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Influence of ambient salinity on plasma Ca2+ and Mg2+ levels in juvenile Mugil cephalus L
Crimp. Biochem. Phwiol. Printed in Great Bhtain
Vol. %A, No. 2, pp. 335-338,
1983
0300-9629/83 $3.00 + 0.00 si”, ,.l 1983 Pergamon Press Ltd
INFLUENCE OF AMBIENT SALINITY ON PLASMA Ca*+ AND Mg”+ LEVELS IN JUVENILE MUGIL CEPHALUS L. FRANK G. NORDLIEand JOAN WHITTIER Department of Zoology, University of Florida, Gainesville, FL 32611, U.S.A. Telephone: 904-392-l 107 (Received 25 January 1983)
Abstract-l. Plasma Ca*+ and Mg?+ concentrations showed no statistically significant differences among juvenile Mugil cephalus acclimated to a series of ambient salinities ranging from fresh water to full sea water. 2. The overall mean concentration of plasma Ca*+ was found to be 2.55 + 0.68 mM/l and of Mg*+, 1.89 & 0.67 mM/l. 3. These values were found to be near the median values among other euryhaline teleosts, but near the lower end of the range of values for plasma Ca*+ and Mg’+ among stenohahne teleosts, suggesting a narrower range of plasma concentrations of these cations among euryhatine species than among stenohahne forms.
INTRODUCTION Calcium (Caz*) and magnesium (MS*+) are the two most abundant cations in sea water. Their concentrations vary somewhat among waters, with mean values of 9.98 mM/l (Ca*+) and 52.30 mM/l (Mg*+) in sea water with a Cl- concentration of 535.30mM/l (Nicol, 1960). The order of abundance is reversed in typical fresh waters with calcium being the more abundant of the two cations, and also with concentrations of both much reduced from their levels in sea water (Wetzel, 1975). Calcium is the most abundant cation in the vertebrate body (Dacke, I979), much of it being present in bone, while there is no such large compartment of Mg*+ present. However, neither of these cations is very abundant in vertebrate plasma, and in particular that of teleost fishes. Interest in the regulation of plasma levels of these two cations among lower vertebrates was stimulated by the obvious disparity between ambient environmental levels of the ions and those found in the plasma and their demonstrated precise regulation in the higher vertebrates, mammals in particular. It appeared from a casual perusal of existing information on plasma Ca’+ concentrations of the fish-like vertebrates that there was appreciable variation in the level at which this ion was regulated among various species within a group (e.g. the teleostei), as well as among the various groups of fish-like vertebrates (reviews by Holmes and Donaldson, 1969; Natochin and Lavrova, 1974; Dacke, 1979). While much of the demonstrated variation was among species, there could also be significant variations within species, as Lutz (I 972) stated that there was no tight regulation of’ Ca” in the teleost fishes. However, he also stated that Mg2” was the most tightly regulated divalent cation in plasma of this group of vertebrates. The question of how tightly either of these ions is regulated takes on an additional complexity when asked of euryhaline forms living in or acclimated to a wide range of ambient salinities.
The work to be presented in this paper evaluated the regulation of plasma Ca’+ and Mg’+ concentrations over the range of ambient salinities from fresh water to full sea water in the euryhaline teleost, Mugil cephalus L. The analyses were carried out utilizing juvenile individuals collected during a single season of the year (summer), to minimize possible influences of size as demonstrated by Houston (I 969) in steelhead trout and seasonal variations in levels of regulation of either of these cations as demonstrated by Woodhead (1968) in sexually mature Arctic cod and by Khawaja and Jafri (1970) in juvenile Cirrhina mriguiu.
MATERIAIS AND
METHODS
The experimental fish (juvenile Mugil cephalus-mean length 10.5 cm, range 7.5-23.7 cm) were obtained by use of a cast net from waters of the Matanzas Inlet near Marineland, St. Johns Co., Florida, during summer months. Fish were transported to the laboratory in Gainesville, Florida, where groups of individuals were placed into each of the acclimation salinities of 100X. 50”/: and 250,: sea water and fresh water. The sea water”diluGons were produced by adding appropriate quantities of deionized water to filtered Atlantic ocean water (Ca*+ = 9.61 + 0.49 mM/l and Mg2+ = 54.36 + 4.42 mM/l) obtained from Marineland of Florida. Fresh water was dechlorinated tap water (Ca 2+ = 0.75 & 0.12 mM/ and Mg*+ of 0.69 i 0.13 mM/l). Experimental fish groups were acclimated in aerated tanks for a period of 2 weeks at a temperature of 20 rt 1°C and a 1ight:dark cycle of 12 hr: 12 hr prior to blood sampling. The fish were treated with tetracycline to reduce the incidence of infections, and they were fed a diet of Tetramin@ during the a~Iimation period. Btood was collected from the caudal artery as described by Nordlie and Leffler (1975). Following centrifugation, the plasma from a single individual or a pooled sample from two or more individuals (determined by quantity of plasma available) was appropriately diluted. Analyses were run on a Varian atomic absorption spectrophotometer using a nitrous oxide/acetylene flame. Samples and standards were prepared in a diluent containing 2 g/l KCI and 10 g/l NaCI.
