile pollock primarily inhabit water between 0 and 7 “C, with a range of - 1.2 to 11.2 “C (Chen, 1983).
MATERIALS
AND
METHODS
Weight related oxygen consumption was measured for 15 fish, 6 to 300 g, at 5 to 6 ‘C. Fish under 135 g were held in a 23.5-l respiration chamber and larger fish in 208-l chambers. Fish were kept at test temperatures for at least 2 wk, not fed for 1 wk, then acclimated to the darkened chamber for 3 days prior to measurement of to,. A 3-day acclimation period was necessary to achieve consistent results (Fig. 1). The flow-through chambers were placed in refrigerated cooling baths and their temperatures kept at 5.5 ( + 0.5) ‘C. During measurement of to, the chambers were sealed for periods of 6 to 24 h depending on the rate of oxygen consumption. Background oxygen levels were not allowed to fall below 3.0 ml * 1-l during the measurement of to,. Oxygen concentrations must be below 3.0 ml - 1- ’ before LO, is affected by background oxygen levels (Fig. 1). Triplicate measurements of fi0, were made for each fish and the three results averaged to provide an estimate of oxygen consumption. Oxygen measurements were made with an electronic oxygen probe and meter calibrated against Winkler titrations (Parsons et al., 1984).
L
OXYGEN
:
6
5
4
3
2
1
2
4
0
a
10
12
3
0
NUMBER
CONCENTRATION
DAYS
IN
(ml/l)
CHAMBER
Fig. 1. Oxygen consumption of starved Theragru chalcogramma at 5-6 “C relative to the number of days in the respiration chamber (solid line) and to background oxygen levels (dashed line).
289
POLLOCK RESPIRATION
Measurements of to, relative to water temperature were accomplished using 50to 90-g fish at seven temperatures ranging from 1.0 to 12.0 ‘C. Pollock within this weight range have similar rates of oxygen consumption (Fig. 2). The methods were similar to those used to examine the effect of fish size on k0,. The number of fish for which k0, were measured at each test temperature is given with the data. Estimates of energy expenditure due to respiration were calculated using a conversion factor of 4.63 x lo-’ cal. ~1~ l of 0, consumed (Brett & Groves, 1979).
. a-
.
: .
:.
. : .
.
l. . :
.
2
.
.
Cl
4 50
60
70
LIVE WEIGHT
80
90
(g)
Fig. 2. Specificoxygen consumptionof unfed 50- to 90-g 7’herugrachalcogramma at 5.5 “C.
RESULTS
The rate of oxygen consumption at 5.5 “C for fish weighing 6 to 300 g was best described for untransformed measurements by the power equation (Equation 1): plG2.g-1.h-1 = 165.379 (g wet ~t)-~.“; r = 0.87 (Fig. 3). When linear regression of the logarithm of oxygen consumption (~1. h - ’ ) on corresponding individual fish body weight is calculated, the Equation (2): log ~10,. fish- ’ * h- ’ = 2.2 + 0.755 (logg wet wt) was obtained with r = 0.99 and the SD of the regression coefficient = 0.007. At 5.5 “C, the metabolic rate Equation (3): cal. day- ’ = 99.958 + 4.393 (g wet wt); r = 0.96 was obtained based on indirect calorimetry. Measurements of t-0, relative to water temperature, for 40- to 90-g fish, exhibited a linear increase between 1 and 7.5 “C described by the Equation (4): PO, in ~10, *g- ’ *h- ’ = 12.617 + 7.961 (temp. “C); r = 0.98 and the SD of the regression coefficient = 0.65 (Fig. 4). Between 7.5 and 12 “C, measurements of to, did not increase and mean values had a range of 0.66 to 0.75 ~10, *g- ’ . h- I, respectively (Fig. 4). The estimate for Q,,, 1.0 to 12 “C, was 2.54 while Q,,, 1 to 7.5 “C was 6.04.
A.J. PAUL
290
E Oil__ 0
Y
50
100
BODY
200
WEIGHT
300
(g)
Fig. 3. Specific oxygen consumption of unfed Theragra chalcogramma (6-300 g) relative to body weight measured at 5.5 “C.
-
z 5 g
200
i_. 0
2
\,I,\I,I,,. 4
6
a
t0
12
14 ‘I
0 TEMPERATURE
(” C)
Fig. 4. Specific oxygen consumption of unfed 50-90 g Theragra chdcogramma relative to water temperature: mean and SD with number of fish in parentheses.
