The bioenergetic costs of specific dynamic action and ammonia excretion in a freshwater predatory leech Nephelopsis obscura

Camp. Biochem. Physiol. Vol. lOgA, No. 4, pp. 523-531, 1994 Copyright 0 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0300-9629/94 $7.00 + 0.00

Pergamon

The bioenergetic costs of specific dynamic action and ammonia excretion in a freshwater predatory leech Nephelopsis obscura V. Kalarani

and Ronald

W. Davies

Division of Ecology (Aquatic Ecology Group), Department of Biological Sciences, The University of Calgary, Calgary, Alberta, Canada T2N lN4 The energy utilized by the predatory freshwater leech for specific dynamic action (SDA) and exogenous excretion, and the proportion of absorbed energy available for growth and/or activity were determined at 5, 10, 15, 20 and 25OC. SDA and exogenous ammonia excretion increased with increases in temperature to 20°C but decreased at 25OC. The duration of SDA decreased from 19 hr at 5OC to 11 hr at 25OC, while the duration of exogenous excretion decreased from 22 hr at 5OC to 11 hr at 25OC. The proportion of absorbed energy utilized for SDA and exogenous excretion decreased from 5OC to 15OC and increased at 25OC; however the energy available for growth and activity increased from 7.4 J/day at 5OC to a maximum of 32.6 J/day at 15OC, decreasing to 12.7 J/day at 25OC. Key words: Bioenergetic Nephelopsis obscura.

costs; Ammonia

Comp. Biochem. Physiol. IOBA, 523-531,

excretion;

Specific dynamic

action (SDA);

1994.

Introduction Energy costs of digestion, absorption and biochemical transformation of absorbed food are termed specific dynamic action (SDA) (Kleiber, 1961) and are usually measured as an increase in oxygen consumption. Deamination of amino acids during SDA (Borsook, 1936; Beamish et al., 1975) results in the formation of nitrogenous end products which are excreted (exogenous excretion), immediately resulting in additional energy losses (Brett and Zala, 1975; From and Rasmussen, 1984; Ramanarine et al., 1987). Ammonia is the Correspondence to: R. W. Davies, Division of Ecology (Aquatic Ecology Group), Department of Biological Sciences, The University of Calgary, Calgary, Alberta, Canada, T2N lN4. Fax: 403289-93 1 I. Received 21 July 1993; accepted 17 September 1993. 523

major excretory product in freshwater invertebrates since it is readily eliminated from the body (Pandian, 1987; Randall and Wright, 1987; Zebe et al., 1986). Different energy consuming processes within an animal compete for the same source of energy, and the amounts of absorbed energy utilized for SDA and excretion determine the energy available for growth and/or metabolism. Although simultaneous increases in oxygen consumption and ammonia excretion, indicating increased energy costs, following food ingestion have been observed in several species (Brett and Zala, 1975; Caulton, 1978; Zebe et al., 1986; Davenport et al., 1990; Gonz& lez et al., 1990), they are usually ignored in the calculation of bioenergetic budgets. Like most aquatic organisms in temperate climates, Nephelopsis obscura Verrill

524

V. Kalarani and Ronald W. Davies

(Erpobdellidae), a predatory leech widely distributed in the lentic freshwater ecosystems of Canada and northern parts of the United States, experiences temperature fluctuations on a seasonal basis (Davies, 1991). Over 5-25°C representative annual field temperatures, the amount of energy utilized for SDA and exogenous excretion by N. obscura is determined and the proportion of absorbed energy available for growth and/or activity calculated at each temperature.