335
336
FKANK G. NORDLK and
JOAN WHITTIER
plasma levels of these cations over a range of salinities, the regulatory mechanisms in this species appear to be quite good. It is difficult to make rigorous comparisons between data obtained in the present study and those from many other previous studies because the enRESULTS vironmental conditions under which the organisms Piasma Ca’+ and Mg’+ concentrations (means, were maintained or from which they were taken were along with SD and N) for each of the acclimation rarely fully elaborated. Keeping in mind possible groups are found in Table 1. Plasma Ca2+ values limitations of such comparisons because of possible ranged from a low of 2.39 + 0.88 mM/l in individuals differences in environmental temperature, age and/or acclimated to the lOOo/,seawater medium to a high size of individuals, season of the year, etc., available of 2.85 f 0.55 mM/l in fish from the 25% seawater data on the levels of plasma Ca’+ and Mg” among bath. However, there were no statistically significant teieost fishes were compared. Holmes and Donaldson differences in plasma Ca*+ concentrations among the (1969) reviewed much of the existing information on four acclimation groups. euryhaline forms for which there were data on indiThe range in plasma Mg2+ concentrations over this viduals taken from fresh water as well as from salt ambient salinity series was slightly greater, ranging water. Utilizing the data present in that review along from a low of 1.39 + 0.023 mM/l in fresh waterwith values for Fun~~i~,~ ~~et~r(~~litus from Pickford et acclimated fish to a high of 2.13 j: 0.95 mM/I in fish al. (1969) allows for several conclusions and/or comacclimated to 257; sea water. Again, however, there parisons to be made. The ranges of plasma Cal+ were no statistically significant differences among concentrations from individuals of euryhaline teleosts mean Mg2+ concentrations of any of the acclimation acclimated to or living in fresh water ranged from groups. Because of the lack of significant differences I .03 mM/l in Oncorhynchus k~tu (Lysaya, 1951) to it was considered legitimate to calculate a mean 3.45mM/l in Salon s&r (Parry. 1961). For Ca” combining Ca2+ values over all salinities and simi- concentrations from individuals in sea water, the larly a mean combining Mg’+ values over all salinirange extended from 1.O m M: 1 in ~~~~~~r~.~~~i?~.s ties, for the purpose of making general comparisons ~~c~ff~~~~c~u (Urist and Van de Putte, 196’7) to with data from other studies. The composite means 3.43 mM/I in Sulmo sahr (Parry, 1961). The median obtained in these calculations were 2.55 + 0.68 mM/l values were 2.29 mM/l (N = 14) for individuals taken for Ca2+ and 1.89 + 0.67 mM/l for Mg’+. from fresh water and 2.30 mM/I (N = 12) for individuals taken from sea water. For Mg”’ the range of values in freshwater individuals extended from DlSCIJSSiON AND CONCLUSiONS 0.18 mM/l in O~~~I~~~~~~~Z~.S nerku (Idler and Tsuyuki, Plasma Ca’-+ and Mg’+ concentrations in juvenile 1958) to 3.04 mM/l in Anguik wzguilkr (Chan et ((I., mullet acclimated to ambient salinities of lOO%, 50% 1967) and for those acclimated to or living in sea and 25% sea water and fresh water at an environwater the range was from 0.9 mM/l in Oncorl~ynchus mental temperature of 20 k 1°C and a 12 hr: 12 hr tshawytscha (Urist and Van de Putte, 1967) to 1ight:dark cycle were found to show no significant 4.18mM/l in Anguiliu anguillu (Chan rt ul.. 1967). differences among mean concentrations of either of The values for plasma Cal’ and Mg” for juvenile the ions. However, there appeared to be more vari~~~~/ ~e~~u~~s acclimated to fresh and to sea water ation among groups in Mg’+ levels than in those of fall near the middle of these distributions for euCal+. It appears that while there is some variation in ryhaline forms. There would appear to be little difference in the ranges of plasma levels of Ca? ’ and of Mg’+ in euryhaline teleosts taken from fresh water Table 1. Plasma Cal+ and Mg’+ concentrations (mM/l) as as contrasted with the respective levels in individuals functions of a series of ambient salinities in juvenile ~~~~~~ taken from marine habitats. This conclusion would cepfirrlus be consistent with the lack of significant differences in either plasma Ca” or Mg’+ levels between Concentrations in plasma Cal’ Mg’+ freshwater- and seawater-acclimated juvenile Mugit Ambient