590

Resting Metabolic Rate, Critical Swimming Speed, and Routine Activity of the Cyprinodontid, Aphanius dispar, Acclimated to a Wide Range of Salinities

Itai Plaut* salt marshes, intertidal pools, etc.) show physiological adap- Department of Biology, University of Haifa at Oranim, tations that enable them to tolerate and survive extreme salinity Tivon 36006, Israel levels and fluctuations. Most studies on the physiological and behavioral effects of Accepted 6/5/00 euryhalinity and salinity have been done either with a narrow range of salinity, usually subranges between freshwater and full- strength seawater (Igram and Wares 1979; Nelson et al. 1996; Young and Cech 1996; Morgan et al. 1997; Kolok and Sharkey ABSTRACT 1997; Morgan and Iwama 1998; Plaut 1998, 1999a, 1999b; Shi- Specimens of the euryhaline cyprinodontid fish, Aphanius dis- kano and Fujio 1998) or under acute exposures to salinity par, collected in salt ponds, were acclimated to salinities of fluctuations (Davenport and Vahl 1979; Moser and Miller !1 (freshwater), 35 (seawater), 70, 105, and 140 ppt for 4 wk 1994). Data on the effects of long-term acclimation to extreme before measurement of oxygen consumption, critical swim- salinities (above seawater) on fish are rare. Recent studies have ming speed, and routine activity level. Oxygen consumption included only two species, the milkfish, Chanos chanos (Swan- son 1998), and the sheephead minnow, Cyprinodon variegatus , 0.06 ע 0.17 , 0.07 ע was similar in !1, 35, and 70 ppt (0.18 SD ]) but (Haney and Nordlie 1997; Haney et al. 1999). Few fish species ע mL hϪ1 gϪ1, respectively [ mean 0.04 ע and0.16 -mL can tolerate extreme salinity, which may explain the small num 0.2 ע and 0.09 0.02 ע decreased in 105 and 140 ppt (0.12 hϪ1 gϪ1, respectively). Critical swimming speed and routine ber of studies in this area (Nordlie and Haney 1998). activity levels showed the same trend. These results suggest a The cyprinodontid, Aphanius dispar (Teleostei, Cyprinodon- general decrease in physiological function of A. dispar at ex- tidae) is a euryhaline fish species found in a wide range of treme salinities. salinities, from freshwater to 1500% (∼175 ppt) seawater in springs around the Dead Sea and in salt ponds in Atlit, Israel (Lotan 1969, 1971; Lotan and Skadhauge 1972; Skadhauge and Lotan 1974). Lotan (1971) showed that A. dispar is capable of Introduction maintaining its plasma osmotic pressure and ionic concentra- tion when acclimated to salinities from 16 to 105 ppt. However, Teleost fishes are osmoregulators, maintaining their body fluids’ freshwater acclimation reduced A. dispar plasma osmotic pres- osmotic concentration within a relatively narrow range, from sure to 70% (compared with fish in seawater), and acclimation ∼ 260 to 400 mOsmol (Jobling 1995), usually different from the to 140 ppt increased its plasma osmotic pressure to about 135%. osmotic concentration of their environment. To osmoregulate, The ability of A. dispar to tolerate such a wide range of salinities fish actively create a flow of ions and water in the opposite makes it an excellent candidate for studies of salinity effects on direction to the passive flow imposed by the osmotic gradient. other physiological, ecological, and behavioral traits. In addition, they may reduce their gill membrane and/or in- In this study, I examine the effects of extremely high salinity tegument permeability to passive flows. Most fishes are capable on physiological and behavioral functions of A. dispar. I ex- of tolerating only a narrow range of salinities in their natural posed A. dispar to a range of salinities, from freshwater to 175 environment (Haney and Nordlie 1997), and exposure to sa- ppt (500% seawater) for 4 wk, and then measured oxygen linities substantially outside their range may exceed their os- consumption rate, critical swimming speed, and routine activity moregulatory capabilities and reduce their performance (Beam- level. ish 1978; Webb 1994). By contrast, some fishes from habitats characterized by a wide range of salinity fluctuations (estuaries, Material and Methods

