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The effect of temperature and salinity on oxygen consumption of post-larvae of Macrobrachium rosenbergii (de man) (crustacea: palaemonidae)
THE EFFECT OF TEMPERATURE AND SALINITY ON OXYGEN CONSUMPTION OF POST-LARVAE OF MACROBRACHIUM RUSENBERGII (DE MAN) (CRUSTACEA: PALAEMONIDAE) MARIAN J. STEPHENSONand ALLEN W. KNIGHT Department of Land, Air and Water Resources, University of California, Davis, CA 95616, U.S.A. (Received 10 March 1980) Abstract-l. Oxygen consumption of post-larvae of the catadromous prawn Macrohrachiunl rosenhergii was monitored at 20, 27, and 34 C at four levels of salinity (0, 7. 14, and 28’:,,,)using a Gilson differential
respirometer. 2. Differences in oxygen consumption among salinity treatments were not significant except in larger animals, in which oxygen consumption decreased as salinity increased. 3. Oxygen consumption increased with temperature. There was some evidence of weight dependency of the temperature response. Deviations in the weight-respiration relation at 34°C suggest high temperature is stressful. 4. These data suggest that salinity does not affect distribution of small post-larvae but may influence movements of larger animals. High temperatures may induce migrations of smaller post-larvae.
INTRODUCTION Macrobrachium rosenbergii (De Man), a giant prawn native to the Indo-Pacific region, is an active migrator between brackish and freshwater habitats. Females migrate to estuaries or brackish backwaters for the hatching of eggs; it has been demonstrated in the laboratory that brackish water is required for larval survival (Ling & Merican, 1961). Following metamorphosis, the semi-planktonic post-larvae move upstream to take up a more sedentary existence in freshwater. Changes in temperature and salinity associated with seasonal weather patterns have been suggested as stimulants for this migration (John, 1957). However, few studies have been conducted of crustacean responses to salinity and temperature during life stages associated with active migration (ZeinEtdin, 1963; Zein-Eldin & Aldrich, 1965; &in-Eldin & Griffith, 1966; Sandifer et al., 1975; Richard, 1978). While a relationship is recognized between the osmoregulatory patterns of estuarine crustaceans and their migratory behavior, it is not known whether physiological conditions play a role in migratory activities (Creutzberg, 1975). Because M. rosenbergii can be bred and raised in laboratory facilities, it offers an opportunjty to study particular life stages and to control the environmental history of test animals. Oxygen consumption of postlarval prawns was measured at various levels of temperature and salinity in this experiment, as part of a larger study of post-larval metabolic and behavioral responses to environmental factors during the migratory phase. MATERIALS AND METHODS Post-larvae utilized in these experiments were cultured in facilities at the University of California, Davis. Culture systems were maintained at 12-14’:,,, salinity using artificial sea salts (Instant Ocean) at about 27-29°C. The young
prawns were held at these conditions until metamorphosis to the post-larval stage when individuals were randomly selected for the tests and placed in one of 12 90-liter aquaria for acclimation to experimental condiGons. All acclimation vessels contained 14’:,, salinity water at 27°C upon transfer of the post-larvae. Temperature was altered at the rate of 2°C per day and salinity by 4”,,,,per day until experimental conditions were attained. Test.conditions of 20, 27 and 34°C and 0, 7, 14, and 28”,,, salinity were selected on the basis of reports of the ranges of temperature and salinity in the animals’ natural habitat (John. 1957; Raman, 1967) and to facilitate comparisons with existing data on other life stages of the prawn (Nelson er al., 1977). Animals were held for 48 hr at the test conditions before oxygen consumption measurements were made. Forty-eight hr was considered sufficient for acclimation in light of experimental evidence on other small crustaceans (Kinne, 1964; Simmons & Knight. 