salinity -__-_ ._~_ cephalus. However, if one compares values for Fresh water R 2.52 1.39 freshwater- versus saltwater-acclimated individuals 0.023 SD 0.16 on a species by species basis (from the data cited in N* 13116) g (lb) the Holmes and Donaldson review, 1969, and from ZSs/;, seawater ‘i?; 2.58 1.66 Pickford et ul., 1969) nine of twelve cases for Ca” 0.67 SD 0.30 and three of five for Mg2+ showed increased plasma N* lO(42) 13 (42) levels of the ions in individuals taken from sea water 50% seawater R 2.13 2.85 over those taken from fresh water (though statistical OS5 0.95 SD significance was not determined). In the notable N* 23 (37) 19 (37) exceptions to the trend of slight increases in plasma 2.39 1.95 100%seawater x levels of these ions at higher ambient salinities, it is SD 0.88 0.39 possible that the elevated plasma Ca” and Mg”’ N* 34 (SO) 33 (50) levels in individuals from fresh water were associated with seasonal activity in such species as Oncorhynchus *Numbers outside parentheses are numbers of pooled samtshaw_~~tscha (from work of Urist and Van de Putte, ples analyzed, numbers in parentheses are numbers of fish from which samples were taken. 1967). However, it remains to be demonstrated Statistical comparisons were carried out using the Student NewmanKeuls procedure for comparisons among means (Sokal and Rohlf, 1969). Significance was accepted at the 0.05 level.
Plasma Ca’+ and M$’ whether or not sexually mature individuals of such anadromous species do show significant seasonal variations in plasma levels of CaZt and/or Mg2+. Plasma Ca2+ and Mg2+ values for Mugil eephalus were also compared with those of a series of stenohaline marine teleost species. The ranges of values for such species were found to be greater than they were for euryhaline forms, with values for plasma Ca’+ ranging from a low of 1.75 mM/l in Crenilubrus tunica (Natochin and Lavrova, 1974) to a high of X.5mM/I in ~p~teroide~~ ~zacaiafz~s(Smith. 1929). For Mg’+ the values range from a low of O.SmM/l in Lophius americanus (Forster and Berglund, 1956) to a high of 9.7 mM/l in ~~~~~a~~~.~ (Edwards and Condorelli. 1928). The values for both plasma Ca’+ and Mg2+ as evidenced from the composite means of 2.55 + 0.8 mM/I (Ca2’) and 1.89 i: 0.7 mM/l (Mg’+), obtained in the present study for ~~~i~ cephalus, are near the lower ends of the ranges for both of these ions among stenohahne teleosts, though as was previously shown, quite in fine with those of other euryhaline forms. There are other plasma Ca2+ values available for Mugil cephaius from the work of Peterson and Shehadeh (1971) who reported concentrations of 3.52 mM/l from large adult males and 3.12 mM/I From large adult females. These values are higher than those obtained for juvenile mullet in the present study. Unfortunately, Peterson and Shehadeh did not provide information on environmental conditions under which their fish had been maintained, and thus any basis for the difference in plasma Ca*+ between adult and juvenile mullet can only be speculative. One might suspect a possible size relationship here in the regulation of plasma Ca?+. However, that demonstrated by Houston (1959) for plasma Ca2-+ in steelhead trout was in the other direction with the plasma level being reduced with an increase in size of individuals. Also, Nordlie t7t al. (I982) demonstrated that IVU$ cephulus, upon reaching a size of 5.5 cm, had reached a more or less stabIe plasma osmotic concentration (for a given set of environmental conditions). It would seem more likely that a cation such as Cal+ might be varying seasonally with reproductive condition. but within such limits that these variations might be hidden in experimental errors of determining plasma osmotic concentrations. Data for the related species, Mu& auratus, taken from the Black Sea, were given by Natochin and Lavrova (1974). Plasma Ca” was found to be 5.35 f 0.85 mM/l and Mg’+ 6.75 f 0.35 mM/l in this form, both of which values exceed by more than twice the plasma concentrations of Ca” + and Mg’+ respectively, obtained for juvenile Mugil cephalus in the present work. There is no obvious explanation for such differences between mullets. Again, it is regrettable that details of the environmental conditions from which individuals of M. auratus were taken and reproductive state of these individuals were not presented. In general it appears that euryhaline teleosts show less variation among species in levels at which plasma Ca2+ and Mg” are regulated compared with stenohaline teleost species, and the ranges of both of these cations in euryhaline forms are in the lower portions of the ranges of plasma concentrations of both ions among stenohaline forms. There are several possible
