The effects of hypercapnia on the growth of juvenile white sturgeon, Acipenser transmontanus

Aquaculture ELSEVIER

Aquaculture 147 (1996) 293-299

The effects of hypercapnia on the growth of juvenile white sturgeon, Acipenser transmontanus Carlos E. Cracker Department

*, Joseph J. Cech Jr.

ofWildlife, Fish, and Conseroation Biology, University ofCalijiwnia, Davis, CA 95616, USA Accepted 1 August 1996

Abstract Environmental hypercapnia (high dissolved [CO,D results from high-density sturgeon culture in systems using 0, injection and water re-use. The influence of environmental hypercapnia on the growth of the juvenile white sturgeon, Acipenser frunsmontanus, (fish initial wet weight, about 4 g) was examined by exposing the fish to different CO, concentrations in replicate, flow-through aquaria under normoxic conditions (oxygen tension, above 130 ton PO,> at 19°C. The fish were fed ad libitum rations of commercial trout pellets (Silvercup). After 28 days exposure to severe hypercapnia ([CO,], 45-75 mg 1-l; pH 7.01, growth was significantly reduced (P < 0.05) (the final body weight was reduced by about 38%; the specific growth rate (SGR), 1.17) compared to that of sturgeon in normocapnic water ([CO,], 0.52 mg 1-l; pH 8.0; SGR, 2.86), presumably due to decreased food consumption. In two subsequent experiments (initial wet weights, approximately 1 and 3 g). a low water pH (a mean of 7.1, via HCl addition to water) did not significantly affect the growth. Keywords: Growth; Hypercapnia; Sturgeon; Acipemer;

~0,

1. Introduction Interest in the intensive commercial production of white sturgeon arose in 197Os, because of the sturgeon’s rapid growth and high feed efficiency under hatchery conditions (Hung et al., 1989). Aquaculture facilities that incorporate injection and water re-use maintain a high dissolved LO,], but may also have

the late certain oxygen a water

* Corresponding author. Tel.:(916)752-8659; fax.: (9161752-4154; e-mail: [email protected]. 00448486/96/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved. PII SOO44-8486(96)0141 I-1

294

C.E. Cracker. J.J. Cech, Jr./Aquaculture

147 (1996) 293-299

[CO,] above 45 mg 1-l (Cracker and Cech, unpublished data). Under these conditions, reductions in the growth rates of sturgeon have been observed (Jim Michaels, Elverta, CA, personal communication). In culture, high stocking densities result in high CO, tensions (hypercapnia). CO, is a metabolic byproduct of aerobic respiration and when the water [CO,] is high, CO, accumulates within the animal (Heisler, 1986). Consequently, the arterial pH decreases due to the increase in arterial Pco, and its subsequent hydration to carbonic acid and liberation of Ht. Blood acid-base and respiratory disturbances associated with shortand long-term exposure to hypercapnia have been investigated in several fish species (Eddy et al., 1977; Toews et al., 1983; Claiborne and Heisler, 1986; Cracker and Cech, unpublished results), but the effects of high [CO,] on growth have not been studied previously. The primary objective of this study was to measure the growth rates of juvenile white sturgeon, Acipenser transmontanus, during prolonged, sublethal, hypercapnic exposure (dissolved [CO,], 45-75 mg 1-l >. A high water [CO,] lowers the water pH due to the hydration of CO, to H,CO,, which partially dissociates and liberates H+. Thus, a secondary objective was to investigate whether possible effects on the growth resulted from increased CO, or from lowered pH alone.

2. Materials

and methods

Prior to use in the experiments, sibling juvenile white sturgeon, Acipenser transmontunus, were reared at the University of California, Davis (UCD) Aquaculture and Fisheries Program Facility in a 2 m diameter tank receiving a continuous supply of unchlorinated well water at 19” f 1.0 C. The fish were fed l-3 times daily with commercial trout feed (Silvercup, Murray UT, USA) and were kept under a natural photoperiod (14L: lOD>. Three experiments were performed (on young-of-the-year white sturgeon) between August 1994 and August 1995. For each experiment, 80 fish were starved for 24 h and then randomly divided into eight groups (four controls and four test) with ten in each. The fish were individually weighed (fO.O1 g> with an Ohaus B 3000D electronic balance using the method described by Cech et al. (19841, and placed into 38 1, rectangular glass aquaria equipped with a standpipe and continuously supplied with well-water. The mean total alkalinity and the total hardness of the source water for all three experiments were 282 + 16 mg 1-l and 288 & 12 mgg ‘, respectively (Paul Lutes, UC Davis, personal communication). The water flow through the aquaria was maintained at approximately 0.45 1 min-’ and the dissolved 0, content was always more than 90% of air saturation. Diffuser stones placed in each aquarium ensured that the water was well mixed. In each aquarium, the fill time and 99% washout time approximated 1.5 h and 6.5 h, respectively. The fish were fed ad libitnm, food being provided at least three times daily (Silvercup trout pellets). Fecal material and uneaten food were siphoned from the aquaria at least three times daily. The feed rations provided were adjusted periodically based on food acceptance and the amount of uneaten food left in the aquaria.

