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The effects of temperature and salinity on the metabolic rate of juvenile Macrobrachium rosenbergii (Crustacea: Palaemonidae)
THE EFFECTS OF TEMPERATURE AND SALINITY ON THE METABOLIC RATE OF JUVENILE MAC~OB~AC~~U~ ~O~E~~~~G~~ (CRUSTACEA: PALAEMONIDAE) S.G.
NELSON’,
D. A. ARMSTRONG’,A. W. KNIGHT” AND H. W. LI’ University of California, Davis, CA 95616, U.S.A. (Received 27 July 1976)
Abstract-l. The respiration of juvenile Macrobrachium rosenbergii were monitored in response to combinations of temperature and salinity encompassing temperatures of 20, 27 and 34°C and salinities of 0. 7, 14, 20 and 287&,. 2. Both oxygen consumption rate and QO, were influenced by the body weight of the individual prawns. 3. Metabolic rates were determined to be infiuenced by temperature and salinity and the temperaturesalinity interaction. 4. The Qio values for metabolic rate were influenced by the temperature range considered but there was no obvious response of Qio to salinity. 5. The metabolic responses to temperature and salinity may determine the distribution and migration of the species in natural habitats.
INTRODUCTION
The rate of metabolism of invertebrates is influenced by a wide variety of environmental stimuli. It is the nature of these physiological responses to environmental factors which will dete~ine the biological fitness of individuals of a population and which will ultimately define the distributional limits of the species. The collective environmental limits imposed by these responses determine the fundamental niche of an organism, while the interactions of environmental and biotic. factors circumscribe the N-dimensional realized niche as defined by Hutchinson (1958). Examination of the physiological responses of individuals to specific environmental regimes allows the delineation of causal relationships underlying the distribution of a species (Fry, 1947). in aquatic ecosystems, temperature and salinity are generally considered to be the major environmental properties which limit the dist~bution of invertebrates (Kinne, 1971). These two environmental properties are suspected of being the major factors limiting the distribution of populations of Macrobrachim rosenbergii (George, 1969). M. rosenbergii is a large prawn of the family Palaemonidae indigenous to tropical fresh and brackish water habitats of the Indo-Pacific (Johnson, 1967; George, 1969). Other species of the genus are found in tropical and subtropical areas around the globe (Hedgepeth, 1948; Williams, 1965). M. rosenbergii is found in habitats of about 25°C in Malaya (Johnson, 1967) and from 27 to 34°C in India (John, 1957; Rao, 1967). The species inhabits a wide range of environmen~l salinities during its life cycle and is found in waters ranging
from 0 to 18%,. During the reproductive season adults migrate from freshwater habitats to estuarine regions where the eggs hatch and where the planktonic larval development occurs. After settling, the juvenile prawns migrate back into freshwater habitats presumably in response to environmental cues (John, 1957; Raman. 1967; George, 1969). Very little information is available regarding the physiological responses of this species to environmental conditions even though it is a species of commercial interest as an item of fisheries exploitation in its native habitats (Holthius & Rosa, 1965; Raman, 1967) as well as an increasingly important aquaculture organism around the world (Ling, 1962, 1969; Fujimura & Okamota, 1970; Provenzano, 1973). This study examines the rate of metabolism of juvenile M. rosenbergii in response to a variety of temperature and salinity combinations. The results are discussed relative to the distributional and migratory behavioral patterns of the species in the field. METHODS AND MATERIALS
Juvenile M. rosenbergii were reared at the University of California, Davis, from stock initially supplied by S. A. SerITing of Encinitas, CA. Prior to the experiment, prawns were mass held in fresh water in 4001. piywood tanks. Water with a pH of 7.8 was aerated and circulated through gravel and charcoal filters for purification. The water temperature was maintained at 24 k 1°C using immersion heaters with thermoregulators. A photoperiod of 15 hr light and 8 hr dark was maintained during the holding period. For a~limati~ation to experimental conditions, juvenile prawns were placed in groups of 30 in 201. all-glass aquaria. The aquaria were aerated through substrate filters covered with a 2.5 cm layer of washed gravel. All aquaria i Department of Land, Air and Water Resources, Water were positioned in large constant temperature (+O.YC) Science and Engineering Section. water baths equipped with 750 W heaters and/or cooling * Department of Animal Physiology. units. 533
Acclimatization began with prawns of all groups held in fresh water (o”,,,,) at 24 f O.S’C. Temperatures were then changed at the rate of 3 C~day until the desired temperatures of 20. 27. and 34’C were reached. Salinities in all aquaria, except that left at O”,,,,, were increased 4”,,,,:day by the addition of artificial sea salts (Instant Ocean) until the experimental salinities of 0. 7. 14, ?I and 2X”,,,, were ohtained. Animals were fed Purina Ration No. 20 and tubifecid worms during the period required for temperature,!salinity change. but were starved 24 hr prior to a respirometry run. The dry weights of the 333 experimental animals used in these tests ranged from 0.02 to 0.25 g with a mean weight of 0. I I g. After 48 hr of acclimation at each of the 15 experimental temperatureesalinity combinations, the prawns were subsampled and 24 prawns removed from each group. These individuals were used for monitoring metabolic rates. Oxygen consumption was measured using a Gilson 20 channel respirometer. Each animal was placed in a 125 ml respirometry flask which contained 75 ml of water at the appropriate temperature-salinity combination. The side arm of each flask contained a strip of filter paper saturated with 0.3 ml of 0.2M KOH solution to absorb COZ. Two control flasks were prepared in the same manner and placed at opposite ends of the respirometer. These were sensitive to general changes in air temperature and pressure. and were used to correct the readings from experimental flasks.