Materials and Methods Post-hatchling (8-10 mg) N. obscura were collected in July from Stephenson’s Pond, a small (2.2 ha) pothole pond located 5 km northwest of Calgary, Alberta, and maintained for 2 weeks at 20°C in filtered, aerated (100% saturation) pond water with a 12 hr : 12 hr light-dark regime and ad libiturn prey (Tubifex tubifex (Miiller)) three times a week for 1 hr. When they had grown to 25 + 2 mg, four groups of leeches (N = 25) were slowly acclimated (l”C/day) to one of four experimental temperatures (5, 10, 15 and 25°C) with an additional group (N = 25) maintained at 20°C. All the leeches were fed ad libitum during and after acclimation until they reached 40 + 5.0 mg. At each temperature, two subgroups of leeches (N = 5) were starved for 48 hr. The resting (Rm) and active (Ra) oxygen consumption (,ulO*/hr) of one subgroup (unfed N. obscura) were measured every minute for 24 hr using a computerized flowthrough respirometer (Davies et al., 1992). Aerobic scope (AS), the amount of energy available to an organism through aerobic metabolism beyond that needed for maintenance (Fry, 1947) was calculated as the difference between Ra and Rm. Simultaneously, ammonia and urea excretion (mg/hr) were measured hourly following Solorzano (1969) in 10 ml water samples collected from each respiration chamber. The second subgroup of leeches were individually supplied with 100 mg of T. tubzfex for 1 hr (fed N. obscuru) and the amount ingested was calculated from the difference in weights of T. tubifex at the start and end of the feeding period. Energy losses in faeces plus mucus were measured

0.6 ,

0.0

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TEMPERATURE

Fig. 1. Mean (+ SD) energy costs of resting (m) and active (0) oxygen consumption (J/hr) of unfed Neph elopsis obscura (N = 5) at 5, 10, 15, 20 and 25°C.

following Dratnal and Davies (1990) and absorbed energy at each temperature was calculated as the difference between ingested energy and the energy lost in faeces plus mucus. Rm and Ra were measured every minute and ammonia every hour for 24 hr. Rm, Ra and AS were converted to energy equivalents using an oxygen coefficient of 0.0202 J/plOz/hr (Elliott and Davison, 1975) while the amounts of ammonia excreted and food ingested were converted to energy equivalents using the coefficients of 20.44 J/mg NH3 (Elliott and Davison, 1975) and 23.1 J/mg DWT food, respectively. At each temperature, SDA was calculated as the difference between the energy costs of Rm in the fed and unfed N. obscuru. As no detectable quantities of urea were found, the energy loss in ammonia excretion of unfed N. obscuru was 0.10

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Fig. 2. Mean ( f SD) energy loss (J/ hr) in endogenous excretion in unfed Nephelopsis obscura (N = 5) at 5, 10, 15, 20 and 25’C.

525

Bioenergetic costs of SDA and ammonia excretion

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Fig. 3. Mean (*SD)

hourly changes in energy costs (J) of resting respiration and fed (A) Nephelopsis obscura (N = 5) over 24 hr.

considered the cost of endogenous excretion, and the difference between the energy loss of ammonia excretion of fed and unfed N. obscura as the cost of exogenous excretion. Differences in Rm, Ra, AS and ammonia excretion of both unfed and fed N. obscura were assessed using one-way ANOVA. Twoway analysis of variance was used for comparisons between Rm, Ra, AS and ammonia excretion of unfed and fed N. obscuru over time. Comparisons between unfed and fed N. obscura at any given time were made using Student’s t-test. In all statistical analyses, significance was assessed at P < 0.05 level.

of unfed (a)

Results Rm, Ra and AS (Fig. 1) and endogenous ammonia excretion (Fig. 2) of unfed N. obscura increased with temperature from 5 to 20°C but decreased at 25°C. No significant differences were observed over 24 hr at any of the five temperatures (Figs 3,4,5 and 6). Energy ingested, energy lost in faeces plus mucus and energy absorbed increased with the increase in temperature from 5 to 15°C but decreased at 20 and 25°C (Table 1). At all temperatures, Rm of fed N. obscura increased significantly immediately after feeding, followed by a gradual decrease to the prefeeding level (Fig. 3). Ra of fed and