1975). Post-larvae were fed thawed frozen brine shrimp adults (Artemia) daily during the acclimation process, but were not fed for 24 hr prior to oxygen consumption evaluations. The post-larvae ranged in age from 45 to lOOdays and dry weights ranged from 1.31 to 75.05 mg. Comparable wet weights are 5.20-287.94 mg. Oxygen consumption was monitored in a Gilson differential respirometer. Flasks were shaken at a rate of 84 oscillations/min. Monitoring was for two I-hr periods at constant temperature and salinity under ambient lighting between 0900 and 1700 hr. Rates of oxygen consumption reported here are the averages of the rates determined during the two monitoring periods. Since the prawns’ movements were unrestricted within the reaction flasks, the oxygen consumption values are indicative of routine metabolic rate as defined by Fry (1947). The rate of oxygen consumption (non-weight specific) is expressed as ~1 oxygen consumed per individuai per hour at STP. The relationship between oxygen consumption and body dry weight was examined for post-larvae in each treatment group (Table 1). Analysis of the data by linear regression and multiple linear regression was conducted using a 0.05 level of significance except where stated otherwise. Most of the analysis
699
0 7 14 28 0 7 14 28 0 7 I4 28
20
0.993 1.018 0.705 1.147 0.869 1.169 0.984 0.788 0.514 0.882 0.533 0.781
Slope (hl) 0.144 0.00884 0.531 -0.00602 0.506 0.140 0.300 0.574 1.130 0.539 I.114 0.753
Intercept 0.167 0.161 0.209 0.093 0.128 0.162 0.083 0.0930 0.107 0.127 0.098 0.108
SEE
0.855 0.812 0.800 0.927 0.910 0.830 0.950 0.931 0.797 0.781 0.802 0.921
R
-0.00623 0.0185 -0.295 0.147 -0.132 0.170 -0.0170 -0.212 -0.487 -0.118 - 0.468 -0.219
tb,)
____Slope 0.141 0.00660 0.530 -0.0612 0.506 0.138 0.300 0.573 1.132 0.538 1.115 0.753
intercept
0.167 0.161 0.210 0.094 0.128 0.163 0.0838 0.088 1 0.107 0.127 0.098 0.107
SEE
0.0103 0.025 1 0.487 0.298 0.317 0.211 0.0523 0.566* 0.78lt 0.165 0.762t 0.553t
R
0.6406 0.8219 0.7376 0.1458 0.5430 0.8577 0.3861 0.7453 0.6222 0.6658 0.6347 0.8605
@,I
Slope
log O2 on log wt
Juveniles
at three temperatures and four levels of
Regression of log QO, on log wt
rosrnheryii
(RI for log 01 vs log wt are significant at 0.05 level of significance. *Indicates significance at the 0.05 level and tsignificance
log QO, = log weight-specific oxygen consumption (&mg dry wt/hr), and log wt = log dry weight. All correlation coefficients at the 0.01 level for log QO, vs log wt correlation coefficients. Data on juveniles taken from Nelson et al., 1977.
14 11 15 11 13 29 16 13 16 15 16 31
N
Log 02 = log oxygen consumption (&animal/hr),
34
27
Salinity (“,,,,)
Temperature ( C)
Regression of log O2 on log wt
Post-larvae
Table 1. Regression statistics describing the relationship between rate of oxygen consumption and dry wt of post-larvae of M. salinity
Oxygen consumption of post-larval prawns utilized Statistical Programs for the Social Sciences (Nie et al., 1975). Additional tests were used to compare regressions (Smillie, 1966).
RESULTS The oxygen consumption-weight relationship for post-larvae was significantly different from that at preacclimation conditions (lp<,,, 27°C) only at 34°C in 14’?&,salinity and in fresh water (0.10 > c( 7 0.05). In both cases the rate of increase in oxygen consumption per unit increase in body weight was less than at 27°C 147&,(Table 1). The simultaneous effects of weight, temperature and salinity on oxygen consumption are described by the following equation generated by stepwise multiple linear regression in which the variables were entered in the order given in the equation: ~1 O~/animal~r
= -45274
+ 1.589W + 2.121T-
Fig. I. Oxygen consumption of post-larvae of M. rosmhergii weighing l&t5 mg at salinities of 0. 7, 14, and 28”,,,,at 27°C. Oxygen consumption values are predictions from the regression equations in Table 2.