The flasks were agitated at 84 oscillations:mm to insure aeration of the water. The prawns were acclimated to the respirometer flasks for 30 min prior to initiation of oxygen consumption monitoring. Oxygen consumption readings were taken every 10 min for 30 min. The respirometer was then opened for 30min to allow aeration or equilibration of the water in the flasks. Then oxygen consumption was again measured at IO-min intervals for a final 3O-min period. The animals were removed from the flasks, killed by brief immersion in boiling water. oven dried at 104“C overnight. cooled in a desiccator to room temperature (23’C) and weighed to the 0.01 g on a Mettler electronic balance. Oxygen consumption rates for each individual were determined by fitting a regression line by the method of
Table
I. Regression
statistics
the least squares to the i-egresston ot ml of oxygen COW sumed with time. The slope of the htrc indicated the rate of oxygen consumption in ml OL min. For each individual, the rates for the two 30-min monitoring periods wcrc averaged and the mean value used to indicate the oxygen con sumption rate of the individual as ml Or consumed hr. By dividing by the dry weight of the organism these values were then converted to ml 0, consumed g dry weight hr (QOz). Regression analysis (Snedccor & C‘ochran. I9671 was performed for each group of prawns to detcrminc the effects of individual dry weight on the metabolic rate expressed as ml of OL consumedhr and as ml of OL consumed:hr/g dry weight. Also the data were statistically analyzed by two-way analysis of variance (Snedecor &r Cochran. 1967) to determine if respiration was significantly influenced by either salinity or temperature and to determme if there was any interaction between these two factors
RESI
Oxygen consumption per individual in all temperature--salinity combinations was influenced by the weight of the organism. The equation which best described this relation was found to be: Log y = Log Y + /r Log (0. where y = ml of oxygen consumed.hr. and (1) = dry weight of the organism in g. ‘A= the y intercept and /I = the slope. This model was used to compute the regressions of Log y on Log w for each temperaturesalinity combination. The r values for each regression line ranged from 0.5651 to 0.9265 as shown in Table I. The correlation coefficients for all groups except one were significant at the I”;, level of significance (Snedecor & Cochran, 1967). indicating a strong relationship between oxygen consumption per individual and weight. The one exception was the group at 20°C and 28”,,,, which may be the result of severe salinity stress coupled with lower thermal stress. The
for the relationship between metabolic Mucrohrcrchiutn rosenhrrqii Regression
Temperature
( Cl 20 20 20 20 20
Salinity
(“J
N
0
24 24 24 24 I6 23 24 23 24 16 ‘3 24 24 24 I5
7 14 ‘0 2x 0 7 14 20 28 0 7 I4 20 28
37 _I
27 ‘7 27 27 34 34 34 34 35 t indicates * indicates
a significant a significant
log oxygen consumption (ml/hr) on log dry weight (g) correlation coefficient (r)? 0.8013411 0.871070t 0.8 13075t 0.736377t
0.097899 0.744106t 0.X7766310.63oOX4t 0.608630+ ().X72459+ 0.841 152i 0.7 10X7+ ().5651X+ 0.926536t 0.89455ot correlation correlation
LTS
rate and dry weight
of luvenilr
Statistics
slope
Q02 (ml O,,g;hrl on dry weight (g) correlation coefficient (r)
slope
0.6406 0.8219 0.7376 I .3847 0. I458 0.5430 0.8577 0.3861 0.6775 (1.7453 0.6222 0.6658 0.6347 1.1130 0.8605
-0.6l1807* -0.310416 - 0.499493* 0.095845 - 0.55680 I * 0.I97425 ~ 0.29 I I93 -(X555941* -0.301960 -0.51x879* ~ 0.639260* - 0.55 1660* - 0.317224* ~ 0305x37 -0.361x23
- 0.0037 - 0.00 I 2 - 0.02 I + 0.0056 - o.GO47 +0.0014 ~ 0.0029 - 0.0083 -0.0019 - 0.0026 -0.012x -0.0093 - 0.0050 -- 0.0003 -0.001x
at the I”,> level of significance. at the 5”,, level of signiticancc
535