526

V. Kalarani and
unfed N. obscura were not significantly different at any temperature (Fig. 4) but AS of N. obscura were significantly lower (Fig. 5). Elevation of ammonia excretion occurred with a delay of 2 hr at 5°C 4 hr at 10°C and 1 hr at 15, 20 and 25°C following feeding (Fig. 6). SDA and exogenous ammonia excretion increased with the increase in temperature from 5 to 20°C and decreased at 25°C (Tables 2 and 3). The duration of SDA decreased from 19 hr at 5°C to 11 hr at 25°C and the duration of exogenous excretion decreased from 22 hr at 5°C to 11 hr at 25°C. The total energy utilized for SDA and exogenous excretion increased from 5 to 20°C but decreased at 25°C but the proportion of absorbed energy utilized for SDA

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and exogenous excretion decreased from 10.3% at 5C to 6.1% at 15°C and increased to 10.3% at 25°C (Table 4).

Discussion Significant increases in Rm, Ra and endogenous excretion of unfed N. obscura from 5 to 20°C indicate higher metabolic demands with increases in temperature (Figs 1 and 2). The decreases in Rm, Ra and AS at 25°C suggest that either oxygen becomes limiting or N. obscura is close to its upper limit of temperature tolerance. Similar observations have been made in other species (Brett, 1964; Fry, 1971; Rutledge and Pritchard, 1981). Increased endogenous excretion in N. obscura with the increase

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Fig. 4. Mean (+ SD) hourly changes in energy costs (J) of active respiration fed (A) Nephelopsis obscura (N = 5) over 24 hr.

of unfed (0)

and

Bioenergetic costs of SDA and ammonia excretion

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Fig. 5. Mean ( f SD) hourly changes in aerobic scope (J) in unfed (0) and fed (A) Nephelopsis obscura (N = 5) over 24 hr.

in temperature indicates an increased catabolism and turnover of body protein due to higher energy demands. No endogenous die1 rhythms in Rm (Fig. 3), Ra (Fig. 4), AS (Fig. 5) or endogenous excretion (Fig. 6) were observed in unfed N. obscura.

Increases in ingestion with the increase in temperature from 5 to 15°C and the decrease at 20 and 25°C (Table 1) supports the view of Brett (1979) and Elliott (1979) that food consumption declines as the temperature approaches the upper lethal limit. The increase in absorption efficiency with the increase in temperature is common among fish species (Brocksen and Brugge, 1974; Allen and Wootton, 1983). Although ingestion and absorption decreased at 2O”C, N.

obscura showed an increase in the proportion of energy absorbed with the increase in temperature to 20°C. Because of the high food ingestion at 15”C, N. obscura had the highest amount of energy absorbed despite having the highest energy losses in faeces plus mucus. Ammonia excretion did not increase immediately after feeding but like Rm decreased to the unfed level within 24 hr (Figs 3 and 6). Food ingestion had no effect on Ra (Fig. 4) however the increased Rm following feeding resulted in reduced AS at all temperatures (Fig. 5). Similarly, Vahl and Davenport (1979), Soofiani and Hawkins (1982) and Jobling (1981) recorded little capacity for activity (i.e. low AS) in fed fish.

V. Kalarani and Ronald W. Davies

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Fig. 6. Mean (+ SD) hourly changes in energy costs of ammonia excretion fed (A) Nephelopsis obscura (N = 5) over 24 hr.