*E-mail: [email protected]. Fish Collection, Holding, and Acclimation mm 0.5 ע Physiological and Biochemical Zoology 73(5):590±596. 2000. ᭧ 2000 by The Adult Aphanius dispar (standard length [SL],31.9 ,[SE , range 24.6–46.3 mm], body mass [BM ע University of Chicago. All rights reserved. 1522-2152/2000/7305-0030$03.00 [mean Effects of Wide Salinity Range Acclimation on Aphanius dispar 591 g [range 0.23–1.37]) were collected in the salt surements were performed both before and after the 0.04 ע 0.72 ponds of Atlit, near Haifa, Israel, by hand net. Salinity in the measurements of oxygen consumption of the fish. Each fish salt ponds at the time of collection was ∼57 ppt (∼160% was used only once, and after the measurement, the fish were g) in a preweighed beaker with water and 0.01ע) seawater) and water temperature was 27ЊC. In the laboratory, weighed fish were divided into five groups, each subdivided among transferred to a new aquarium containing “used” fish. three aquaria. These aquaria contained continuously aerated Linear regression analysis of oxygen depletion over time was water from the salt ponds. Fish were treated prophylactically performed for each fish, and the regression coefficient was used for 24 h with malachite green (0.15 ppm) and with methylene to calculate oxygen consumption: blue (1 ppm). Seven percent of the fish died within 3 d of collection; afterward mortality was very low. Two weeks after ˙ Ϫ1 p # # # # Vo22(mmol h ) a 3,600 So V Pa/760, collection, salinity acclimation was begun. Salinity was changed by addition of artificial sea salt (Instant Ocean) or where a is the linear regression coefficient (percentage sϪ1), the by dilution with distilled water. Each day, the salinity was value 3,600 converts seconds to hours, So2 is oxygen concen- increased or decreased by ∼9 ppt. After 14 d, there were five tration at 100% saturation in the experimental salinity at 25ЊC groups in each of five different salinities: freshwater (!1 ppt at an atmospheric pressure of 760 mmHg (Green and Carritt salt), 35, 70, 105, and 140 ppt. Then, fish acclimated to each 1967), V is the water volume in the closed respirometry system salinity were pooled to one larger tank for the rest of the measured specifically for each chamber (L), and Pa is the actual acclimation period (five salinity groups in five tanks). Salin- atmospheric pressure in mmHg. Background (bacterial) oxygen ities were then monitored daily, and distilled water was added consumption measured in the blank chamber was always below accordingly to compensate for evaporation. Fish remained in 4% of the fish’s oxygen consumption measurements. Correc- these salinities for 4 wk before experiments were begun. The tions were made for blank oxygen consumption rates if those aquaria were equipped with biological filters and temperature rates exceeded 1% of the experimental values per run. -1ЊC), and fish were fed twice a day with Teעcontrol (25Њ tramin flakes and live Daphnia magna and Artemia salina. Critical Swimming Speed (Ucrit) Swimming performance was measured as critical swimming Oxygen Consumption Measurements speed (Ucrit) in a water tunnel described in Plaut (2000). Post- The respirometer used in this study was described in detail in absorptive fish (24 h) were placed in the water tunnel con- Plaut (1999a, 1999b). This is a semiclosed respirometer (Stef- taining the relevant water salinity at a temperature of 0.5ЊC. Water velocity was set to 4 cm sϪ1 (about 1 SLעfensen 1989) with eight measuring cells. Water was directed 25Њ Ϫ1 from an aerated (100% O2 saturation), temperature-controlled s ), and the fish were left undisturbed for 2 h to recover reservoir containing water at the experimental salinity to the from handling (Kolok 1991; Peake et al. 1997). Water velocity respirometer chamber and back to the reservoir by peristaltic was then increased in increments of 4 cm sϪ1 at 5-min in- pumps via c-flex tubing. Three-way stopcocks made it possible tervals, until the fish fatigued. Fatigue was determined as the to disconnect a chamber from the reservoir and to direct the situation where the fish could no longer maintain position water flow from the respirometer chamber to a cell with an against the current and were swept downstream and held oxygen electrode and back to the chamber in closed circulation. against the mesh screen at the downstream end of the water