The effects of temperature and salinity plots are also indicated in Table 1 and range from 0.1458 to 1.3847. When expressed on a per gram basis the metabolic rate (QO,) relationship with weight changes. This relationship is also shown in Table 1. The correlation coefficients for the relationship between QO, and weight ranged from 0.0959 to 0.6393. Within the 1.5 experimental groups, 8 showed a significant relationship with weight while the 7 others were not significant at the 5% level of significance. This indicates that there is a slight negative correlation between QO, and weight. The slopes ranged from -0.0128 to +0.0056. Because of these low values for the regression line slopes and the limited weight range used in the study the effects of weight on metabolism can be considered negligible when expressed on a per gram basis. The mean metabolic rate (QO,) of the juvenile prawns ranged from 3.15 ml O,/g/hr at 34°C and Oo&, to 0.61 ml O,/g/hr at 20 and 28°C. The results of the two-way analysis of variance (Snedecor & Cochran, 1967) are shown in Table 2. The F values for the variation in QO, due to temperature (F = 16.723), salinity (F = 19.128), and the interaction between temperature and salinity (F = 6.360) indicated a significant effect due to each of these components of the analysis (P < 0.01 in each case). The mean metabolic rate at each temperaturesalinity combination is displayed in Fig. 1 along with the standard deviations. Metabolic rates at 20°C are fairly constant between salinities except at 28”/, when a sharp decline is noted. At 27°C the decline in metabolic rate occurs at salinities of 20%, or greater. Metabolic rates are more severely depressed at higher salinities. At 34°C the respiratory rate declines with any increase in salinity. At all temperatures, the prawns at 28?&,were sluggish and slow to right themselves indicating the severity of the stress at this high salinity. The responses of metabolic rates to temperature were expressed as QIo values according to the formula: slope of the log-log
where K, = the metabolic rate at temperature tI K, = the metabolic rate at temperature t2 The QIo value for the prawns was determined at each salinity for the temperature ranges from 20 to 27°C and from 27 to 34°C. The QIo values were larger for the temperature range from 20 to 27°C than for the temperature range from 27 to 34°C at all salinities
Table 2. Analysis of variance demonstrating the effects of temperature and salinity on the metabolic rate (ml 0,&/g) of juvenile kfacrohrnchium rosenbergii
Source Temperature Salinity Interaction Error
Degrees of freedom 2 4 8 317
Sum of Squares
Mean Square
F
107.8517 53.9259 163.723-i 19.12W 25.2010 6.3003 6.360t 16.7575 2.0947 104.4113 0.3294
tall F values are significant at the 1% level of significance.
0.0 0
14
7
SALINITY
20
28
(parts per thousand 1
Fig. 1. Mean metabolic rates (fS.E.)
of juvenile Macroof temperature and salinity.
brachium rosenbergii in response to combinations
(Fig. 2). There was no obvious trend for the relationship between QIo and salinity. DISCUSSION
Many authors have investigated the response of metabolic rates to combinations of temperature and salinity for a variety of crustacean species (see Lockwood, 1967; Kinne, 1971 for reviews). Several authors have suggested that increased metabolic rates at salinities differing from the iso-osmotic point as indicative of the increased energy-cost due to osmoregulation (see Beadle, 1931; Lofts, 1956; Dehnel & McCaughran, 1964; Kutty et al., 1971). The credence of these interpretations have been somewhat diminished by numerous reports for other species which indicate either a decrease in metabolic rate in supra and/or subnormal salinities (see Simmons & Knight, 1975; Dimock & Groves, 1975) or no correlation between metabolic rate and salinity (Elfringhan, 1965; McFarland & Pickens, 1965). This variability in the response in a variety of species has led to difficulty in interpreting results of environmental changes on metabolic rate as pointed out in the review by Lockwood (1967).
4
120-27OC
3
I
0
0
7
14 SALINITY
20
28
(&I
Fig. 2. Qlo values for the response of the metabolic rate (QO,) to two temperature ranges at each of 5 salinities.