SDA and exogenous ammonia excretion of Nephelopsis obscura represent increases in metabolic costs which must be considered in the bioenergetic budget. The energy costs of SDA increase with meal sizes (Table 2) and with temperature between 5

Table

in unfed (a)

and 20°C. Although there is a significant increase in absorbed energy with temperatures up to 15”C, as there is a progressive decrease in the duration of SDA with increases in temperature (Table 2), it appears that the duration of SDA is related not just

1. Mean energy ingested, lost in faeces plus mucus (Fe + Mu) and absorbed by Nephelopsis obscura at different temperatures

Temperature 5 10 15 20 25

(“C)

Ingested 16.5 23.0 51.1 40.3 25.4

(J)

&- 1.6 + 1.9 + 2.8 + 2.0 + 1.6

Mean f SD. N = 5. Percentage

and

Fe + Mu (J) 5.1 + 0.6 (30.9) 5.7 + 0.4 (24.8) 9.4+3.4(18.4) 6.1 + 1.4 (15.1) 6.2 + 2.2 (24.5)

of ingested

Absorbed

(J)

11.6 f 1.3 (69.1) 17.5 f 1.5 (75.2) 41.9+ 1.8(81.6) 34.2 &- 1.7 (84.9) 19.0 + 1.5 (75.5)

energy in parentheses.

Bioenergetic costs of SDA and ammonia excretion

529

Table 2. Mean energy costs of resting respiration (Rm) of fed and unfed Nephelopsis obscura, specific dynamic action (SDA) and duration of SDA at different temperatures SDA Energy costs of Rm (J) Temperature (“C) 5

10 15 20 25

cost

Duration

Unfed

Fed

(J)

(W

2.5 f 0.1 3.6 f 0.1

3.4 f 1.2 4.9 * 1.8

0.9 * 0.4

19

4.8 f 0.2 5.8 f 0.2 4.4 f 0.2

6.2 + 2.3 7.5 f 2.7 5.6 + 2.1

1.3 f 0.0 1.4f0.2 1.7fO.l 1.3 f 0.1

17 15 13 11

Mean f SD. N = 5.

to the quantity of food ingested, but could also be related to the rate of the passage of food through the gut and the products of digestion through the gut mucosa as observed in fish (Jobling and Davies, 1979, 1980). The longer duration of SDA in N. obscura at low temperatures reflects the slower rate of assimilation (Fig. 3; Table 2) with metabolic costs spread over a longer period. Although the duration of exogenous excretion was longer than SDA at each temperature (Tables 2 and 3), even at 5°C both were completed within 22 hr after feeding. In other animals, SDA is reported as lasting from a few hours (Muir and Niimi, 1972) to several days (Soofiani and Hawkins, 1982). Nitrogenous excretion in fish (Savitz, 1971; Brett and Zala, 1975) declined to prefeeding levels within 24 hr, although GuerinAncey (1976) recorded elevated levels of excretion lasting 6 days at 20°C and 8 days at 16°C.

The proportion of absorbed energy utilized for SDA and exogenous excretion in N. obscura was significant at each temperature (Table 4) with the energy available for growth and activity being influenced by the total cost of Rm, SDA, endogenous and exogenous excretion. The maximum energy (32.6 J/day or 77.8%) available for growth and activity occurred at 15”C, the optimum temperature for N. obxura in the field (Davies, 199 1). This study thus emphasizes the need for considering the costs of SDA and exogenous excretion as components of the energetic budget and indicates their importance to the understanding of the interrelationship between physiological responses of the organism and the energy ingested and absorbed. Acknowledgements-The

authors thank Y. Qian and P. Dratnal for their technical assistance and Dr D. C. Reddy for his comments on the manuscript.

Table 3. Mean energy costs of ammonia excretion of unfed (endogenous) and fed (endogenous plus exogenous) Nephelopsis obscura and duration of exogenous excretion at different temperatures Energy costs of excretion (J) ~ Temperature (“C) 5 10 15 20 25

Exogenous excretion

Unfed (endogenous)

Fed (endogenous +exogenous)

0.4 f 0.0 1.0 f 0.1 2.0fO.l 2.2 + 0.1 0.5 + 0.1

0.7 f 0.1 1.3 f 0.1 3.2 &-0.1 3.6 f 0.1 0.750.1

Mean f SD. N = 5.