DISCUSSION
Like many cold water gadids, Theragra chalcogramma undergoes a winter starvation period accompanied by a marked loss in body weight and condition factor (Chen, 1983). During the winter, juvenile Bering Sea pollock move from 4 to 5 “C water into the midshelf domain (Iverson et al., 1979) where zooplankton prey are scarce (Cooney, 1981), and temperatures of 2 to 3 “C are common (Chen, 1983). The daily metabolic
POLLOCK RESPIRATION
291
energy needs of juvenile pollock are reduced m 18 % for every degree C decline in water temperature (Fig. 4). M~ten~ce rations for 45-g pollock, based on 30-day laboratory feeding experiments at 3 and 7.5 “C, have been previously estimated at 225 and 382 cal -day- ‘, respectively (Smith et al., 1986). These results are comparable to the 290 cal .day- ’ estimated for a 45-g pollock at 5.5 “C (Equation 2). Another estimate of energy needs can be dete~ned from weight loss during starvation. Juvenile pollock with a condition factor similar to those fish used in the experiments of Smith et al. (1986) contain 4.9 kcal . g dry wt- ’ and have a moisture content of 80% (Harris et al., in press). At 5.5 ‘C starved laboratory pollock lose ~0.3 g wet wt. day _ ’ (Smith et al., 1986) which would equal w 294 cal * day- ’ loss (Harris et al., in press). Maintenance rations for 34and 61-g Atlantic cod, Gad= morhua, at % 12 “C are 370 and 500 cal*day- ’ (Jones & Hislop, 1978). At 12 “C juvenile pollock of the same size would have similar maintenance rations, 249 and 447 cal . day - ’ (Fig. 4). It should be remembered, however, that estimates of energy requirements, based on laboratory experiments, require unknown adjustments to be applied to the ocean env~onment. Measurements for unfed pollock PO, must be considered minimum estimates for metabolism in the field. Depending on the level of feeding, activity and temperature, metabolic rates of Atlantic cod are two to three times the resting metabolic rate (Soofiani & Hawkins, 1982, 1985; Soofiani & Priede, 1985). When pollock were fast put in respiration chambers they were in an excited state, and their rates of PO, were 2.5 times higher than those recorded after the fish had acclimated 3 days (Fig. 1). Thus, like cod, active metabolic rates of pollock may be two to three times nonfeeding values. Only one other published measurement of oxygen consumption for juvenile pollock is available; 156 ~1. g- ’ *h- ’ for a 3.9-g fish at 12.5 “C (Fukuchi, 1976). A similar value, 142 ~1. g- i *h- ’ for a 3.9-g fish, was obtained from equations in this report. Few reports on thermal modification of gadid metabolic rates at the lower temperatures inhabited by pollock, 0 to 7 “C, are available for comparison with this study. Sootiani & Hawkins (1982; their Fig. 6) provide PO, measurements for unfed juvenile Atlantic cod at 7 to 18 ‘C. Their metabolic rate curve for cod is similar to that of pollock (Fig. 4), but the peak of the curve is at 15 instead of 8 “C for pollock. Estimates of Q10 = 2.48 (Saunders, 1963) and slope values of 0.79 to 0.88 (Saunders, 1963 ; Edwards et al., 1972) reported for G. mo~h~a, were very similar to those observed for pollock (Equation 2) in this study. Atlantic cod, like pollock, also exhibit decreased oxygen consumption rates at the upper portion of their thermal habitat. In G. morhua, there was a greater rise in PO, from 3 to 10 “C than from 10 to 15 “C (Saunders, 1963).The lack of significant rise in fi0, at the warmer temperatures of their habitat may be an energy conservation strategy in gadids or it could be the result of peaking of spontaneous activity at a given temperature. The failure of to, to increase at or above 8 ’ C (Fig. 3) may indicate that the preferred thermal habitat of juvenile Alaska pollock does not exceed this temperature even though the species is capable of surviving under much warmer conditions. Distribution data for Bering Sea pollock also suggests this;
292
A. J. PAUL
major concentrations of juveniles are found in 1 to 5 ‘C areas during the feeding season (Chen, 1983). The results of this study supplement previous studies on the energetic requirements of juvenile pollock. Estimates of metabolic energy needs can now be made for juvenile pollock over the temperature range inhabited by Alaskan pollock. However, there remain several aspects of this subject that need continued examination. Among them are measurements of gastric evacuation and energy requirements for feeding metabolism, swimming, excretion rate, in situ growth and somatic energy content on a seasonal basis. Similar information is also needed for the adult phase of the species.