In Mucrohruchiurrz roserhrrgii the iso-osmotic point was reported to be about 18”<,,,(Sandifer ef nl.. 1975). Our results do not indicate a decrease in metabolic rate associated with this salinity at any experimental temperature. Therefore. we concluded that the metabolic work due to osmoregulation was not a significant contributing factor in determining the metabolic rates observed in this study. The nature of the observed response of metabolic rate at all temperatures was depression of oxygen consumption with increasing salinity past a critical point. This critical sajinity point was different for each temperature studied and in general decreased with increasing temperature. At the highest salinities (X”,,,) behavioral observations of the prawns justify interpreting the observed depression of a metabolic rate as indications of a rather severe environmental stress. Therefore. decreases in metabolic rate at lower salinities at which behavior was not drastically altered may also be interpreted as some degree of stress or interference with the processes of metabolism. The metabolic rate depression due to salinity was much more pronounced at higher temperatures. It is possible that this indicates a failure or hindrance of osmoregulatory mechanisms at high temperatures or decreased efficiency of enzyme systems involved in osmorgulation beyond an optimum thermal range. Even though metabolic rates were influenced by salinity the response of metabolic rate to temperature seemed unaltered by salinity (Fig. 2). The Qlo values were lower for the higher temperature range examined (27 34’C). This pattern of thermal insensitivity of metabolic rate in the active temperature range has also been reported for other crustaceans (Vernberg. 1959). It appears that metabolic depression due to salinity stress does not affect the response to temperature even though the response of metabolism to salinity is altered by temperature. The interpretation of osmoregulatory stress at high temperatures is supported by field observations of the biology of the species in the wild. Detailed studies on the biology and behavior of the prawn in native habitats are few. however available reports serve to provide an ecological context for interpretation of the metabolic responses to environmental conditions. In India. the larval prawns develop in estuaries where salinities range from 5 to 2@‘<,,,(George, 1969). Migration of juveniles into the deeper channels of freshwater streams occurs during the dry season and the young prawns move back into the ostuary during the occasional rains during this season (Raman, 1967). George (1969) reports juveniles and adults near the mouth of rivers at 18’:,,, which suggests that salinity alone does not trigger the upstream migrations. John (1957) has suggested that temperature may be the environmental cue for movements into and out of the back water. Rains which reduce either the salinity or the temperature of the back water allow the prawns to reenter these areas. Johnson (1967) in his study of the distribution of freshwater prawns in Malaya notes that ~ucrobrue~liu~ ~os~~lb~r~jj is not found in high temperature habitats. and indicates that the temperature range inhabited by hf. rmscdwrgii in Malaya to be 34.5 25.1 C. The situation in India is apparently different as John (1957) indicates optimum activity of populations of ‘n/l. mscdxvyii occurs at tempera-
tures of 29%34 C in that country. The data from the present study indicate that the movements into and out of the estuaries may be initiated due to metabolic stress resulting from the interaction of environmental temperature and salinity. Also this metabolic stress maq limit the distribution of the species to waters below 34 C. We have demonstrated that some components of an organism’s niche can be delineated by a study of physiological responses to environmental conditions. Such studies can aid in understanding aspects of the distribution and behavior of a species however. illterprct~~tion of physiolo~cal responses are difficult without an (I priori knowledge of the organism’s biology to provide an ecological context for such interpretations. -lckrto~~/rd~~rrrt~~~~~.s This tnvestigatton was funded in part hq a special appropriation of the California State Legislature and by the University of California Agricultural Experiment Station. The authors are indebted to Mary Ann Simmons for her help throughout the project. REFERENCES
C. (1931)The effect of saiinit!
BEADLI:L.
water content and respiration J. uxp. Bioi. 8. :!I 1-227. DI+~NFI. P.
of marme
changes on the invertebrates.
MCCA~CZ~KAU D. A. (1964) Gill tissue in two species of estuarme crabs. Camp. Binc/WI. Physiol. 13. 233 -259. IXM~CIC R. V. & GROVESK. H. (1975) Interaction of temperature and salinity on oxygen consumption of the estuarine crab Purropeus horhorfi. Mm. Bid. 33, 301 -308. EL~R~NGHAM S. K. (1965) The respiration of ~i~i~~ri~ [Isopoda] in relation to salinity. J. 8A,Iar. Him/. Axsoc. [:.I<. 45, 145-152. FRY F. E. J. (1947) Effects of the environment on animal activity. Univ. yf 7’oronto Sm. Bid 5.5 (Puhl. Orltario Fish Res. Lab.) 68, L61.
A. &
respiration
HIWXX?~T~~J. W. (194X) The North Amcrxan Species of ?,~acrc)htcifkittnr (River shrimp). T<,Yu.sJ. Scirncr. 28 3X. HOLTHWS L. B. & ROSA H. JK. (1965) List of species of
shrimps
and prawns
of economic
value. F‘AO Fish Tech.
Pap. 52, ?1 pp. HUTCHINSONG. E. (19%)
Concluding remarks. Cold Marhoi Symp. quunt. Rio/. 22. 415417.
JOHN M. C. (1957) Bionomics
and life-historv
Spring
of Mncrohra-
JOHNSOND. S. (1967) Some factors influencing the distribution of freshwater prawns in Malaya. Pror.. Sytxp. Crustucerr Mar. Bid. Assoc. India I, 41X--433. KINNI- 0. (1971) Salinity: invertebrates. In Marirw Eroloqy (Edited by KINNE0.) Vol. 1, Part 2. pp, XZl~-995. Wiley-
Interscience, New York. Kt:~u M. N.. M~~RWAPOOPATW G. & KRISI~NANT. S. (1971) Influence of salinity and t~mperatl~re on the oxygen consumption in young juvcnilcs of the Indian prawn Pcnueus i&icus. Mrrr. Rid. I I, 125. 13 I. LING S. W. (1967) Studies on the rearing of larvae and juveniles and culturing of adults of Mucrohruchiun~ rosdwyii (DeMan), Imk-Pucific F‘isll. Courlc. CurrerIt .G%rs Hltlt. 3s. I 1I
The effects of temperature and salinity LING S. W. (1969) Methods of rearing and culturing MacFAO Rep. 57, 607419. L~XKWO~DA. P. M. (1967) Aspects of the Physiology Crustacea. W. H. Freeman & Co. 328 pp. robrachium
rosenbergii.
of
LOFTSB. (1956) The effects of salinity changes on the respiratory rate of the prawn Paiaemone~es varians (Leach). J. exp. Biof. 33, 730-736.