Thus, oxygen depletion in the chamber could be measured tunnel. Ucrit was calculated according to the equation (Brett without disturbance to the fish. 1964) Fish were not fed for 24 h before measurement. Postab- p ϩ sorptive fish were placed in each of seven chambers (one cham- Ucrit Uiiiiii[U (T /T )], ber was left empty as a blank control) and left for 4–5 h to recover from handling. Preliminary tests showed that oxygen where Ui is the highest velocity maintained for the whole 5 Ϫ1 Ϫ1 consumption was high immediately after placement of the fish min (cm s ), Uii is the velocity increment (i.e., 4 cm s ), Ti in the chambers and then decreased to a stable value after is the time elapsed at fatigue velocity (min), and Tii is the approximately 2 h and remained stable for more than 24 h. At interval time (5 min). Ucrit’s were calculated both as absolute the beginning of the measurement, fish were completely qui- (cm sϪ1) and relative (SL sϪ1) swimming speeds. escent in the chamber, so the oxygen consumption rates are regarded as resting metabolic rate (RMR). Following the re- Routine Activity Rate covery period, oxygen consumption was measured over about 15 min, long enough to detect depletion of oxygen concentra- Routine activity rates of A. dispar were measured in five isolated tion in the water (15% decrease of saturation). Oxygen satu- identical aquaria,28 # 14 # 18 cm (length, width, and height, ration was not allowed to decrease below 85%. Blank mea- respectively), containing water with the relevant salinity of the 592 I. Plaut

.1Њ C under photoperiods of 12L : 12Dעtested group at25Њ Ten (two for each aquarium) infrared beam projectors and recording photocells were placed along the long wall of the aquarium opposite a reflector. Photocells were placed in one- third and two-thirds of the aquaria length (9 cm from each other), 6 cm above the bottom. A counter connected to a recorder attached to a PC recorded every time a fish crossed a beam. The computer recorded the accumulated crosses for each photocell every 15 min. Because A. dispar is a gregarious species, activity levels were measured in groups of six fish for each salinity. A group of six fish, acclimated to a certain salinity, was placed in one aquarium for 72 h before measurement. After about 60 h, aquaria were inspected to ensure that all fish were in good condition and behaving normally. Measuring began 12 h after the experi- SE ) of Aphanius dispar at ע menter left the room and continued for 24 h. Five sets of Figure 1. Oxygen consumption (mean measurements were taken, each with different fish. Data for different salinities. Data with different letters are significantly different each group (salinity) for the five sets were assembled for each ().P ! 0.05 hour of the day (24 h) for analysis. 0.004), but no body size effect was detected at other salinities. Ϫ1 Relative swimming speeds (Ucrit measured as SL s ) decreased Statistical Analyses significantly as body size increased for fish in all salinities (Table Resting oxygen consumption was compared among salinities 1; Fig. 2). The slopes were homogeneous among groups p p using ANOVA and the Tukey’s post hoc test. Relative critical (,).F4,78 0.272 P 0.895 Ucrit of fish acclimated to freshwater, Ϫ1 35 ppt, and 70 ppt did not differ (ANCOVA). However, U swimming speed (Ucrit,SLs ) values were plotted against stan- crit dard lengths of the fish. Regression