levels in Mugil cephulus
337
bases for the extent of variation noted in CaZ+ and Mg’+ concentrations among various species. Environmental conditions were rarely controlled or even noted for most of the species sampled. Certain environmental variations might produce rather significant variations in plasma cation levels. Sizes of individuals sampled might also introduce biases into the data. Also, it is quite possible that some of the higher values noted for both Ca” and Mg2+ were associated with seasonal reproductive activity. It is also possible that the accuracy of techniques vary and that some of the values, especially from older work, may be less reliable than those obtained using the best instrumentation now available. Future work involving more rigorously defined environmental conditions and technical refinements should include a reconsideration of some of the species previously studied. A~,knou,led~emPnts-The authors extend their appreciation to Dr W. E. S. Carr of the Whitney Marine Laboratory who helped with the coiiecting of juvenile mullet and MS Grace Russell who typed the manuscript. REFERENCES Chan D. K. 0.. Chester-Jones f., Henderson E. W. and Rankin J. C. (1967) Studies on the experimental alteration of water and electrolyte composition of the eel (An@& ~inguillo L.). .I. Endocr. 37, 297.-317. Dacke C. G. (I 979) Calcium Regulation in Sub-Mammalian Vertebrates. Academic Press, London. Edwards J. G. and Condorelli L. (1928) Electrolytes in blood and urine of fish. Am. f. Physiol. 86, 383-398. Forster R. P. and Berglund F. (1956) Osmotic diuresis and its effect on total electrolyte distribution in plasma and urine of the aglomerular teIeost, Lopkiux umericanus. J. gen. Ph_wiol. 39, 349-359. Holmes W. N. and Donaldson E. M. (1969) The body and the distribution of electrolytes. In Fish Physiology. Vol. I (Edited by Hoar W. S. and Randall D. J.), pp. l-79. Academic Press, London. Houston A. H. (1959) Osmoregulatory adaptation of stee head trout Salmo gairdneri (Richardson) to sea water. &n. J. Zool. 37, 729-748. Idler D. R. and Tsuyuki H. (1958) Biochemical studies on sockeye salmon during spawning migration--I. Physical measurements, plasma cholesterol. and electrolyte levels. Curl J. Biochem. Pk_vsiof. 36, 783~-791. Khawaja D. K. and Jafri A. K. (1970) Seasonal cycle of calcium and phosphorus in juveniles of the common carp, Cirrkina mri.gaia. Co~piu 1970, 190- 192. Lutz P. L. (l972) Body ~ompartnlentalization and ion distribution in the teleost Perca ,jfwiati/i.~. Camp. Biockem. Physiol. 41A, I81 -193. Lysaya N. M. (1951) Changes in the blood composition of salmon during the spawning migration. IX. /jkhookean. naurhn.-issied. Inst. Rj%. Kkoz. Okeanogr. 35, 47-60. (Quoted by Holmes and Donaldson. 1969). Natochin Y. V. and Lavrova E. A. (1974) The influence of water salinity and stage in life history on ion concentration of fish blood serum. J. Fish Biol. 6, 545555.5. Nicol J. A. C. (1960) Tke Biology of Marine Animuls. Interscience Publishing. New York. Nordlie F. G. and LefBer C. W. (1975) Ionic regulation and the energetics of osmoregulation in MugiL cepkalus Lin. Camp. Biockem. Pkysiol. 51 A, 125 I3 1. Nordlie F. G., Szehstowski W. A. and Nordlie W. C. (1982) Ontogenesis of osmotic regulation in the striped mullet, Mugil cepkalus L. J. Fish Biol. 20, 79-86. Parry G. (1961) Osmotic and ionic changes in blood and muscle of migrating salmonids. .I. esp. &of. 38, 41 i-427.
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FRANK G. NORDLIE and JOAN WHITTIER
Peterson G. L. and Shehadeh Z. H. (197 1) Changes in blood components of the mullet, Mugil cephalus L., following treatment with salmon gonadotropin and methyl testosterone. Comp. Biochem. Physiol. 38B, 451-457. Pickford G. E., Grant F. B. and Umminger B. L. (1969) Studies on the blood serum of the euryhaline cyprinodont fish, Fundulus heteroclitus adapted to fresh or to salt water. Trans. Corm. Acad. Arts Sri. 43, 25-70. Smith H. W. (1929) The composition of the body fluids of the goose fish (Lophius piscatorius). J. biol. Chem. 82, 71-75.