MCFARLANDW. N. & PICKENS P. E. (1965) The effects of season, temperature, and salinity on standard and active oxygen consumption of the grass shrimp Palaamonetes vulgaris (Sayre). Can. J. Zool. 43. 571-585. PROVENZANO A. J. JR. (1973) Some results of a pilot project on freshwater prawn culture in Jamaica. Proc. World Maricul~ure Sot. 4, 57-61.
RAMANK. (1967) Observations on the fishery and biology of the giant freshwater prawn Macrobrachium rosenbergii deMan. Proc. Symp. Crustacea, Mar. Biol. Assoc. India, Part II. 649-669. RAO R. M. (1967) Studies on the biology of Macrobrachium
c B.P. S6!4@-F
rosenhergii
537
(de Man) of the Hooghly estuary with notes on its fishery. Proc. Nat. Inst. Sci. India 33(5 & 6), 252-279. . SANDIFERP. A., HOPKINSJ. S. & SMITHT. I. J. (1975) Observations on salinity tolerance and osmoregulation in laboratory-r~red Mu~robracbi~ rosenbergii postlarvae (Crustacea: Caridea). Aquuculfure 6, 103-t 14. SIMMONS M. A. & KNIGHT A. W. (1975) Respiratory response of Neomysis intermedia (Crustacea:Mysidacea) to changes in salinity, temperature and season. Comp. Biothem. Physiol. SOA, 181-193. SNEDECORG. W. & COCHRANW. G. (1967) Statistical .~e~h~s. Iowa State Univ. Press, Ames, Iowa. 539 DD. VERNBERG F. J. (1959) Studies on the physiological v&iation between tropical and temperate zone fiddler crabs of the genus Uca. II. Oxygen consumption of whole organisms. Biol. Bull. 117, 163-184. WILLIAMSA. B. (1965) Marine decapod crustaceans of the Carolinas. Fish. Bull. 65, l-298.
NELSON’,
D. A. ARMSTRONG’,A. W. KNIGHT” AND H. W. LI’ University of California, Davis, CA 95616, U.S.A. (Received 27 July 1976)
Abstract-l. The respiration of juvenile Macrobrachium rosenbergii were monitored in response to combinations of temperature and salinity encompassing temperatures of 20, 27 and 34°C and salinities of 0. 7, 14, 20 and 287&,. 2. Both oxygen consumption rate and QO, were influenced by the body weight of the individual prawns. 3. Metabolic rates were determined to be infiuenced by temperature and salinity and the temperaturesalinity interaction. 4. The Qio values for metabolic rate were influenced by the temperature range considered but there was no obvious response of Qio to salinity. 5. The metabolic responses to temperature and salinity may determine the distribution and migration of the species in natural habitats.