lines were tested for ho- was lower in fish acclimated to 105 ppt. It decreased further mogeneity of slopes, and since all were found homogeneous, in fish acclimated to 140 ppt. Several fish acclimated to 140 ANCOVA was performed. Because ANCOVA detected signifi- ppt did not survive the tests, so the experiments of this group cant differences between salinities, a Tukey’s HSD multiple were limited to a sample size of seven fish only. comparison was conducted to test for differences between each pair of salinity (Wilkinson 1990). Activity data were compared among the different salinities Routine Activity Rate for each hour of the day using ANOVA and Tukey’s post hoc Aphanius dispar showed a striked circadian rhythm, being active test. Differences were considered significant atP ! 0.05 . during the light period and relatively quiescent during the dark period (Fig. 3). Fish acclimated to freshwater, 35 ppt, and 70 Results ppt showed similar rates of activity in light and dark periods Oxygen Consumption (data compared for each hour of the day by ANOVA and Tukey’s post hoc test). In some hours, one of these groups was Oxygen consumption rate is expected to be strongly influenced significantly more, or less, active than the others, but no clear by body size (Haney and Nordlie 1997). However, no size effects pattern could be detected. However, activity was lower in fish were detected, which probably reflects the small size range of acclimated to 105 and 140 ppt, and during some hours, fish the fish examined. Resting oxygen consumption of Aphanius acclimated to 140 ppt were significantly less active than those dispar did not differ among fish held in freshwater, 35 ppt, and acclimated to 105 ppt. n p 14 ], and] 0.06 ע n p 22 ], 0.17] 0.07 ע ppt (0.18 70 -n p 24 ] mL hϪ1 gϪ1, respectively). However, ox] 0.04 ע 0.16 Discussion ygen consumption was lower for fish held in 105 and 140 ppt n p 20 ] mL hϪ1 gϪ1, Although Aphanius dispar inhabits water bodies of wide salinity] 0.02 ע n p 20 ] and 0.09] 0.02 ע 0.12) respectively; Fig. 1). range (Lotan and Skadhauge 1972; Skadhauge and Lotan 1974), it performs best at salinities between freshwater and 70 ppt, and its performance significantly decreases when salinity in- Critical Swimming Speed creases above 70 ppt. This decrease is demonstrated both at Absolute (cm sϪ1) critical swimming speed of fish in freshwater the physiological level (RMR) and the functional-ecological 2 p p p increased with body size (SL;R 0.35 ,F1, 19 10.4 , P level (swimming performance and routine activity level). The Effects of Wide Salinity Range Acclimation on Aphanius dispar 593 pattern observed for A. dispar is in agreement with the study of Haney et al. (1999) on the sheephead minnow. Extreme salinities may be stressful for salt marsh resident fishes, resulting in reduced energy expediencies. RMR of A. dispar was not affected by salinity acclimation of freshwater, 35 ppt, and 70 ppt but decreased when acclimated to salinities above 70 ppt. Most studies on effects of salinity on metabolic rate of fishes have measured either the effects of acute exposure to different salinities (Davenport and Vahl 1979; von Oertzen 1984; Moser and Miller 1994) or salinity effects on fish that can tolerate only a narrow range of salinity with no obvious euryhaline adaptation (Stuenkel and Hillyard 1981; Meador and Kelso 1989, 1990). Moreover, most of these studies tested salinities within the ranges between freshwater and sea- water only (see also Plaut 1999a, 1999b). Thus, data on the effects of long-term acclimation to a wide range of salinity on fish’s metabolic rate are few. Several studies have demonstrated Figure 2. Relative critical swimming speed (Ucrit)ofAphanius dispar an increase in metabolic rate in fish with an increase in the acclimated to different salinities, in relation to fish standard length difference between ambient salinity and isosmotic concentra- (SL). Filled circles, freshwater; open circles, 