cost (J)

Duration (hr), 22 0.3 * 0.0 18 0.3 fO.l 17 1.2kO.l 14 1.5 kO.1 II 0.2fO.l

V. Kalarani and Ronald W. Davies

530

Table 4. Mean energy utilized for resting respiration (Rm) and endogenous excretion (End) by unfed Nephelopsis obscura, and specific dynamic action (SDA), exogenous excretion (Ex) and energy available for growth and activity in fed Nephelopsis obscura at different temperatures Utilized Temperature (“C) 5 10 15 20 25

CJ/day)

Rm + End 2.94 4.62 6.76 8.09 4.88

+ 0.13 t_ 0.16 f 0.18 + 0.1 l 2 0.14

(25.4) (26.4) (16.1) (23.6) (25.7)

SDA + Ex 1.19 + 0.14(10.3) 1.55 _t 0.08 (8.9) 2.55 & 0.12(6.1) 3.03 F 0.07 (8.9) 1.48 _C0.11 (10.3)

Available for growth and activity (J/day) 7.44 f 11.34 + 32.61 + 23.11 + 12.65 f

1.O(64.3) 1.3 (64.8) 1.6 (77.8) I .2 (67.5) 0.9 (66.6)

Mean f SD. N = 5. Percentage of absorbed energy in parentheses.

References Allen J. R. M. and Wootton R. J. (1983) Rate of food consumption in a population of threespine sticklebacks, Gasterosteus aculeatus, estimated from the faecal production. Envir. Biol. Fish 8, 157-162. Beamish F. W. II., Niimi A. J. and Let P. F. K. P. (19’75) Bioenergetics of teleost fishes: environmental influences. In Comparative Physiology-Functional Aspects of Structural Materials (Edited by Bolis L., Maddrell H. P. and Schmidt-Nielsen K.), pp. 187-209. Amsterdam, North-Holland. Borsook H. (1936) The specific dynamic action of protein and amino acids in animals. Biol. Rev. 11, 147. Brett J. R. (1964) The respiratory metabolism and swimming performance of young sockeye salmon. J. Fish Res. Board Can. 21, 1183-1226. Brett J. R. (1979) Physiological energetics. In Fish Physiology (Edited by Hoar W. S., Randall D. J. and Brett J. R.), Vol. V, pp. 280-352. Academic Press, London. Brett J. R. and Zala C. A. (1975) Daily patterns of nitrogen excretion and oxygen consumption of sockeye salmon, Oncorhynchus nerka, under controlled conditions. J. Fish Res. Board Can. 32, 2479-2486.

Brockson R. W. and Brugge J. P. (1974) Preliminary investigations on the influence of temperature on food assimilation by rainbow trout, Saimo gairdneri Richardson. J. Fish Biol. 6, 93-97. Caulton M. S. (1978) The importance of habitat temperatures for growth in the tropical cichlid Tilapia rendalli Boulenger. J. Fish Biol. 13,99-l 12. Davenport J., Kjorsvik E. and Haug T. (1990) Appetite, gut transit, oxygen uptake and nitrogen excretion in captive Atlantic halibut, Hippoglossus hippoglossus L., and lemon sole, Microstomus kitt (Walbaum). Aquaculture 90, 267-277. Davies R. W. (1991) Annelida: leeches, polychaetes and acanthobdellids. In Ecology and Classification of North American Freshwater rnvertebrates (Edited by Thorpe J. H. and Covich A. P.), pp. 437479. Academic Press, New York. Davies R. W., Wrona F. J. and Kalarani V. (1992) Assessment of activity-specific metabolism of

aquatic organisms:

an improved system. Can. J.

Fish Aquat. Sci. 49, 1142-1148.

Dratnal E. and Davies R. W. (1990) Feeding and energy allocation in Nephelopsis obscura following exposure to winter stresses. J. Anim. Ecol. 59, 763-773.