DISCUSSION
0.102s.
where Wis dry weight (mg), Tis temperature (‘C), and S is salinity (“,,,,). The standard error of estimates made using the equation, SEE, is 18.55, the correlation coefficient, R, is 0.818, and N is 200. Oxygen consumption is not significantly affected by salinity as determined by an F-test on the regression. Oxygen consumption is related positiveiy to weight and temperature, i.e. an increase in either parameter is accompanied by an increase in oxygen consumption. When the relationship between post-larval oxygen consumption and weight, temperature and salinity was examined for each of 4 weight groups of organisms, the resulting equations revealed a significant salinity effect on oxygen consumption in animals weighing 40-49.99 mg and a greater rate of increase in oxygen consumption per unit increase in weight than experienced by animals of lower weights (Fig. 1; see also coefficients for salinity and weight, Table 2.) Regression equations were not calculated for experimental animals weighing less than t0 mg or more than $0 mg since uneven distribution of those weight classes among the experimental treatments provided a poor basis for such analysis. The equations for animals of different weight groups also suggest a temperature-weight interaction, temperature having a significantly greater effect on oxygen consumption in animals weighing 2039.99 mg than in animals weighing more or less (see coefficients for temperature (Table 2).
Eficts
of salinity on oxygen consumption
Evidence that osmotic stress can be detected as measurable differences in rate of oxygen consumption is often contradictory (Lofts, 1956; Gross, 1957; Rae, 1958; Kutty et al., 1971). In theory, energy expended in osmoregulation should be lowest at an animal’s isosmotic point (Potts, 1954; Panikkar, 1968). The isosmotic point of M. rosenbergii post-larvae is about IS?& (Sandifer et al., 1975). The data from the present study indicate no significant change in oxygen consumption with salinity, except in animals of 4049.99 mg dry wt. Variability within treatments was great, so that only subst~tiai alterations in the rate of oxygen consumption would be detected. The fact that a significant effect occurred in post-larvae at the upper end of the weight range tested suggests that prawns at that stage may undergo developmental changes causing them to respond differently to salinity. This is given further credence by the fact that juveniles averaging 110 mg dry wt (about 422 mg wet wt) show significant changes in oxygen consumption in response to salinity (Nelson er al., 1977). That the response may reflect physiological changes accompanying development is further supported by the fact that the pattern of response to salinity was the same for the larger post-larvae and the juveniles, i.e. oxygen consumption declined as salinity increased from freshwater to 28”,,,,,despite differing environmental histories. In both studies, animals were acclimated
Table 2. Multiple linear regression equations relating temperature, salinity, and weight to oxygen consumption for post-larvae of M. rosenheryii in several weight intervals Regression coefficients Weight (mg) 10-19.99 20-29.99 30-39.99 40-49.99
Temperature
Salinity
1.8993
0.0592 -0.222 0.128 - 1.201t
2.929t 3.422t 1.825*
Weight 2.9121 1.503 1.196 5.569*
Intercept
SEE
R
N
-41.707 -55.131 -64.712 - 194.734
12.325 20.172 17.204 17.808
0.683 0.691 0.798 0.771
71 38 25 20
* indicates significance at 0.05 level. i significance at 0.01 level
102
MARIAN J. STEPHENSONand ALLEN W. KNIGHT
for 48 hr to experimental conditions, but juveniles had been maintained for several months in freshwater,
larvae are unstressed salinities they would
while post-larvae had experienced a brackish water environment from hatching up to the time of acclimation for testing. Had the response to salinity been due
vironments. Young juveniles of a penaeid shrimp which migrates from a marine environment to dilute inshore waters for maturation have been reported to demonstrate a similar response (Kutty et al., 1971). In M. rosenbergii, a critical point of development seems to be reached at about 150 mg wet weight, after which a significant physiological response to salinity may influence the animals’ movements. While there is a significant increase in oxygen consumption of M. rosenbergii post-larvae with increased temperature, there is no conclusive evidence from this study that this constitutes a stressful effect. However, 34°C is near the upper lethal limit experimentally determined for juveniles (Armstrong, 1978) and the altered weight-oxygen consumption relations noted at two of the four test conditions at that temperature indicate anomalous responses at high temperature. Whether this constitutes a metabolic stress which would evoke avoidance of high temperatures by postlarval prawns can be ascertained only by behavioral studies or more detailed data on the physical parameters associated with movements of populations in the field.