Sokal R. R. and Rohlf F. J. (1969) Biometry. W. H. Freeman, San Francisco. Uris1 M. R. and Van de Putte K. A. (1967) Comparative biochemistry of the blood of fishes. In Sharks, Skates and Rays (Edited by Gilbert P. W., Mathewson R. F. and Rail D. P.). Johns Hopkins Press, Baltimore. Wetzel R. G. (1975) Limnology. W. B. Saunders, Philadelphia. Woodhead P. M. J. (1968) Seasonal changes in the calcium content of the blood of arctic cod. J. mar. biol. Ass. U.K. 48, 81-91.
Vol. %A, No. 2, pp. 335-338,
1983
0300-9629/83 $3.00 + 0.00 si”, ,.l 1983 Pergamon Press Ltd
INFLUENCE OF AMBIENT SALINITY ON PLASMA Ca*+ AND Mg”+ LEVELS IN JUVENILE MUGIL CEPHALUS L. FRANK G. NORDLIEand JOAN WHITTIER Department of Zoology, University of Florida, Gainesville, FL 32611, U.S.A. Telephone: 904-392-l 107 (Received 25 January 1983)
Abstract-l. Plasma Ca*+ and Mg?+ concentrations showed no statistically significant differences among juvenile Mugil cephalus acclimated to a series of ambient salinities ranging from fresh water to full sea water. 2. The overall mean concentration of plasma Ca*+ was found to be 2.55 + 0.68 mM/l and of Mg*+, 1.89 & 0.67 mM/l. 3. These values were found to be near the median values among other euryhaline teleosts, but near the lower end of the range of values for plasma Ca*+ and Mg’+ among stenohahne teleosts, suggesting a narrower range of plasma concentrations of these cations among euryhatine species than among stenohahne forms.
INTRODUCTION Calcium (Caz*) and magnesium (MS*+) are the two most abundant cations in sea water. Their concentrations vary somewhat among waters, with mean values of 9.98 mM/l (Ca*+) and 52.30 mM/l (Mg*+) in sea water with a Cl- concentration of 535.30mM/l (Nicol, 1960). The order of abundance is reversed in typical fresh waters with calcium being the more abundant of the two cations, and also with concentrations of both much reduced from their levels in sea water (Wetzel, 1975). Calcium is the most abundant cation in the vertebrate body (Dacke, I979), much of it being present in bone, while there is no such large compartment of Mg*+ present. However, neither of these cations is very abundant in vertebrate plasma, and in particular that of teleost fishes. Interest in the regulation of plasma levels of these two cations among lower vertebrates was stimulated by the obvious disparity between ambient environmental levels of the ions and those found in the plasma and their demonstrated precise regulation in the higher vertebrates, mammals in particular. It appeared from a casual perusal of existing information on plasma Ca’+ concentrations of the fish-like vertebrates that there was appreciable variation in the level at which this ion was regulated among various species within a group (e.g. the teleostei), as well as among the various groups of fish-like vertebrates (reviews by Holmes and Donaldson, 1969; Natochin and Lavrova, 1974; Dacke, 1979). While much of the demonstrated variation was among species, there could also be significant variations within species, as Lutz (I 972) stated that there was no tight regulation of’ Ca” in the teleost fishes. However, he also stated that Mg2” was the most tightly regulated divalent cation in plasma of this group of vertebrates. The question of how tightly either of these ions is regulated takes on an additional complexity when asked of euryhaline forms living in or acclimated to a wide range of ambient salinities.
The work to be presented in this paper evaluated the regulation of plasma Ca’+ and Mg’+ concentrations over the range of ambient salinities from fresh water to full sea water in the euryhaline teleost, Mugil cephalus L. The analyses were carried out utilizing juvenile individuals collected during a single season of the year (summer), to minimize possible influences of size as demonstrated by Houston (I 969) in steelhead trout and seasonal variations in levels of regulation of either of these cations as demonstrated by Woodhead (1968) in sexually mature Arctic cod and by Khawaja and Jafri (1970) in juvenile Cirrhina mriguiu.
MATERIAIS AND
METHODS
The experimental fish (juvenile Mugil cephalus-mean length 10.5 cm, range 7.5-23.7 cm) were obtained by use of a cast net from waters of the Matanzas Inlet near Marineland, St. Johns Co., Florida, during summer months. Fish were transported to the laboratory in Gainesville, Florida, where groups of individuals were placed into each of the acclimation salinities of 100X. 50”/: and 250,: sea water and fresh water. The sea water”diluGons were produced by adding appropriate quantities of deionized water to filtered Atlantic ocean water (Ca*+ = 9.61 + 0.49 mM/l and Mg2+ = 54.36 + 4.42 mM/l) obtained from Marineland of Florida. Fresh water was dechlorinated tap water (Ca 2+ = 0.75 & 0.12 mM/ and Mg*+ of 0.69 i 0.13 mM/l). Experimental fish groups were acclimated in aerated tanks for a period of 2 weeks at a temperature of 20 rt 1°C and a 1ight:dark cycle of 12 hr: 12 hr prior to blood sampling. The fish were treated with tetracycline to reduce the incidence of infections, and they were fed a diet of Tetramin@ during the a~Iimation period. Btood was collected from the caudal artery as described by Nordlie and Leffler (1975). Following centrifugation, the plasma from a single individual or a pooled sample from two or more individuals (determined by quantity of plasma available) was appropriately diluted. Analyses were run on a Varian atomic absorption spectrophotometer using a nitrous oxide/acetylene flame. Samples and standards were prepared in a diluent containing 2 g/l KCI and 10 g/l NaCI.