35 ppt; filled squares, 70 ppt; tion, which may reflect an elevation in the cost of osmoregu- open squares, 105 ppt; filled triangles, 140 ppt. lation (Febry and Lutz 1987; Ku¨ltz et al. 1992; Morgan et al. 1997). However, other studies have reported a decrease in met- 70 ppt, but increased in 105 ppt, while other osmoregulatory abolic rate of euryhaline fishes as salinity increased. This trend factors, such as plasma osmolarity and ClϪ concentration, pro- was shown in the salt marsh fish, Cyprinodon variegatus, ac- gressively increased as ambient salinity increased. Considering climated to salinity above 40 ppt (Nordlie et al. 1991; Haney these data, it is not clear to what extent A. dispar is an os- and Nordlie 1997; Haney et al. 1999), in the freshwater blenny, moregulator or osmoconformer, but in the case of Naϩ con- Salaria fluviatilis, acclimated to 14 and 35 ppt (Plaut 1999a), centration it seems to be comparable to C. variegatus. Thus, and in the milkfish, Chanos chanos, acclimated to 55 ppt (Swan- these data support the suggestion that reduction in gill son 1998). membrane and/or integument permeability helps to decrease Nordlie et al. (1991) and Haney and Nordlie (1997) suggested ionic influx but reduces the ability of the fish to obtain oxygen that the decrease in oxygen consumption observed at extremely from the water (Kristensen and Skadhauge 1974; Davenport high salinity is related to permeability changes of the gill and Sayer 1993; Haney and Nordlie 1997). Reduction in gill membrane and/or the integument. Haney and Nordlie (1997) and opercular membrane permeability as a result of extreme compared the salinity effects on oxygen consumption and crit- osmotic conditions has been shown for several fish species ical oxygen tension with data from Nordlie (1985) and showed (Karnaky et al. 1976; Ku¨ltz and Onken 1993; Bindon et al. that the point at which oxygen consumption is reduced cor- 1994a, 1994b). Swanson (1998) reported that the milkfish, C. responds well to a diminished ability of C. variegatus to os- chanos, acclimated to 35 ppt, consumed more oxygen than it moregulate efficiently. Lotan (1971) reported that in A. dispar, did under acclimation to both 15 ppt (close to isosmotic con- Naϩ concentration in the plasma was stable between 14 and centration) and 55 ppt. However, acclimation to 55 ppt resulted

Table 1: Linear regression between body size (SL, mm, independent Ϫ1 variable) and relative critical swimming speed (Ucrit,SLs , dependent variable) of Aphanius dispar acclimated to different salinities Salinity (ppt) n Linear Regression Equation R2 P Value ! ע Ϫ ע p A ! 1 ...... 21 Ucrit 16.03 ( .96) .19( .03)SL .709 .001 ! ע Ϫ ע p A 35 ...... 20 Ucrit 15.87 ( 1.11) .21( .03)SL .691 .001 ! ע Ϫ ע p A 70 ...... 22 Ucrit 16.15 ( 1.38) .21( .04)SL .548 .001 ! ע Ϫ ע p B 105 ...... 18 Ucrit 14.15 ( .80) .21( .02)SL .830 .001 ע Ϫ ע p C 140 ...... 7 Ucrit 12.28 ( 1.05) .18( .03)SL .864 .002 Note. Intercept values with different superscript letters are significantly different. 594 I. Plaut

Figure 3. Daily routine activity rate of Aphanius dispar acclimated to different salinities in a significant decrease in metabolic rate. In this case, the review of swimming capacity, mentioned only three studies. increase of metabolic rate at 35 ppt acclimation in comparison Two dealt with ontogenetic salinity adaptation in salmonids with 15 ppt may be explained as an increase of osmoregulatory (Alderdice 1963; Glova and McInnerney 1977), and one re- cost, but the decrease at 55 ppt acclimation in comparison with ported no significant effects on skipjack and yellowfin tuna 35 ppt may be a result of decreased permeability of the gill exposed to a narrow salinity range of 29–34 ppt (Dizon 1977). membrane and/or integument. Nelson et al. (1996) exposed Gadus morhua acclimated to 31–20