to previous acclimation rather than to developmental changes, the post-larvae might have been expected to have altered oxygen consumption rates at all salinities above or below their culture conditions (12-14x,). EfSects of temperature The effects of temperature consumption are inseparable
and activity on oxygen in these data. In sub-
sequent observations of temperature effects on activity, post-larvae were sluggish and much less mobile at 20°C than at other experimental temperatures. Since post-larvae were free-swimming during these tests, any differences in activity are reflected in the variation in oxygen consumption observed between temperatures. The temperature-weight interaction detected in this study has been noted in investigations of the metabolic responses of other crustaceans (Newell, 1962; Simmons & Knight, 1975). Newell suggests starvation would affect smaller individuals more than large ones and that it is reflected in nearly temperature-independent oxygen consumption. Since post-larvae were not fed for 24 hr prior to oxygen consumption measurements, starvation could be a factor influencing sizerelated oxygen consumption in this study. There is no other evidence available to elaborate on this relationship in M. rosenbergii.
by short-term exposure to the encounter in their natural en-
Acknowledgements-This investigation was supported in part by a special appropriation to the Aquaculture Group at the University of California at Davis, from the California State Legislature, and by support from the University of California Agricultural Experiment Station.
REFERENCES Efiect of weight
Oxygen consumption in small poikilotherms generally increases with weight by a power of 0.95-1.0 of the weight of the animal and in larger organisms by a power of about 0.7 (Hemmingsen, 1960). The weightoxygen consumption relationships described by the b values for the 12 treatment groups in this study generally fit the expected pattern, the only deviants being in the freshwater and 14”/,, salinity treatments at 34°C. The oxygen consumption-weight relationship for post-larvae at 27°C 14”&, did not differ significantly from that for larvae at 28°C ll-12%” (Stephenson & Knight, 1980). Values reported for juveniles under the same experimental conditions were generally lower than those for post-larvae, as would be expected on the basis of increased size alone. Relation to natural history
Reports on the occurrence of M. rosenbergii in rivers, estuaries and backwaters of India, Pakistan, and Malaysia note salinities of 5-ZOO/, in regions where hatching and development to post-larvae take place (John, 1957; Johnson, 1967; George, 1969). Post-larvae of about 38 mm length have been observed moving upstream along the banks of streams toward the end of the dry season when evaporation, decreased freshwater outflow, and strong tidal influence increase salinity in the backwaters and estuaries (John, 1957). The data from this study suggest that young post-
ARMSTRONGD. A. (1978) Responses of Macrobrachium rosenbergii to extremes of temperature and salinity. In Studies in bioenergetics, osmoregulation, development, behavior and survival of several aquaculture organisms (Edited by Knight A. W.), pp. 18-51. Water Sci_& Eng. Paper No. 4507. Universitv of California. Davis. CREU?ZBERGF. (1975) Orientation in space: animalsinvertebrates. In Ecology: A Comprehensive, Integrated Treatise on Life in Oceans and Coastal Waters, Vol. 2, Part 2. Physiological Mechanisms (Edited by Kinne O.), pp. 555-655. Wiley, New York. FRY F. E. J. (1947) Effects of the environment on animal activity. On;. Fish. Res. Lab. 68, l-62. GEORGEM. J. (1969) Genus Macrobrachium (Bate. 18681. Prawn fisheries of’brdia. Bull. cent. mar. Fish. R& Ins;. 14, 168~216. GROSS W. J. (1957) An analysis of response to osmotic stress in selected decapod crustacea. Biol. Bull. mar. Biol. lab., Woods Hole 112, 43362. HEMMINGSEN A. M. (1960) Energy metabolism as related to body size and respiratory surfaces, and its evolution. Rep. Steno meml Hosp. 9, l-l 10.