335
336
FKANK G. NORDLK and
JOAN WHITTIER
plasma levels of these cations over a range of salinities, the regulatory mechanisms in this species appear to be quite good. It is difficult to make rigorous comparisons between data obtained in the present study and those from many other previous studies because the enRESULTS vironmental conditions under which the organisms Piasma Ca’+ and Mg’+ concentrations (means, were maintained or from which they were taken were along with SD and N) for each of the acclimation rarely fully elaborated. Keeping in mind possible groups are found in Table 1. Plasma Ca2+ values limitations of such comparisons because of possible ranged from a low of 2.39 + 0.88 mM/l in individuals differences in environmental temperature, age and/or acclimated to the lOOo/,seawater medium to a high size of individuals, season of the year, etc., available of 2.85 f 0.55 mM/l in fish from the 25% seawater data on the levels of plasma Ca’+ and Mg” among bath. However, there were no statistically significant teieost fishes were compared. Holmes and Donaldson differences in plasma Ca*+ concentrations among the (1969) reviewed much of the existing information on four acclimation groups. euryhaline forms for which there were data on indiThe range in plasma Mg2+ concentrations over this viduals taken from fresh water as well as from salt ambient salinity series was slightly greater, ranging water. Utilizing the data present in that review along from a low of 1.39 + 0.023 mM/l in fresh waterwith values for Fun~~i~,~ ~~et~r(~~litus from Pickford et acclimated fish to a high of 2.13 j: 0.95 mM/I in fish al. (1969) allows for several conclusions and/or comacclimated to 257; sea water. Again, however, there parisons to be made. The ranges of plasma Cal+ were no statistically significant differences among concentrations from individuals of euryhaline teleosts mean Mg2+ concentrations of any of the acclimation acclimated to or living in fresh water ranged from groups. Because of the lack of significant differences I .03 mM/l in Oncorhynchus k~tu (Lysaya, 1951) to it was considered legitimate to calculate a mean 3.45mM/l in Salon s&r (Parry. 1961). For Ca” combining Ca2+ values over all salinities and simi- concentrations from individuals in sea water, the larly a mean combining Mg’+ values over all salinirange extended from 1.O m M: 1 in ~~~~~~r~.~~~i?~.s ties, for the purpose of making general comparisons ~~c~ff~~~~c~u (Urist and Van de Putte, 196’7) to with data from other studies. The composite means 3.43 mM/I in Sulmo sahr (Parry, 1961). The median obtained in these calculations were 2.55 + 0.68 mM/l values were 2.29 mM/l (N = 14) for individuals taken for Ca2+ and 1.89 + 0.67 mM/l for Mg’+. from fresh water and 2.30 mM/I (N = 12) for individuals taken from sea water. For Mg”’ the range of values in freshwater individuals extended from DlSCIJSSiON AND CONCLUSiONS 0.18 mM/l in O~~~I~~~~~~~Z~.S nerku (Idler and Tsuyuki, Plasma Ca’-+ and Mg’+ concentrations in juvenile 1958) to 3.04 mM/l in Anguik wzguilkr (Chan et ((I., mullet acclimated to ambient salinities of lOO%, 50% 1967) and for those acclimated to or living in sea and 25% sea water and fresh water at an environwater the range was from 0.9 mM/l in Oncorl~ynchus mental temperature of 20 k 1°C and a 12 hr: 12 hr tshawytscha (Urist and Van de Putte, 1967) to 1ight:dark cycle were found to show no significant 4.18mM/l in Anguiliu anguillu (Chan rt ul.. 1967). differences among mean concentrations of either of The values for plasma Cal’ and Mg” for juvenile the ions. However, there appeared to be more vari~~~~/ ~e~~u~~s acclimated to fresh and to sea water ation among groups in Mg’+ levels than in those of fall near the middle of these distributions for euCal+. It appears that while there is some variation in ryhaline forms. There would appear to be little difference in the ranges of plasma levels of Ca? ’ and of Mg’+ in euryhaline teleosts taken from fresh water Table 1. Plasma Cal+ and Mg’+ concentrations (mM/l) as as contrasted with the respective levels in individuals functions of a series of ambient salinities in juvenile ~~~~~~ taken from marine habitats. This conclusion would cepfirrlus be consistent with the lack of significant differences in either plasma Ca” or Mg’+ levels between Concentrations in plasma Cal’ Mg’+ freshwater- and seawater-acclimated juvenile Mugit Ambient