ACKNOWLEDGEMENTS
This research was sponsored by the Alaska Sea Grant College Program, cooperatively supported by NOAA, Office of Sea Grant and Extramural programs, Department of Commerce, under Grant No. NA82AA-D-00044, project R/06-23 and the University of Alaska with funds appropriated by the state. Additional financial support was provided by the National Science Foundation PROBES Grant DPP 7623340. Facilities were provided by the University of Alaska, Institute of Marine Science, Seward Marine Center. Dr. R.L. Smith and R. Highsmith kindly reviewed the manuscript.
REFERENCES BRETT,J.R. & T.D. D. GROVES,1979. Physiological energetics. In, Fishphysiology, Vol. 8, Bioenergericr and growth, edited by W.E. Hoar & D. J. Randall, Academic Press, New York, pp. 280-352. CHEN, L.F., 1983. The effects of water temperature on the seasonal distribution and growth of walleye pollock, Theragra chulcogrumma (Pallas), in the southeast Bering Sea. M.Sc. thesis, University of Alaska, Fairbanks, 92 pp. COONEY,R.T., 1981. Bering Sea zooplankton and micronekton communities with emphasis on annual production. In, The eastern Sering Sea shelf: oceanography and resources, Vol. 2, edited by D. W. Hood & J. A. Calder, U.S. Department of Commerce, N.O.A.A. Office of Marine Pollution Assessment, Washington, D.C., pp. 947-974. EDWARDS, R.C.C., D.M. FINLAYSON& J.H. STEELE, 1972. An experimental study of the oxygen consumption, growth, and metabolism of the cod (Gadus morhua L.). J. Eq. Mar. Biol. Ecol., Vol. 8, pp. 299-309. FUKUCHI, M., 1976. Some aspects of bioenergetics of walleye pollock (Theragrc chalcogrumma Pallas) at early life stages. Ph.D. thesis, University of Hokkaido, Hakodate, Japan, 60 pp. HARRIS, R.K., T. NISHIYAMA& A. J. PAUL, in press. Carbon, nitrogen and caloric content of eggs, larvae, and juveniles of the walleye pollock, Theragra chalcogramma. J. Fish Biol. IVERSON,R. L., L.K. COACHMAN,R.T. MOONEY,T. S. ENGLISH, J. J. GOERING,G. L. HUNT, JR., M.C. MACAULEY+ C. P. MCROY, W. S. REEBURG& T. E. WHITLEDGE,1979. Ecological significance of fronts in the southeast Bering Sea. In, Ecological processes in coastal and marine systems, edited by R. J. Livingston, Plenum Press, New York, pp. 437-466. JONES, R. & J.R.G. HISLOP, 1978. Further observations on the relation between food intake and growth of gadoids in captivity. J. Cons., Cons. Int. Explor. Mer, Vol. 38, pp. 244-251. LAEVASTU,T. & H.A. LARKINS, 1981. MarinejTsheries ecosystem, its simulation and management. Fishing News .Books Ltd., Famham, England, 162 pp. PARSONS,T. R., Y. MAITA & C.M. LALLI, 1984. A manual of chemical and biological methodr for seawater analysis. Pergamon Press, Oxford, England, 184 pp.
POLLOCK RESPIRATION
293
PAUL,A. J., 1983.Light, temperature, nauplii concentrations, and prey capture by first feeding pollock larvae Theragra chalcogramma. Mar. Ecol. Prog. Ser., Vol. 13, pp. 175-179. PEREYRA,W., J. REEVES& R. BAKKALA,1976. Demersal fish and shellfish resources of the eastern Bering Sea in the baseline year 1975. U.S. Natl. Mar. Fish. Serv., Northwest and Alaska Fish. Cent., Seattle, WA Processed Report, 6 19 pp. SAUNDERS,R.L., 1963. Respiration of the Atlantic cod. J. Fish. Res. Board Can., Vol. 20, pp. 373-386. SMITH, R.L., A. J. PAUL & J.M. PAUL, 1986. Effect of food intake and temperature on growth and conversion efficiency in juvenile walleye pollock, Theragra chalcogramma (Pallas), a laboratory study. J. Cons., Cons. int. Explor. Mer, in press. SOOFIANI,N.M. & D.A. HAWKINS, 1982. Energetic costs at different levels of feeding in juvenile cod, (Gadus morhua). J. Fish Biol., Vol. 21, pp. 577-592. SOOFIANI, N.M. & D.A. HAWKINS, 1985. Field studies of energy budgets. In, Fish energetics: new perspectives, edited by P. Tytler & P. Calow, Johns Hopkins University Press, Maryland, pp. 283-307. SOOFIANI,N. M. & I. G. PRIEDE, 1985. Aerobic metabolic scope and swimming performance in juvenile cod, Gadus morhua L. J. Fish Biol., Vol. 26, pp. 127-138. YOSHIDA,H. & Y. SAKURAI, 1984. Relationship between food consumption and growth of adult walleye pollock Theragra chalcogramma in captivity. Bull. Jpn. Sot. Sci. Fish., Vol. 50, pp. 763-769.