If the reduction in oxygen consumption occurs as a result ppt and vice versa and found no effects on Ucrit, but this is a of gill membrane and/or integument permeability, such a de- very narrow range compared with the salinity range tested in crease should be observed whenever a fish experiences salinity this study. Kolok and Sharkey (1997) measured Ucrit of the beyond its osmoregulatory capability. When a marine fish is euryhaline gulf killifish, Fundulus grandis, acclimated to fresh- exposed to salinities below its body fluid osmotic concentration, water (∼1 ppt) and brackish water (∼12 ppt) and showed that to maintain its osmotic balance it should reverse the direction Ucrit of fish acclimated to brackish water was faster than that of its active osmotic flow. Instead of excreting ions, it should of fish acclimated to freshwater. Kolok and Sharkey (1997) absorb them from the seawater, and instead of keeping water attributed the decrease of Ucrit in fish acclimated to freshwater in its body, it should get rid of excess water. Since most marine to the increase of metabolic cost of compared fishes are limited in their ability to reverse the direction of with fish in brackish, close to isosmotic water; thus, the ad- osmotic flows, they may drastically reduce their gill membrane ditional cost of osmoregulation is met at the expense of oxygen and integument permeability to ions and water, an action that available for aerobic swimming. However, this may also be a will result in reducing the permeability to oxygen as well. result of reduced gill membrane and integument permeability Such a phenomenon was observed in two species of marine because of the increasing difference in osmotic pressure be- blennies acclimated to freshwater. In the marine peacock tween body fluids and the environment. Swanson (1998) found blenny, Salaria pavo, long-term acclimation to 14 ppt did not that Ucrit of milkfish decreased as salinity increased. In light of affect its oxygen consumption, but long-term acclimation to Swanson’s (1998) metabolic rate data mentioned above, these freshwater reduced its metabolic rate (Plaut 1999a). A similar results may be an expression of the effects of both osmoreg- phenomenon was reported for the intertidal blenny, Parablen- ulation cost (at 35 ppt) and decrease of permeability of the gill nius sanguinolentus (Plaut 1999b). These results support the membrane/integument (at 55 ppt). low-permeability hypothesis, which may be true also in the case In this study, Ucrit show the same trend as RMR. It seems of fishes in an extreme hyposaline environment. that the decrease in the ability to obtain oxygen from the water

Studies on the effects of salinity acclimation on swimming limited the aerobic ability of the fish and thus decreased Ucrit performance of fish are few. Beamish (1978), in his extensive at high salinities. Effects of Wide Salinity Range Acclimation on Aphanius dispar 595

Activity levels of A. dispar were high when fish were accli- Dizon A.E. 1977. Effect of dissolved oxygen concentration and mated to freshwater, 35 ppt, and 70 ppt and progressively de- salinity on swimming speed of two species of tunas. Fish creased in fish acclimated to 105 and 140 ppt. This pattern was Bull 75:649–653. observed in both light and dark phases. This trend is consistent Febry R. and P. Lutz. 1987. Energy partitioning in fish: the with the findings in RMR and Ucrit measurement and with Plaut activity-related cost of osmoregulation in a euryhaline cich- (2000). lid. J Exp Biol 128:68–85. The overall picture that emerges in this study is that although Glova G.J. and J.E. McInerney. 1977. Critical swimming speeds A. dispar is found in an extremely wide range of salinities, when of coho salmon (Oncorhynchus kisutch) fry to smolt stages the fish are exposed to salinities above 70 ppt their overall in relation to salinity and temperature. J Fish Res Board Can performance significantly decreases. This phenomenon is likely 34:151–154. to have substantial ecological effects on A. dispar populations Green E.J. and D.F. Carritt. 