salinity -__-_ ._~_ cephalus. However, if one compares values for Fresh water R 2.52 1.39 freshwater- versus saltwater-acclimated individuals 0.023 SD 0.16 on a species by species basis (from the data cited in N* 13116) g (lb) the Holmes and Donaldson review, 1969, and from ZSs/;, seawater ‘i?; 2.58 1.66 Pickford et ul., 1969) nine of twelve cases for Ca” 0.67 SD 0.30 and three of five for Mg2+ showed increased plasma N* lO(42) 13 (42) levels of the ions in individuals taken from sea water 50% seawater R 2.13 2.85 over those taken from fresh water (though statistical OS5 0.95 SD significance was not determined). In the notable N* 23 (37) 19 (37) exceptions to the trend of slight increases in plasma 2.39 1.95 100%seawater x levels of these ions at higher ambient salinities, it is SD 0.88 0.39 possible that the elevated plasma Ca” and Mg”’ N* 34 (SO) 33 (50) levels in individuals from fresh water were associated with seasonal activity in such species as Oncorhynchus *Numbers outside parentheses are numbers of pooled samtshaw_~~tscha (from work of Urist and Van de Putte, ples analyzed, numbers in parentheses are numbers of fish from which samples were taken. 1967). However, it remains to be demonstrated Statistical comparisons were carried out using the Student NewmanKeuls procedure for comparisons among means (Sokal and Rohlf, 1969). Significance was accepted at the 0.05 level.
Plasma Ca’+ and M$’ whether or not sexually mature individuals of such anadromous species do show significant seasonal variations in plasma levels of CaZt and/or Mg2+. Plasma Ca2+ and Mg2+ values for Mugil eephalus were also compared with those of a series of stenohaline marine teleost species. The ranges of values for such species were found to be greater than they were for euryhaline forms, with values for plasma Ca’+ ranging from a low of 1.75 mM/l in Crenilubrus tunica (Natochin and Lavrova, 1974) to a high of X.5mM/I in ~p~teroide~~ ~zacaiafz~s(Smith. 1929). For Mg’+ the values range from a low of O.SmM/l in Lophius americanus (Forster and Berglund, 1956) to a high of 9.7 mM/l in ~~~~~a~~~.~ (Edwards and Condorelli. 1928). The values for both plasma Ca’+ and Mg2+ as evidenced from the composite means of 2.55 + 0.8 mM/I (Ca2’) and 1.89 i: 0.7 mM/l (Mg’+), obtained in the present study for ~~~i~ cephalus, are near the lower ends of the ranges for both of these ions among stenohahne teleosts, though as was previously shown, quite in fine with those of other euryhaline forms. There are other plasma Ca2+ values available for Mugil cephaius from the work of Peterson and Shehadeh (1971) who reported concentrations of 3.52 mM/l from large adult males and 3.12 mM/I From large adult females. These values are higher than those obtained for juvenile mullet in the present study. Unfortunately, Peterson and Shehadeh did not provide information on environmental conditions under which their fish had been maintained, and thus any basis for the difference in plasma Ca*+ between adult and juvenile mullet can only be speculative. One might suspect a possible size relationship here in the regulation of plasma Ca?+. However, that demonstrated by Houston (1959) for plasma Ca2-+ in steelhead trout was in the other direction with the plasma level being reduced with an increase in size of individuals. Also, Nordlie t7t al. (I982) demonstrated that IVU$ cephulus, upon reaching a size of 5.5 cm, had reached a more or less stabIe plasma osmotic concentration (for a given set of environmental conditions). It would seem more likely that a cation such as Cal+ might be varying seasonally with reproductive condition. but within such limits that these variations might be hidden in experimental errors of determining plasma osmotic concentrations. Data for the related species, Mu& auratus, taken from the Black Sea, were given by Natochin and Lavrova (1974). Plasma Ca” was found to be 5.35 f 0.85 mM/l and Mg’+ 6.75 f 0.35 mM/l in this form, both of which values exceed by more than twice the plasma concentrations of Ca” + and Mg’+ respectively, obtained for juvenile Mugil cephalus in the present work. There is no obvious explanation for such differences between mullets. Again, it is regrettable that details of the environmental conditions from which individuals of M. auratus were taken and reproductive state of these individuals were not presented. In general it appears that euryhaline teleosts show less variation among species in levels at which plasma Ca2+ and Mg” are regulated compared with stenohaline teleost species, and the ranges of both of these cations in euryhaline forms are in the lower portions of the ranges of plasma concentrations of both ions among stenohaline forms. There are several possible