JOHN C. M. (1957) Bionomics and life history of Macrobrachium rosenbergii (de Man). Bull. cent. res. inst. 15,
93-102. JOHNSOND. S. (1967) Some factors influencing the distribution of fresh water prawns in Malaya. ProclSymp. Crusr., Mar. Biol. Ass. India 1. 418433. KINNE 0. (1964) The effects of temperature and salinity on
marine and brackish water animals. II. Salinity and temperature salinity combinations. Oceanogr. mar. Biol. Ann. Rev. 2, 281-339. KUTTY M. N., MURUGAPOOPATHY G. & KRISHNAN T. S. (1971) Influence of salinity and temperature on the oxy-
Oxygen consumption of post-larval prawns gen consumption in young juveniles of the Indian prawn Penaeus indicus. Mar. Biol. 11, 125-131. LING S. W. & MERICANA. B. 0. (1961) Notes on the life and habits of the adults and larval stages of Macrobrachium rosenbergii (de Man). Indo-Pac. Fish. Coun. 9, 55-61. LOFTSB. (1956) The effects of salinity changes on the respiratory rate of the prawn Palaemonetes narians (Leach). J. exp. Biol. 33, 73G-736. NELSONS. G., ARMSTRONG D. A., KNIGHTA. W. & LI H. W. (1977) The effects of temperature and salinity on Macrobrachium rosenbergii (Crustacea: Palaemonidae). Comp. Biochem. Physiol. 56A, 533-537. NEWELLR. C., AHSANULLAHM. A. & PYE V. I. (1973) Aerial and aquatic respiration in the shore crab Carcinus maenas. Comb. Biochem. Physiol. 43A, 239-252.
NIE N. H.. HULL C. H.. JENKINSJ. G.. STEINGRENNER K. & BENT d. H. (1975)‘Statistical Package for rhe Social Sciences. McGraw-Hill, New York. PANIKKARN. K. (1968) Osmotic behavior of shrimps and prawns in rela&on to their biology and culture: FAO Fish. Rep. 57, 527-538.
POTS W. T. W. (1954) The energetics of osmotic regulation in brackish- and fresh-water animals. J. exp. Biol. 31, 618630. RAMANK. (1967) Observations on the fishery and biology of the giant freshwater prawn Macrobrachium rosenbergii (de Man). Proc. Symp. Crusr. Biol. Ass. India 2,649%669. RAO K. P. (1958) Oxygen consumption as a function of size and salinity in Metapenaeus monoceros FAB. from mar-
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ine and brackish water environments. J. exp. Biol. 35, 307-313. RICHARDP. (1978) Tolerance aux temperature extremes de Pnlaemon serratus (Pennant): influence de la taille et de I’acclimation. J. exp. mar. Biol. Ecol. 35, 137-146. SANDIFERP. A., HOPKINSJ. S. & SMITH T. 1. J. (1975) Observations on salinity tolerance and osmoregulation in laboratory-reared Macrobrachium rosenberyii post-larvae (Crustacea: Caridea). Aquaculmre 6, 103-l 14. SIMMONS M. A. & KNIGHTA. W. (1975) Respiratory response of Neomysis intermedia (Crustacea: Mysidacea) to changes in salinity, temperature and season. Comp. Biothem. Physiol. SOA, 181-193. SMILLIEK. W. (1966) An Introduction ro Regression and Correlation. Academic, New York. STEPHENSON M. J. & KNIGHTA. W. (1980) Growth, respiration and caloric content of larvae of the prawn Macrobrachium rosenbergii (De Man). Comp. Biochem. Physiol. 66, 385391.
ZEIN-ELDINZ. P. (1963) Effect of salinity on growth of post-larval penaeid shrimp. Biol. Bull mar. Biol. lab., Woods Hole 125, 188-196. ZEIN-ELDINZ. P. & ALDRICHD. V. (1965) Growth and survival of post-larval Penaeus azrecus under controlled conditions of temperature and salinity. Biol. Bull. mnr. Biol. lab., Woods Hole 129, 199-216. ZEIN-ELDINZ. P. & GRIFFITHG. W. (1966) The effect of temperature upon the growth of laboratory-held postlarva1 Penaeus aztecus. Biol. Bull. mar. Biol. lab.. Woods Hole 131, 186-196.
respirometer. 2. Differences in oxygen consumption among salinity treatments were not significant except in larger animals, in which oxygen consumption decreased as salinity increased. 3. Oxygen consumption increased with temperature. There was some evidence of weight dependency of the temperature response. Deviations in the weight-respiration relation at 34°C suggest high temperature is stressful. 4. These data suggest that salinity does not affect distribution of small post-larvae but may influence movements of larger animals. High temperatures may induce migrations of smaller post-larvae.