INTRODUCTION
The rate of metabolism of invertebrates is influenced by a wide variety of environmental stimuli. It is the nature of these physiological responses to environmental factors which will dete~ine the biological fitness of individuals of a population and which will ultimately define the distributional limits of the species. The collective environmental limits imposed by these responses determine the fundamental niche of an organism, while the interactions of environmental and biotic. factors circumscribe the N-dimensional realized niche as defined by Hutchinson (1958). Examination of the physiological responses of individuals to specific environmental regimes allows the delineation of causal relationships underlying the distribution of a species (Fry, 1947). in aquatic ecosystems, temperature and salinity are generally considered to be the major environmental properties which limit the dist~bution of invertebrates (Kinne, 1971). These two environmental properties are suspected of being the major factors limiting the distribution of populations of Macrobrachim rosenbergii (George, 1969). M. rosenbergii is a large prawn of the family Palaemonidae indigenous to tropical fresh and brackish water habitats of the Indo-Pacific (Johnson, 1967; George, 1969). Other species of the genus are found in tropical and subtropical areas around the globe (Hedgepeth, 1948; Williams, 1965). M. rosenbergii is found in habitats of about 25°C in Malaya (Johnson, 1967) and from 27 to 34°C in India (John, 1957; Rao, 1967). The species inhabits a wide range of environmen~l salinities during its life cycle and is found in waters ranging
from 0 to 18%,. During the reproductive season adults migrate from freshwater habitats to estuarine regions where the eggs hatch and where the planktonic larval development occurs. After settling, the juvenile prawns migrate back into freshwater habitats presumably in response to environmental cues (John, 1957; Raman. 1967; George, 1969). Very little information is available regarding the physiological responses of this species to environmental conditions even though it is a species of commercial interest as an item of fisheries exploitation in its native habitats (Holthius & Rosa, 1965; Raman, 1967) as well as an increasingly important aquaculture organism around the world (Ling, 1962, 1969; Fujimura & Okamota, 1970; Provenzano, 1973). This study examines the rate of metabolism of juvenile M. rosenbergii in response to a variety of temperature and salinity combinations. The results are discussed relative to the distributional and migratory behavioral patterns of the species in the field. METHODS AND MATERIALS
Juvenile M. rosenbergii were reared at the University of California, Davis, from stock initially supplied by S. A. SerITing of Encinitas, CA. Prior to the experiment, prawns were mass held in fresh water in 4001. piywood tanks. Water with a pH of 7.8 was aerated and circulated through gravel and charcoal filters for purification. The water temperature was maintained at 24 k 1°C using immersion heaters with thermoregulators. A photoperiod of 15 hr light and 8 hr dark was maintained during the holding period. For a~limati~ation to experimental conditions, juvenile prawns were placed in groups of 30 in 201. all-glass aquaria. The aquaria were aerated through substrate filters covered with a 2.5 cm layer of washed gravel. All aquaria i Department of Land, Air and Water Resources, Water were positioned in large constant temperature (+O.YC) Science and Engineering Section. water baths equipped with 750 W heaters and/or cooling * Department of Animal Physiology. units. 533
Acclimatization began with prawns of all groups held in fresh water (o”,,,,) at 24 f O.S’C. Temperatures were then changed at the rate of 3 C~day until the desired temperatures of 20. 27. and 34’C were reached. Salinities in all aquaria, except that left at O”,,,,, were increased 4”,,,,:day by the addition of artificial sea salts (Instant Ocean) until the experimental salinities of 0. 7. 14, ?I and 2X”,,,, were ohtained. Animals were fed Purina Ration No. 20 and tubifecid worms during the period required for temperature,!salinity change. but were starved 24 hr prior to a respirometry run. The dry weights of the 333 experimental animals used in these tests ranged from 0.02 to 0.25 g with a mean weight of 0. I I g. After 48 hr of acclimation at each of the 15 experimental temperatureesalinity combinations, the prawns were subsampled and 24 prawns removed from each group. These individuals were used for monitoring metabolic rates. Oxygen consumption was measured using a Gilson 20 channel respirometer. Each animal was placed in a 125 ml respirometry flask which contained 75 ml of water at the appropriate temperature-salinity combination. The side arm of each flask contained a strip of filter paper saturated with 0.3 ml of 0.2M KOH solution to absorb COZ. Two control flasks were prepared in the same manner and placed at opposite ends of the respirometer. These were sensitive to general changes in air temperature and pressure. and were used to correct the readings from experimental flasks.
The flasks were agitated at 84 oscillations:mm to insure aeration of the water. The prawns were acclimated to the respirometer flasks for 30 min prior to initiation of oxygen consumption monitoring. Oxygen consumption readings were taken every 10 min for 30 min. The respirometer was then opened for 30min to allow aeration or equilibration of the water in the flasks. Then oxygen consumption was again measured at IO-min intervals for a final 3O-min period. The animals were removed from the flasks, killed by brief immersion in boiling water. oven dried at 104“C overnight. cooled in a desiccator to room temperature (23’C) and weighed to the 0.01 g on a Mettler electronic balance. Oxygen consumption rates for each individual were determined by fitting a regression line by the method of