287
Elsevier
JEM 670
RESPIRATION OF JUVENILE POLLOCK, THERAGRA
CHALCOGRAMMA
(Pallas), RELATIVE TO BODY SIZE AND TEMPERATURE’
A.J. PAUL University of Alaska, Institute of Marine Science, Seward Marine Center, P.O. Box 730, Seward, Alaska 99664, U.S.A.
(Received 27 November 1985; revision received 12 February 1986; accepted 14 February 1986) Abstract: Measurements of oxygen consumption by starved juvenile pollock, Theragra chalcogramma (Pallas), relative to body size and water temperature were determined. Oxygen consumption rates for 6-300 g pollock were described by the equation: log ~10,. h- ’ = 12.78 + 0.755 (logg wet wt) at 5.5 “C. The temperature range normally experienced by this species in Aiaska is 1-12 “C. Weight specific oxygen consumption (yOl) for 40-9Og fish exhibited a Iinear increase between 1 and 7.5_“C described by the equation: PO, (pl*g-‘.h-‘)= 12.617 + 7.961 (temp. “C). Values for specific VO, were similar between 7.5 and 12°C. The estimate for Q,, (1-12 “C) was 2.5, similar to other cold-water fish. The daily energy expenditure due to respiration for unfed fish is calculated and compared to other existing estimates. Key words: oxygen consumption; energy requirements; Theragra cha~~~~~mrna
INTRODUCTION
The pollock, Therugra c~~ZC~~~~~~, is an important commercial species and forage fish in Alaskan waters. In the southeastern Bering Sea it constitutes 20 to 50% of the total fish community biomass (Pereyra et al., 1976). The total commercial catch averaged 4.4 million metric tons a year during the 1970’s. Pollock are major food items in the diets of marine mammals, birds and several fish species. Currently, yield models are being constructed to provide harvest guidelines for pollock (Laevastu & Larkins, 198 1). These models and ecological studies of Alaskan marine systems require estimates of pollock energy requirements. Recent studies have provided some energetic estimates (Fukuchi, 1976; Paul, 1983; Yoshida & Sakurai, 1984; Smith et al., 1986; Harris et aZ., in press), but none of these experiments was carried out utilizing the entire range of temperatures that this species encounters in Alaska. Furthermore, in each of the studies only a limited size range of fish were used in experiments. Thus, with the existing ~fo~ation, it is difficult to estimate energetic needs of pollock relative to their body size and the water temperature. The objective of this study was to provide additional information on pollock metabolic energy needs by measuring specific oxygen consumption rates (PO,) ’ Contribution Number 609 from the institute of Marine Science, University of Alaska. 0022-0981/86/$03.50 0 1986 Elsevier Science Publishers B.V. (Biomedical Division)
A. J. PAUL
288
of juvenile pollock as a function of fish size (6 to 300 g) within the range of water temperature they normally experience. In the southeastern Bering Sea, juvenile pollock primarily inhabit water between 0 and 7 “C, with a range of - 1.2 to 11.2 “C (Chen, 1983).
MATERIALS
AND
METHODS
Weight related oxygen consumption was measured for 15 fish, 6 to 300 g, at 5 to 6 ‘C. Fish under 135 g were held in a 23.5-l respiration chamber and larger fish in 208-l chambers. Fish were kept at test temperatures for at least 2 wk, not fed for 1 wk, then acclimated to the darkened chamber for 3 days prior to measurement of to,. A 3-day acclimation period was necessary to achieve consistent results (Fig. 1). The flow-through chambers were placed in refrigerated cooling baths and their temperatures kept at 5.5 ( + 0.5) ‘C. During measurement of to, the chambers were sealed for periods of 6 to 24 h depending on the rate of oxygen consumption. Background oxygen levels were not allowed to fall below 3.0 ml * 1-l during the measurement of to,. Oxygen concentrations must be below 3.0 ml - 1- ’ before LO, is affected by background oxygen levels (Fig. 1). Triplicate measurements of fi0, were made for each fish and the three results averaged to provide an estimate of oxygen consumption. Oxygen measurements were made with an electronic oxygen probe and meter calibrated against Winkler titrations (Parsons et al., 1984).