1967. New tables for oxygen sat- in extremely saline habitats. Decreases in metabolic rate, swim- uration. J Mar Res 25:140–147. ming capacity, and activity rate are expected to reduce the Haney D.C. and F.G. Nordlie. 1997. Influence of environmental ability of the fish to prey, to avoid predation, and to perform salinity on routine metabolic rate and critical oxygen tension other functions that are critical to ensure survival. The fact that of Cyprinodon variegatus. Physiol Zool 70:511–518. A. dispar regularly inhabits such habitats is probably because Haney D.C., F.G. Nordlie, and J. Binello. 1999. Influence of its competitors and predators cannot tolerate such physical simulated tidal changes in ambient salinity on routine met- conditions of extreme salinity that may compensate for de- abolic rate in Cyprinodon variegatus. Copeia 1999:509–514. creased performance. Igram R. and W.D. Wares II. 1979. Oxygen consumption in the fathead minnow (Pimephales promelas Rafinesque). II. Effects of pH, osmotic pressure and light level. Comp Acknowledgments Biochem Physiol 62A:895–897. Jobling M. 1995. Environmental Biology of Fishes. Chapman I wish to thank Dr. A. Israel for his assistance in fish collection, & Hall, London. T. Weihs for technical assistance during the experimental phase, Karnaky K.J., Jr., S.A. Ernst, and C.W. Philpott. 1976. Teleost and Prof. F. G. Nordlie for his helpful comments on the man- chloride cell. I. Response of pupfish Cyprinodon variegatus uscript. This study was supported, in part, by a research grant gill Na K-ATPase and chloride cell fine structure to various from the Institute for the Kibbutz Research, Oranim. high salinity environments. J Cell Biol 70:144–156. Kolok A.S. 1991. Photoperiod alters the critical swimming Literature Cited speed of juvenile largemouth bass, Micropterus salmoides, acclimated to cold water. Copeia 1991:1085–1090. Alderdice D.F. 1963. Some Effects of Simultaneous Variation Kolok A.S. and D. Sharkey. 1997. Effect of freshwater accli- in Salinity, Temperature and Dissolved Oxygen on the Re- mation on the swimming performance and plasma osmo- sistance of Juvenile Coho Salmon (Oncorhynchus kisutch)to larity of the euryhaline gulf killifish. Trans Am Fish Soc 126: a Toxic Substance. PhD thesis. University of Toronto. 866–870. Beamish F.W.H. 1978. Swimming capacity. Pp. 101–187 in W.S. Kristensen K. and E. Skadhauge. 1974. Flow along the gut and Hoar and J.D. Randall, eds. . Academic Press, intestinal absorption of salt and water in euryhaline teleosts: New York. a theoretical analysis. J Exp Biol 60:557–566. Bindon S.D., J.C. Fenwick, and S.F. Perry. 1994a. Branchial Ku¨ltz D., R. Bastrop, K. Ju¨rss, and D. Siebers. 1992. Mito- chloride cell proliferation in the rainbow trout, Oncorhyn- chondria-rich (MR) cells and the activities of Naϩ/Kϩ-ATP- chus mykiss: implications for gas transfer. Can J Zool 72: ase and carbonic anhydrase in gill and opercular epithelium 1395–1402. of O. mossambicus adapted to various salinities. Comp Bindon S.D., K.M. Gilmour, J.C. Fenwick, and S.F. Perry. 1994b. Biochem Physiol 102B:293–301. The effects of branchial chloride cell proliferation on res- Ku¨ltz D. and H. Onken. 1993. Long-term acclimation of the piratory function in the rainbow trout Oncorhynchus mykiss. teleost Oreochromis mossambicus to various salinities: two J Exp Biol 197:47–63. different strategies in mastering hypertonic stress. Mar Biol Brett J.R. 1964. The respiratory metabolism and swimming 117:527–533. performance of young sockeye salmon. J Fish Res Board Can Lotan R. 1969. Sodium, chloride and in the eu- 21:1183–1226. ryhaline teleost Aphanius dispar (Ruppell) (Cyprinodonti- Davenport J. and M.D.J. Sayer. 1993. Physiological determi- dae). Z Vgl Physiol 65:455–462. nations of distribution in fish. J Fish Biol 43:121–145. ———. 1971. Osmotic adjustment in the euryhaline teleost Davenport J. and O. Vahl. 1979. Responses of the fish Blennius Aphanius dispar (Cyprinodontidae). Z Vgl Physiol 75: pholis to fluctuating salinities. Mar Ecol Prog Ser 1:101–107. 383–387. 596 I. Plaut