INTRODUCTION Macrobrachium rosenbergii (De Man), a giant prawn native to the Indo-Pacific region, is an active migrator between brackish and freshwater habitats. Females migrate to estuaries or brackish backwaters for the hatching of eggs; it has been demonstrated in the laboratory that brackish water is required for larval survival (Ling & Merican, 1961). Following metamorphosis, the semi-planktonic post-larvae move upstream to take up a more sedentary existence in freshwater. Changes in temperature and salinity associated with seasonal weather patterns have been suggested as stimulants for this migration (John, 1957). However, few studies have been conducted of crustacean responses to salinity and temperature during life stages associated with active migration (ZeinEtdin, 1963; Zein-Eldin & Aldrich, 1965; &in-Eldin & Griffith, 1966; Sandifer et al., 1975; Richard, 1978). While a relationship is recognized between the osmoregulatory patterns of estuarine crustaceans and their migratory behavior, it is not known whether physiological conditions play a role in migratory activities (Creutzberg, 1975). Because M. rosenbergii can be bred and raised in laboratory facilities, it offers an opportunjty to study particular life stages and to control the environmental history of test animals. Oxygen consumption of postlarval prawns was measured at various levels of temperature and salinity in this experiment, as part of a larger study of post-larval metabolic and behavioral responses to environmental factors during the migratory phase. MATERIALS AND METHODS Post-larvae utilized in these experiments were cultured in facilities at the University of California, Davis. Culture systems were maintained at 12-14’:,,, salinity using artificial sea salts (Instant Ocean) at about 27-29°C. The young
prawns were held at these conditions until metamorphosis to the post-larval stage when individuals were randomly selected for the tests and placed in one of 12 90-liter aquaria for acclimation to experimental condiGons. All acclimation vessels contained 14’:,, salinity water at 27°C upon transfer of the post-larvae. Temperature was altered at the rate of 2°C per day and salinity by 4”,,,,per day until experimental conditions were attained. Test.conditions of 20, 27 and 34°C and 0, 7, 14, and 28”,,, salinity were selected on the basis of reports of the ranges of temperature and salinity in the animals’ natural habitat (John. 1957; Raman, 1967) and to facilitate comparisons with existing data on other life stages of the prawn (Nelson er al., 1977). Animals were held for 48 hr at the test conditions before oxygen consumption measurements were made. Forty-eight hr was considered sufficient for acclimation in light of experimental evidence on other small crustaceans (Kinne, 1964; Simmons & Knight. 1975). Post-larvae were fed thawed frozen brine shrimp adults (Artemia) daily during the acclimation process, but were not fed for 24 hr prior to oxygen consumption evaluations. The post-larvae ranged in age from 45 to lOOdays and dry weights ranged from 1.31 to 75.05 mg. Comparable wet weights are 5.20-287.94 mg. Oxygen consumption was monitored in a Gilson differential respirometer. Flasks were shaken at a rate of 84 oscillations/min. Monitoring was for two I-hr periods at constant temperature and salinity under ambient lighting between 0900 and 1700 hr. Rates of oxygen consumption reported here are the averages of the rates determined during the two monitoring periods. Since the prawns’ movements were unrestricted within the reaction flasks, the oxygen consumption values are indicative of routine metabolic rate as defined by Fry (1947). The rate of oxygen consumption (non-weight specific) is expressed as ~1 oxygen consumed per individuai per hour at STP. The relationship between oxygen consumption and body dry weight was examined for post-larvae in each treatment group (Table 1). Analysis of the data by linear regression and multiple linear regression was conducted using a 0.05 level of significance except where stated otherwise. Most of the analysis