Table
I. Regression
statistics
the least squares to the i-egresston ot ml of oxygen COW sumed with time. The slope of the htrc indicated the rate of oxygen consumption in ml OL min. For each individual, the rates for the two 30-min monitoring periods wcrc averaged and the mean value used to indicate the oxygen con sumption rate of the individual as ml Or consumed hr. By dividing by the dry weight of the organism these values were then converted to ml 0, consumed g dry weight hr (QOz). Regression analysis (Snedccor & C‘ochran. I9671 was performed for each group of prawns to detcrminc the effects of individual dry weight on the metabolic rate expressed as ml of OL consumedhr and as ml of OL consumed:hr/g dry weight. Also the data were statistically analyzed by two-way analysis of variance (Snedecor &r Cochran. 1967) to determine if respiration was significantly influenced by either salinity or temperature and to determme if there was any interaction between these two factors
RESI
Oxygen consumption per individual in all temperature--salinity combinations was influenced by the weight of the organism. The equation which best described this relation was found to be: Log y = Log Y + /r Log (0. where y = ml of oxygen consumed.hr. and (1) = dry weight of the organism in g. ‘A= the y intercept and /I = the slope. This model was used to compute the regressions of Log y on Log w for each temperaturesalinity combination. The r values for each regression line ranged from 0.5651 to 0.9265 as shown in Table I. The correlation coefficients for all groups except one were significant at the I”;, level of significance (Snedecor & Cochran, 1967). indicating a strong relationship between oxygen consumption per individual and weight. The one exception was the group at 20°C and 28”,,,, which may be the result of severe salinity stress coupled with lower thermal stress. The
for the relationship between metabolic Mucrohrcrchiutn rosenhrrqii Regression
Temperature
( Cl 20 20 20 20 20
Salinity
(“J
N
0
24 24 24 24 I6 23 24 23 24 16 ‘3 24 24 24 I5
7 14 ‘0 2x 0 7 14 20 28 0 7 I4 20 28
37 _I
27 ‘7 27 27 34 34 34 34 35 t indicates * indicates
a significant a significant
log oxygen consumption (ml/hr) on log dry weight (g) correlation coefficient (r)? 0.8013411 0.871070t 0.8 13075t 0.736377t
0.097899 0.744106t 0.X7766310.63oOX4t 0.608630+ ().X72459+ 0.841 152i 0.7 10X7+ ().5651X+ 0.926536t 0.89455ot correlation correlation
LTS
rate and dry weight
of luvenilr
Statistics
slope
Q02 (ml O,,g;hrl on dry weight (g) correlation coefficient (r)
slope
0.6406 0.8219 0.7376 I .3847 0. I458 0.5430 0.8577 0.3861 0.6775 (1.7453 0.6222 0.6658 0.6347 1.1130 0.8605
-0.6l1807* -0.310416 - 0.499493* 0.095845 - 0.55680 I * 0.I97425 ~ 0.29 I I93 -(X555941* -0.301960 -0.51x879* ~ 0.639260* - 0.55 1660* - 0.317224* ~ 0305x37 -0.361x23
- 0.0037 - 0.00 I 2 - 0.02 I + 0.0056 - o.GO47 +0.0014 ~ 0.0029 - 0.0083 -0.0019 - 0.0026 -0.012x -0.0093 - 0.0050 -- 0.0003 -0.001x
at the I”,> level of significance. at the 5”,, level of signiticancc
535
The effects of temperature and salinity plots are also indicated in Table 1 and range from 0.1458 to 1.3847. When expressed on a per gram basis the metabolic rate (QO,) relationship with weight changes. This relationship is also shown in Table 1. The correlation coefficients for the relationship between QO, and weight ranged from 0.0959 to 0.6393. Within the 1.5 experimental groups, 8 showed a significant relationship with weight while the 7 others were not significant at the 5% level of significance. This indicates that there is a slight negative correlation between QO, and weight. The slopes ranged from -0.0128 to +0.0056. Because of these low values for the regression line slopes and the limited weight range used in the study the effects of weight on metabolism can be considered negligible when expressed on a per gram basis. The mean metabolic rate (QO,) of the juvenile prawns ranged from 3.15 ml O,/g/hr at 34°C and Oo&, to 0.61 ml O,/g/hr at 20 and 28°C. The results of the two-way analysis of variance (Snedecor & Cochran, 1967) are shown in Table 2. The F values for the variation in QO, due to temperature (F = 16.723), salinity (F = 19.128), and the interaction between temperature and salinity (F = 6.360) indicated a significant effect due to each of these components of the analysis (P < 0.01 in each case). The mean metabolic rate at each temperaturesalinity combination is displayed in Fig. 1 along with the standard deviations. Metabolic rates at 20°C are fairly constant between salinities except at 28”/, when a sharp decline is noted. At 27°C the decline in metabolic rate occurs at salinities of 20%, or greater. Metabolic rates are more severely depressed at higher salinities. At 34°C the respiratory rate declines with any increase in salinity. At all temperatures, the prawns at 28?&,were sluggish and slow to right themselves indicating the severity of the stress at this high salinity. The responses of metabolic rates to temperature were expressed as QIo values according to the formula: slope of the log-log
where K, = the metabolic rate at temperature tI K, = the metabolic rate at temperature t2 The QIo value for the prawns was determined at each salinity for the temperature ranges from 20 to 27°C and from 27 to 34°C. The QIo values were larger for the temperature range from 20 to 27°C than for the temperature range from 27 to 34°C at all salinities
Table 2. Analysis of variance demonstrating the effects of temperature and salinity on the metabolic rate (ml 0,&/g) of juvenile kfacrohrnchium rosenbergii
Source Temperature Salinity Interaction Error
Degrees of freedom 2 4 8 317
Sum of Squares
Mean Square
F
107.8517 53.9259 163.723-i 19.12W 25.2010 6.3003 6.360t 16.7575 2.0947 104.4113 0.3294
tall F values are significant at the 1% level of significance.