L
OXYGEN
:
6
5
4
3
2
1
2
4
0
a
10
12
3
0
NUMBER
CONCENTRATION
DAYS
IN
(ml/l)
CHAMBER
Fig. 1. Oxygen consumption of starved Theragru chalcogramma at 5-6 “C relative to the number of days in the respiration chamber (solid line) and to background oxygen levels (dashed line).
289
POLLOCK RESPIRATION
Measurements of to, relative to water temperature were accomplished using 50to 90-g fish at seven temperatures ranging from 1.0 to 12.0 ‘C. Pollock within this weight range have similar rates of oxygen consumption (Fig. 2). The methods were similar to those used to examine the effect of fish size on k0,. The number of fish for which k0, were measured at each test temperature is given with the data. Estimates of energy expenditure due to respiration were calculated using a conversion factor of 4.63 x lo-’ cal. ~1~ l of 0, consumed (Brett & Groves, 1979).
. a-
.
: .
:.
. : .
.
l. . :
.
2
.
.
Cl
4 50
60
70
LIVE WEIGHT
80
90
(g)
Fig. 2. Specificoxygen consumptionof unfed 50- to 90-g 7’herugrachalcogramma at 5.5 “C.
RESULTS
The rate of oxygen consumption at 5.5 “C for fish weighing 6 to 300 g was best described for untransformed measurements by the power equation (Equation 1): plG2.g-1.h-1 = 165.379 (g wet ~t)-~.“; r = 0.87 (Fig. 3). When linear regression of the logarithm of oxygen consumption (~1. h - ’ ) on corresponding individual fish body weight is calculated, the Equation (2): log ~10,. fish- ’ * h- ’ = 2.2 + 0.755 (logg wet wt) was obtained with r = 0.99 and the SD of the regression coefficient = 0.007. At 5.5 “C, the metabolic rate Equation (3): cal. day- ’ = 99.958 + 4.393 (g wet wt); r = 0.96 was obtained based on indirect calorimetry. Measurements of t-0, relative to water temperature, for 40- to 90-g fish, exhibited a linear increase between 1 and 7.5 “C described by the Equation (4): PO, in ~10, *g- ’ *h- ’ = 12.617 + 7.961 (temp. “C); r = 0.98 and the SD of the regression coefficient = 0.65 (Fig. 4). Between 7.5 and 12 “C, measurements of to, did not increase and mean values had a range of 0.66 to 0.75 ~10, *g- ’ . h- I, respectively (Fig. 4). The estimate for Q,,, 1.0 to 12 “C, was 2.54 while Q,,, 1 to 7.5 “C was 6.04.
A.J. PAUL
290
E Oil__ 0
Y
50
100
BODY
200
WEIGHT
300
(g)
Fig. 3. Specific oxygen consumption of unfed Theragra chalcogramma (6-300 g) relative to body weight measured at 5.5 “C.
-
z 5 g
200
i_. 0
2
\,I,\I,I,,. 4
6
a
t0
12
14 ‘I
0 TEMPERATURE
(” C)
Fig. 4. Specific oxygen consumption of unfed 50-90 g Theragra chdcogramma relative to water temperature: mean and SD with number of fish in parentheses.