Elliott J. M. (1979) Energetics of freshwater teleosts. In Fish Phenology: Anabolic Adaptiveness in Teleosts (Edited by Miller J. P.), pp. 2961. Symp. Zool. Sot. Lond. No. 44, Academic Press, London. Elliott J. M. and Davison W. (1975) Energy equivalents of oxygen consumption in animal energetics. Oecologia 19, 195-201. From J. and Rasmussen G. (1984) A growth model, gastric evacuation, and body composition in rainbow trout, Salmo gairdneri Richardson, 1836. Dana 3, 61-139. Fry F. E. J. (1947) Effects of the environment on animal activity. University of Toronto Studies in Biol. Series 55, 1-62. Fry F. E. J. (1971) The effect of environmental factors on the physiology of fish. In Fish Physiology (Edited by Hoar W. S. and Randall D. J.), Vol. 6, pp. 1-98. Academic Press, New York. Gonzalez M. L., Perez M. C., Lopez D. A. and Buitano M. S. (1990) Effect of temperature in the energy availability for growth of Concoiepas concoiepas (Brugiere). Rev. Biot. Mar. 25, 71-81. Guerin-Ancey 0. (1976) Etude experimentale de I’excretion azotee du bar (Dicentrarchus iabrax) en tours de croissance I. Effets de la temperature et du poids du corps sur l’excretion d’ammoniac et d’uree. Aquaculture 9, 71-80. Jobling M. and Davies P. S. (1979) Gastric evacuation in plaice, Pleuroneftes platessa L.: effects of temperature and meal size. J. Fish Biol. 14, 539-546.

Jobling M. and Davies P. S. (1980) Effects of feeding on metabolic rate, and the specific dynamic action in plaice, Pleuronectes platessa L. J. Fish Biol. 16, 629-638. Kleiber M. (1961) The Fire of Life. An rntroduction to Animal Energetics. John Wiley, New York. Muir B. S. and Niimi A. J. (1972) Oxygen consumption of the euryhaline fish aholehole (Kuhlia sanduicensis) with reference to salinity, swimming and

Bioenergetic costs of SDA and ammonia excretion

food consumption.

J. Fish Res. Board Can. 29,

67-71.

Pandian T. J. (1987) Fish. In Animal Bioenergetics, Vol. 2, Bivalvia through Reptilia. (Edited by Pandian T. J. and Vernberg F. J.), pp. 357465. Academic Press, San Diego. Ramanarine I. W., Pirie J. M., Johnstone A. D. F. and Smith G. W. (1987) The influence of size and feeding frequency on ammonia excretion by juvenile Atlantic cod, Gadus morhua L. J. Fish Biol. 31, 545-560.

Randall D. J. and Wright P. A. (1987) Ammonia distribution and excretion in fish. Fish Physiol. Biochem. 3, 107-l 20.

Rutledge P. S. and Pritchard A. W. (1981) Scope for activity in the crayfish Pacifastacus leniusculus. Am. J. Physiol. 240, R87-R92.

531

Savitz J. (1971) Nitrogen excretion annd protein consumption of the bluegill sunfish (Lepomis macrochirus). J. Fish. Res. Board Can. 28,449-451.

Solorzano L. (1969) Determination of ammonia in natural waters by the phenolhypochlorite method. Limnol. Oceanogr. 14, 799-801.

Soofiani N. M. and Hawkins A. D. (1982) Energetic costs at different levels of feeding in juvenile cod, Gadus morhua L. J. Fish Biol. 21, 577-592.

Vahl 0. and Davenport J. (1979) Apparent specific dynamic action of food in the fish Blennius pholis. Mar. Ecol. Prog. Ser. 1, 699. Zebe E., Franz-Josef R. and Barbara K. (1986) Metabolic changes in the medical leech Hirudo medicinalis following feeding. Comp. Biochem. Physiol. 84A, 49-55.