699
0 7 14 28 0 7 14 28 0 7 I4 28
20
0.993 1.018 0.705 1.147 0.869 1.169 0.984 0.788 0.514 0.882 0.533 0.781
Slope (hl) 0.144 0.00884 0.531 -0.00602 0.506 0.140 0.300 0.574 1.130 0.539 I.114 0.753
Intercept 0.167 0.161 0.209 0.093 0.128 0.162 0.083 0.0930 0.107 0.127 0.098 0.108
SEE
0.855 0.812 0.800 0.927 0.910 0.830 0.950 0.931 0.797 0.781 0.802 0.921
R
-0.00623 0.0185 -0.295 0.147 -0.132 0.170 -0.0170 -0.212 -0.487 -0.118 - 0.468 -0.219
tb,)
____Slope 0.141 0.00660 0.530 -0.0612 0.506 0.138 0.300 0.573 1.132 0.538 1.115 0.753
intercept
0.167 0.161 0.210 0.094 0.128 0.163 0.0838 0.088 1 0.107 0.127 0.098 0.107
SEE
0.0103 0.025 1 0.487 0.298 0.317 0.211 0.0523 0.566* 0.78lt 0.165 0.762t 0.553t
R
0.6406 0.8219 0.7376 0.1458 0.5430 0.8577 0.3861 0.7453 0.6222 0.6658 0.6347 0.8605
@,I
Slope
log O2 on log wt
Juveniles
at three temperatures and four levels of
Regression of log QO, on log wt
rosrnheryii
(RI for log 01 vs log wt are significant at 0.05 level of significance. *Indicates significance at the 0.05 level and tsignificance
log QO, = log weight-specific oxygen consumption (&mg dry wt/hr), and log wt = log dry weight. All correlation coefficients at the 0.01 level for log QO, vs log wt correlation coefficients. Data on juveniles taken from Nelson et al., 1977.
14 11 15 11 13 29 16 13 16 15 16 31
N
Log 02 = log oxygen consumption (&animal/hr),
34
27
Salinity (“,,,,)
Temperature ( C)
Regression of log O2 on log wt
Post-larvae
Table 1. Regression statistics describing the relationship between rate of oxygen consumption and dry wt of post-larvae of M. salinity
Oxygen consumption of post-larval prawns utilized Statistical Programs for the Social Sciences (Nie et al., 1975). Additional tests were used to compare regressions (Smillie, 1966).
RESULTS The oxygen consumption-weight relationship for post-larvae was significantly different from that at preacclimation conditions (lp<,,, 27°C) only at 34°C in 14’?&,salinity and in fresh water (0.10 > c( 7 0.05). In both cases the rate of increase in oxygen consumption per unit increase in body weight was less than at 27°C 147&,(Table 1). The simultaneous effects of weight, temperature and salinity on oxygen consumption are described by the following equation generated by stepwise multiple linear regression in which the variables were entered in the order given in the equation: ~1 O~/animal~r
= -45274
+ 1.589W + 2.121T-
Fig. I. Oxygen consumption of post-larvae of M. rosmhergii weighing l&t5 mg at salinities of 0. 7, 14, and 28”,,,,at 27°C. Oxygen consumption values are predictions from the regression equations in Table 2.
DISCUSSION
0.102s.
where Wis dry weight (mg), Tis temperature (‘C), and S is salinity (“,,,,). The standard error of estimates made using the equation, SEE, is 18.55, the correlation coefficient, R, is 0.818, and N is 200. Oxygen consumption is not significantly affected by salinity as determined by an F-test on the regression. Oxygen consumption is related positiveiy to weight and temperature, i.e. an increase in either parameter is accompanied by an increase in oxygen consumption. When the relationship between post-larval oxygen consumption and weight, temperature and salinity was examined for each of 4 weight groups of organisms, the resulting equations revealed a significant salinity effect on oxygen consumption in animals weighing 40-49.99 mg and a greater rate of increase in oxygen consumption per unit increase in weight than experienced by animals of lower weights (Fig. 1; see also coefficients for salinity and weight, Table 2.) Regression equations were not calculated for experimental animals weighing less than t0 mg or more than $0 mg since uneven distribution of those weight classes among the experimental treatments provided a poor basis for such analysis. The equations for animals of different weight groups also suggest a temperature-weight interaction, temperature having a significantly greater effect on oxygen consumption in animals weighing 2039.99 mg than in animals weighing more or less (see coefficients for temperature (Table 2).