DISCUSSION
Like many cold water gadids, Theragra chalcogramma undergoes a winter starvation period accompanied by a marked loss in body weight and condition factor (Chen, 1983). During the winter, juvenile Bering Sea pollock move from 4 to 5 “C water into the midshelf domain (Iverson et al., 1979) where zooplankton prey are scarce (Cooney, 1981), and temperatures of 2 to 3 “C are common (Chen, 1983). The daily metabolic
POLLOCK RESPIRATION
291
energy needs of juvenile pollock are reduced m 18 % for every degree C decline in water temperature (Fig. 4). M~ten~ce rations for 45-g pollock, based on 30-day laboratory feeding experiments at 3 and 7.5 “C, have been previously estimated at 225 and 382 cal -day- ‘, respectively (Smith et al., 1986). These results are comparable to the 290 cal .day- ’ estimated for a 45-g pollock at 5.5 “C (Equation 2). Another estimate of energy needs can be dete~ned from weight loss during starvation. Juvenile pollock with a condition factor similar to those fish used in the experiments of Smith et al. (1986) contain 4.9 kcal . g dry wt- ’ and have a moisture content of 80% (Harris et al., in press). At 5.5 ‘C starved laboratory pollock lose ~0.3 g wet wt. day _ ’ (Smith et al., 1986) which would equal w 294 cal * day- ’ loss (Harris et al., in press). Maintenance rations for 34and 61-g Atlantic cod, Gad= morhua, at % 12 “C are 370 and 500 cal*day- ’ (Jones & Hislop, 1978). At 12 “C juvenile pollock of the same size would have similar maintenance rations, 249 and 447 cal . day - ’ (Fig. 4). It should be remembered, however, that estimates of energy requirements, based on laboratory experiments, require unknown adjustments to be applied to the ocean env~onment. Measurements for unfed pollock PO, must be considered minimum estimates for metabolism in the field. Depending on the level of feeding, activity and temperature, metabolic rates of Atlantic cod are two to three times the resting metabolic rate (Soofiani & Hawkins, 1982, 1985; Soofiani & Priede, 1985). When pollock were fast put in respiration chambers they were in an excited state, and their rates of PO, were 2.5 times higher than those recorded after the fish had acclimated 3 days (Fig. 1). Thus, like cod, active metabolic rates of pollock may be two to three times nonfeeding values. Only one other published measurement of oxygen consumption for juvenile pollock is available; 156 ~1. g- ’ *h- ’ for a 3.9-g fish at 12.5 “C (Fukuchi, 1976). A similar value, 142 ~1. g- i *h- ’ for a 3.9-g fish, was obtained from equations in this report. Few reports on thermal modification of gadid metabolic rates at the lower temperatures inhabited by pollock, 0 to 7 “C, are available for comparison with this study. Sootiani & Hawkins (1982; their Fig. 6) provide PO, measurements for unfed juvenile Atlantic cod at 7 to 18 ‘C. Their metabolic rate curve for cod is similar to that of pollock (Fig. 4), but the peak of the curve is at 15 instead of 8 “C for pollock. Estimates of Q10 = 2.48 (Saunders, 1963) and slope values of 0.79 to 0.88 (Saunders, 1963 ; Edwards et al., 1972) reported for G. mo~h~a, were very similar to those observed for pollock (Equation 2) in this study. Atlantic cod, like pollock, also exhibit decreased oxygen consumption rates at the upper portion of their thermal habitat. In G. morhua, there was a greater rise in PO, from 3 to 10 “C than from 10 to 15 “C (Saunders, 1963).The lack of significant rise in fi0, at the warmer temperatures of their habitat may be an energy conservation strategy in gadids or it could be the result of peaking of spontaneous activity at a given temperature. The failure of to, to increase at or above 8 ’ C (Fig. 3) may indicate that the preferred thermal habitat of juvenile Alaska pollock does not exceed this temperature even though the species is capable of surviving under much warmer conditions. Distribution data for Bering Sea pollock also suggests this;
292
A. J. PAUL
major concentrations of juveniles are found in 1 to 5 ‘C areas during the feeding season (Chen, 1983). The results of this study supplement previous studies on the energetic requirements of juvenile pollock. Estimates of metabolic energy needs can now be made for juvenile pollock over the temperature range inhabited by Alaskan pollock. However, there remain several aspects of this subject that need continued examination. Among them are measurements of gastric evacuation and energy requirements for feeding metabolism, swimming, excretion rate, in situ growth and somatic energy content on a seasonal basis. Similar information is also needed for the adult phase of the species.
ACKNOWLEDGEMENTS
This research was sponsored by the Alaska Sea Grant College Program, cooperatively supported by NOAA, Office of Sea Grant and Extramural programs, Department of Commerce, under Grant No. NA82AA-D-00044, project R/06-23 and the University of Alaska with funds appropriated by the state. Additional financial support was provided by the National Science Foundation PROBES Grant DPP 7623340. Facilities were provided by the University of Alaska, Institute of Marine Science, Seward Marine Center. Dr. R.L. Smith and R. Highsmith kindly reviewed the manuscript.
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