Lotan R. and E. Skadhauge. 1972. Intestinal salt and water ———. 1999a. Effects of salinity acclimation on oxygen con- transport in a euryhaline teleost, Aphanius dispar (Cypri- sumption in the freshwater blenny, Salaria fluviatilis, and the nodontidae). Comp Biochem Physiol 42A:303–310. marine peacock blenny, S. pavo. Mar Freshw Res 50:655–659. Meador M.R. and W.E. Kelso. 1989. Behavior and movement ———. 1999b. Effects of salinity on survival, osmoregulation, of largemouth bass in response to salinity. Trans Am Fish and oxygen consumption in the intertidal blenny, Parablen- Soc 118:409–415. nius sanguinolentus. Copeia 1999:775–779. ———. 1990. Physiological responses of largemouth bass, Mi- ———. 2000. Effects of fin size on swimming performance, cropterus salmoides, exposed to salinity. Can J Fish Aquat Sci swimming behaviour and routine activity of zebrafish Danio 47:2358–2363. rerio. J Exp Biol 203:813–820. Morgan J.D. and G.K. Iwama. 1998. Salinity effects on oxygen Shikano T. and Y. Fujio. 1998. Relationships of salinity tolerance consumption, gill Naϩ,Kϩ-ATPase and ion regulation in ju- to immunolocalization of Naϩ,Kϩ-ATPase in the gill epi- venile coho salmon. J Fish Biol 53:1110–1119. thelium during seawater and freshwater adaptation of the Morgan J.D., J.M. Wilson, and G.K. Iwama. 1997. Oxygen con- guppy, Poecilia reticulata. Zool Sci 15:35–41. sumption and Naϩ,Kϩ-ATPase activity of rectal gland and Skadhauge E. and R. Lotan. 1974. Drinking rate and oxygen gill tissue in the spiny dogfish, Squalus acanthias. Can J Zool consumption in the euryhaline teleost Aphanius dispar in 75:820–825. waters of high salinity. J Exp Biol 60:547–556. Moser M.L. and J.M. Miller. 1994. Effects of salinity fluctuation Steffensen J.F. 1989. Some errors in respiratory of aquatic on routine metabolism of juveniles pot, Leiostomus xanthu- breathers: how to avoid and correct for them. Fish Physiol rus. J Fish Biol 45:335–340. Biochem 6:49–59. Nelson J.A., Y. Tang, and R.G. Boutilier. 1996. The effects of Stuenkel E.I. and S.D. Hillyard. 1981. The effects of temperature salinity change on the exercise performance of two Atlantic and salinity acclimation on metabolic rate and osmoregu- cod (Gadus morhua) populations inhabiting different envi- lation in the pupfish Cyprinodon salinus. Copeia 1981: ronments. J Exp Biol 199:1295–1309. 411–417. Nordlie F.G. 1985. Osmotic regulation in the sheephead min- Swanson C. 1998. Interactive effects of salinity on metabolic now Cyprinodon veriegatus Lacepe`de. J Fish Biol 26:161–170. rate, activity, growth and osmoregulation in the euryhaline Nordlie F.G. and D.C. Haney. 1998. Adaptations in salt marsh milkfish (Chanos chanos). J Exp Biol 201:3355–3366. teleosts to life in waters of varying salinity. Ital J Zool 65:S- von Oertzen J.-A. 1984. Influence of steady-state and fluctu- 409. ating salinities on the oxygen consumption and activity of Nordlie F.G., S.J. Walsh, D.C. Haney, and T.F. Nordlie. 1991. some brackish water shrimps and fishes. J Exp Mar Biol Ecol The influence of ambient salinity on routine metabolism in 80:29–46. the teleost Cyprinodon variegatus Lacepe`de. J Fish Biol 38: Webb P.W. 1994. The biology of fish swimming. Pp. 45–62 in 115–122. L. Maddock, Q. Bone, and J.M.V. Rayner, eds. Mechanics Peake S., C. Barth, and R.S. Mckinley. 1997. Effect of recovery and Physiology of Swimming. Cambridge University parameters on critical swimming speed of juvenile rainbow Press, Cambridge. trout (Oncorhynchus mykiss). Can J Zool 75:1724–1727. Wilkinson L. 1990. SYSTAT: the system for statistics. SYSTAT, Plaut I. 1998. Comparison of salinity tolerance and osmoreg- Evanston, Ill. ulation in two closely related species of blennies from dif- Young P.S. and J.J. Cech. 1996. Environmental tolerances and ferent habitats. Fish Physiol Biochem 19:181–188. requirements of splittail. Trans Am Fish Soc 125:664–678.