0.0 0
14
7
SALINITY
20
28
(parts per thousand 1
Fig. 1. Mean metabolic rates (fS.E.)
of juvenile Macroof temperature and salinity.
brachium rosenbergii in response to combinations
(Fig. 2). There was no obvious trend for the relationship between QIo and salinity. DISCUSSION
Many authors have investigated the response of metabolic rates to combinations of temperature and salinity for a variety of crustacean species (see Lockwood, 1967; Kinne, 1971 for reviews). Several authors have suggested that increased metabolic rates at salinities differing from the iso-osmotic point as indicative of the increased energy-cost due to osmoregulation (see Beadle, 1931; Lofts, 1956; Dehnel & McCaughran, 1964; Kutty et al., 1971). The credence of these interpretations have been somewhat diminished by numerous reports for other species which indicate either a decrease in metabolic rate in supra and/or subnormal salinities (see Simmons & Knight, 1975; Dimock & Groves, 1975) or no correlation between metabolic rate and salinity (Elfringhan, 1965; McFarland & Pickens, 1965). This variability in the response in a variety of species has led to difficulty in interpreting results of environmental changes on metabolic rate as pointed out in the review by Lockwood (1967).
4
120-27OC
3
I
0
0
7
14 SALINITY
20
28
(&I
Fig. 2. Qlo values for the response of the metabolic rate (QO,) to two temperature ranges at each of 5 salinities.
In Mucrohruchiurrz roserhrrgii the iso-osmotic point was reported to be about 18”<,,,(Sandifer ef nl.. 1975). Our results do not indicate a decrease in metabolic rate associated with this salinity at any experimental temperature. Therefore. we concluded that the metabolic work due to osmoregulation was not a significant contributing factor in determining the metabolic rates observed in this study. The nature of the observed response of metabolic rate at all temperatures was depression of oxygen consumption with increasing salinity past a critical point. This critical sajinity point was different for each temperature studied and in general decreased with increasing temperature. At the highest salinities (X”,,,) behavioral observations of the prawns justify interpreting the observed depression of a metabolic rate as indications of a rather severe environmental stress. Therefore. decreases in metabolic rate at lower salinities at which behavior was not drastically altered may also be interpreted as some degree of stress or interference with the processes of metabolism. The metabolic rate depression due to salinity was much more pronounced at higher temperatures. It is possible that this indicates a failure or hindrance of osmoregulatory mechanisms at high temperatures or decreased efficiency of enzyme systems involved in osmorgulation beyond an optimum thermal range. Even though metabolic rates were influenced by salinity the response of metabolic rate to temperature seemed unaltered by salinity (Fig. 2). The Qlo values were lower for the higher temperature range examined (27 34’C). This pattern of thermal insensitivity of metabolic rate in the active temperature range has also been reported for other crustaceans (Vernberg. 1959). It appears that metabolic depression due to salinity stress does not affect the response to temperature even though the response of metabolism to salinity is altered by temperature. The interpretation of osmoregulatory stress at high temperatures is supported by field observations of the biology of the species in the wild. Detailed studies on the biology and behavior of the prawn in native habitats are few. however available reports serve to provide an ecological context for interpretation of the metabolic responses to environmental conditions. In India. the larval prawns develop in estuaries where salinities range from 5 to 2@‘<,,,(George, 1969). Migration of juveniles into the deeper channels of freshwater streams occurs during the dry season and the young prawns move back into the ostuary during the occasional rains during this season (Raman, 1967). George (1969) reports juveniles and adults near the mouth of rivers at 18’:,,, which suggests that salinity alone does not trigger the upstream migrations. John (1957) has suggested that temperature may be the environmental cue for movements into and out of the back water. Rains which reduce either the salinity or the temperature of the back water allow the prawns to reenter these areas. Johnson (1967) in his study of the distribution of freshwater prawns in Malaya notes that ~ucrobrue~liu~ ~os~~lb~r~jj is not found in high temperature habitats. and indicates that the temperature range inhabited by hf. rmscdwrgii in Malaya to be 34.5 25.1 C. The situation in India is apparently different as John (1957) indicates optimum activity of populations of ‘n/l. mscdxvyii occurs at tempera-
tures of 29%34 C in that country. The data from the present study indicate that the movements into and out of the estuaries may be initiated due to metabolic stress resulting from the interaction of environmental temperature and salinity. Also this metabolic stress maq limit the distribution of the species to waters below 34 C. We have demonstrated that some components of an organism’s niche can be delineated by a study of physiological responses to environmental conditions. Such studies can aid in understanding aspects of the distribution and behavior of a species however. illterprct~~tion of physiolo~cal responses are difficult without an (I priori knowledge of the organism’s biology to provide an ecological context for such interpretations. -lckrto~~/rd~~rrrt~~~~~.s This tnvestigatton was funded in part hq a special appropriation of the California State Legislature and by the University of California Agricultural Experiment Station. The authors are indebted to Mary Ann Simmons for her help throughout the project. REFERENCES
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