Eficts
of salinity on oxygen consumption
Evidence that osmotic stress can be detected as measurable differences in rate of oxygen consumption is often contradictory (Lofts, 1956; Gross, 1957; Rae, 1958; Kutty et al., 1971). In theory, energy expended in osmoregulation should be lowest at an animal’s isosmotic point (Potts, 1954; Panikkar, 1968). The isosmotic point of M. rosenbergii post-larvae is about IS?& (Sandifer et al., 1975). The data from the present study indicate no significant change in oxygen consumption with salinity, except in animals of 4049.99 mg dry wt. Variability within treatments was great, so that only subst~tiai alterations in the rate of oxygen consumption would be detected. The fact that a significant effect occurred in post-larvae at the upper end of the weight range tested suggests that prawns at that stage may undergo developmental changes causing them to respond differently to salinity. This is given further credence by the fact that juveniles averaging 110 mg dry wt (about 422 mg wet wt) show significant changes in oxygen consumption in response to salinity (Nelson er al., 1977). That the response may reflect physiological changes accompanying development is further supported by the fact that the pattern of response to salinity was the same for the larger post-larvae and the juveniles, i.e. oxygen consumption declined as salinity increased from freshwater to 28”,,,,,despite differing environmental histories. In both studies, animals were acclimated
Table 2. Multiple linear regression equations relating temperature, salinity, and weight to oxygen consumption for post-larvae of M. rosenheryii in several weight intervals Regression coefficients Weight (mg) 10-19.99 20-29.99 30-39.99 40-49.99
Temperature
Salinity
1.8993
0.0592 -0.222 0.128 - 1.201t
2.929t 3.422t 1.825*
Weight 2.9121 1.503 1.196 5.569*
Intercept
SEE
R
N
-41.707 -55.131 -64.712 - 194.734
12.325 20.172 17.204 17.808
0.683 0.691 0.798 0.771
71 38 25 20
* indicates significance at 0.05 level. i significance at 0.01 level
102
MARIAN J. STEPHENSONand ALLEN W. KNIGHT
for 48 hr to experimental conditions, but juveniles had been maintained for several months in freshwater,
larvae are unstressed salinities they would
while post-larvae had experienced a brackish water environment from hatching up to the time of acclimation for testing. Had the response to salinity been due
vironments. Young juveniles of a penaeid shrimp which migrates from a marine environment to dilute inshore waters for maturation have been reported to demonstrate a similar response (Kutty et al., 1971). In M. rosenbergii, a critical point of development seems to be reached at about 150 mg wet weight, after which a significant physiological response to salinity may influence the animals’ movements. While there is a significant increase in oxygen consumption of M. rosenbergii post-larvae with increased temperature, there is no conclusive evidence from this study that this constitutes a stressful effect. However, 34°C is near the upper lethal limit experimentally determined for juveniles (Armstrong, 1978) and the altered weight-oxygen consumption relations noted at two of the four test conditions at that temperature indicate anomalous responses at high temperature. Whether this constitutes a metabolic stress which would evoke avoidance of high temperatures by postlarval prawns can be ascertained only by behavioral studies or more detailed data on the physical parameters associated with movements of populations in the field.
to previous acclimation rather than to developmental changes, the post-larvae might have been expected to have altered oxygen consumption rates at all salinities above or below their culture conditions (12-14x,). EfSects of temperature The effects of temperature consumption are inseparable
and activity on oxygen in these data. In sub-
sequent observations of temperature effects on activity, post-larvae were sluggish and much less mobile at 20°C than at other experimental temperatures. Since post-larvae were free-swimming during these tests, any differences in activity are reflected in the variation in oxygen consumption observed between temperatures. The temperature-weight interaction detected in this study has been noted in investigations of the metabolic responses of other crustaceans (Newell, 1962; Simmons & Knight, 1975). Newell suggests starvation would affect smaller individuals more than large ones and that it is reflected in nearly temperature-independent oxygen consumption. Since post-larvae were not fed for 24 hr prior to oxygen consumption measurements, starvation could be a factor influencing sizerelated oxygen consumption in this study. There is no other evidence available to elaborate on this relationship in M. rosenbergii.
by short-term exposure to the encounter in their natural en-
Acknowledgements-This investigation was supported in part by a special appropriation to the Aquaculture Group at the University of California at Davis, from the California State Legislature, and by support from the University of California Agricultural Experiment Station.
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