levels in Mugil cephulus
337
bases for the extent of variation noted in CaZ+ and Mg’+ concentrations among various species. Environmental conditions were rarely controlled or even noted for most of the species sampled. Certain environmental variations might produce rather significant variations in plasma cation levels. Sizes of individuals sampled might also introduce biases into the data. Also, it is quite possible that some of the higher values noted for both Ca” and Mg2+ were associated with seasonal reproductive activity. It is also possible that the accuracy of techniques vary and that some of the values, especially from older work, may be less reliable than those obtained using the best instrumentation now available. Future work involving more rigorously defined environmental conditions and technical refinements should include a reconsideration of some of the species previously studied. A~,knou,led~emPnts-The authors extend their appreciation to Dr W. E. S. Carr of the Whitney Marine Laboratory who helped with the coiiecting of juvenile mullet and MS Grace Russell who typed the manuscript. REFERENCES Chan D. K. 0.. Chester-Jones f., Henderson E. W. and Rankin J. C. (1967) Studies on the experimental alteration of water and electrolyte composition of the eel (An@& ~inguillo L.). .I. Endocr. 37, 297.-317. Dacke C. G. (I 979) Calcium Regulation in Sub-Mammalian Vertebrates. Academic Press, London. Edwards J. G. and Condorelli L. (1928) Electrolytes in blood and urine of fish. Am. f. Physiol. 86, 383-398. Forster R. P. and Berglund F. (1956) Osmotic diuresis and its effect on total electrolyte distribution in plasma and urine of the aglomerular teIeost, Lopkiux umericanus. J. gen. Ph_wiol. 39, 349-359. Holmes W. N. and Donaldson E. M. (1969) The body and the distribution of electrolytes. In Fish Physiology. Vol. I (Edited by Hoar W. S. and Randall D. J.), pp. l-79. Academic Press, London. Houston A. H. (1959) Osmoregulatory adaptation of stee head trout Salmo gairdneri (Richardson) to sea water. &n. J. Zool. 37, 729-748. Idler D. R. and Tsuyuki H. (1958) Biochemical studies on sockeye salmon during spawning migration--I. Physical measurements, plasma cholesterol. and electrolyte levels. Curl J. Biochem. Pk_vsiof. 36, 783~-791. Khawaja D. K. and Jafri A. K. (1970) Seasonal cycle of calcium and phosphorus in juveniles of the common carp, Cirrkina mri.gaia. Co~piu 1970, 190- 192. Lutz P. L. (l972) Body ~ompartnlentalization and ion distribution in the teleost Perca ,jfwiati/i.~. Camp. Biockem. Physiol. 41A, I81 -193. Lysaya N. M. (1951) Changes in the blood composition of salmon during the spawning migration. IX. /jkhookean. naurhn.-issied. Inst. Rj%. Kkoz. Okeanogr. 35, 47-60. (Quoted by Holmes and Donaldson. 1969). Natochin Y. V. and Lavrova E. A. (1974) The influence of water salinity and stage in life history on ion concentration of fish blood serum. J. Fish Biol. 6, 545555.5. Nicol J. A. C. (1960) Tke Biology of Marine Animuls. Interscience Publishing. New York. Nordlie F. G. and LefBer C. W. (1975) Ionic regulation and the energetics of osmoregulation in MugiL cepkalus Lin. Camp. Biockem. Pkysiol. 51 A, 125 I3 1. Nordlie F. G., Szehstowski W. A. and Nordlie W. C. (1982) Ontogenesis of osmotic regulation in the striped mullet, Mugil cepkalus L. J. Fish Biol. 20, 79-86. Parry G. (1961) Osmotic and ionic changes in blood and muscle of migrating salmonids. .I. esp. &of. 38, 41 i-427.
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Peterson G. L. and Shehadeh Z. H. (197 1) Changes in blood components of the mullet, Mugil cephalus L., following treatment with salmon gonadotropin and methyl testosterone. Comp. Biochem. Physiol. 38B, 451-457. Pickford G. E., Grant F. B. and Umminger B. L. (1969) Studies on the blood serum of the euryhaline cyprinodont fish, Fundulus heteroclitus adapted to fresh or to salt water. Trans. Corm. Acad. Arts Sri. 43, 25-70. Smith H. W. (1929) The composition of the body fluids of the goose fish (Lophius piscatorius). J. biol. Chem. 82, 71-75.
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