C.E. Cracker, JJ. Cech, Jr./Aquaculture

2.1. Experiment

147 (1996) 293-299

295

I

The test fish (initial mean wet weight, 4.03 * 0.7 g) were chronically (28 days) subjected to hypercapnic water conditions ([CO,], 45-75 mg 1-l). The water [CO,] was maintained by continuous, regulated, injection of a 10% CO,/90% air mixture into the aquaria1 water (Sierra Airgas Co., Sacramento, CA.) through the diffuser stones. The control aquaria received air injections via the diffuser stones. 2.2. Experiment

2

All the fish (initial mean wet weight, 1.16 4 0.2 g) were subjected to normocapnic water (for 28 days) while the test aquaria received a continuous HCl drip. The acid drip was prepared by diluting 6.0 N HCI into well-water (1:200) in a large, 180 1, polyethylene (Nalgene) tank (pH 2.0). The mixture was pumped to a constant-head 20 1 reservoir, located above the experimental set-up, and was gravity-delivered to the respective aquaria via clear, vinyl tubing (Tygon) regulated by Teflon stopcocks. The drip rates were matched for all test aquaria (100 drops min- ’ ), and the resulting pH ( f 0.1 pH unit) matched that under hypercapnic conditions. 2.3. Experiment

3

This protocol was identical to that for experiment 2, except that the initial weights (3.26 + 0.6 g) more closely matched those of experiment 1. 2.4. Analytical

fish

procedures

The water quality variables were measured daily. The water pH and temperature were measured with a calibrated, hand-held meter (Corning PS-1.5) and a mercury thermometer, respectively. The water [NH,] was measured with an ammonia nitrogen test kit (Hach, model Nl-81, and dissolved gas tensions (PO, and Pco,) were measured using a calibrated meter and thermostatted electrodes (Radiometer PHM73/E5046/D616 and E5036/D616, respectively). The PO, (torr) data were transformed to dissolved 0, (mg I-’ > using a nomogram (Green and Carritt, 1967). The Pco, (ton-) data were transformed to dissolved CO, (mg I- ’ > using a temperature- and salinity-corrected CO, solubility table (Boutilier et al., 1984). 2.5. Growth measurements After 28 days, each reweighing them. Final control groups. Specific percentage body weight SGR = lOO(lnW,

experiment was terminated by starving the fish for 24 h and weights were used to compare growth between the test and the growth rates (SGR; Ricker, 1979) were calculated in units of per day from - lnW,)t-’

(where W, is the mean initial wet weight (g), W, is the mean final weight (g), and t is

296

C.E. Cracker, J.J. Cech, Jr./Aquaculture

the duration of the experiment growth experiments.

147 (1996) 293-299

(days)) in order to facilitate

comparisons

with other fish

2.6. Statistical analyses Initial mean body weights and final weights (growth) between treatment groups were compared by use of t-tests. Comparisons of growth, dissolved O,, dissolved CO,, temperature, and pH, were analyzed using one-way ANOVA (all experiments) or t-tests (within each experiment) using SigmaStat statistical software. All values are reported as the mean plus or minus one standard deviation (SD), and 0.05 was used as the criterion for significance.

3. Results

Water quality parameters were similar among the experiments; dissolved 0, was always greater than 90% of air saturation in all aquaria (Table l), the temperature was relatively constant (grand mean, 19.1 + 0.2 “C), and the water total ammonia concentration was always less than 0.2 ppm (sensitivity limit of the test kit). In experiment 1, the hypercapnic aquaria had significantly (P < 0.05) higher CO, concentrations and significantly (P < 0.05) lower water pH values than the controls (Table 1). The growth of the sturgeon was suppressed in the hypercapnic treatment groups (experiment 1, Table 1). While fish in the control (normocapnic) aquaria exhibited typical feeding behavior, i.e. taking pellets off the bottom, fish in the hypercapnic aquaria swam erratically and foraged less persistently.

Table 1 Water quality variables, 28 days a

initial and final live body weights,

Parameter

Experiment

1

and specific growth rates for white sturgeon over

Experiment

2

Experiment Control

3 Test

Control

Test

Control

Test

nb Initial mass (g) Temp. (“0 Ka1 (mg 1-t)

40 4.03 If:0.7 19.3+0.0 9.01tO.l 7.8 + 0.0

40 4.01 -t 0.6 19.3*0.0 7.OkO.l 8.9f0.5 *

40 1.16~kO.2 18.9 rt 0.0 8.8 *O.O 8.1 f 0.0

40 40 1.14k0.2 3.26 f 0.6 18.9 f 0.0 19.1 *o.o 7.1 8.9 *o.o k 0.0 * 8.0fO.O 8.7+0.1

30 3.25 + 0.4 19.1&-0.0 7.1 8.850.1 fO.O *

[CO,1 (mg l- ‘)

0.52+0.0 31 8.99f4.3 2.86

42k2.4 * 34 5.57f2.1 ’ 1.17

0.52 * 0.0 31 2.44 f 0.2 2.65

0.52 + 0.0 33 2.28 f 0.5 2.47

0.52 + 0.0 20 5.39+ 1.0 1.80

nc Final mass (g) SGR (% body wt. per day)

a Data are the grand mean k SD computed from replicate denoted by asterisks are significantly different (P < 0.05; b The number of fish in all the 3-4 replicate aquaria, per ’ The number of fish in all the 3-4 replicate aquaria, per

0.52 * 0.0 31 6.80+0.9 2.63

means. For each experiment, data in the same row t-test). treatment group, at the start of the experiment. treatment group, at the end of each experiment.

C.E. Cracker. J.J. Cech, Jr./Aquaculture

I47 (1996) 293-299

297

The growth of all sturgeon during the normocapnic, “low-pH” experiments was positive. There was no significant difference between the final weights of the control and the test fish (P > O.OS>, in either experiment 2 or experiment 3 (Table l), indicating no effect of decreased pH on growth. During experiment 3, only 30 test fish completed the growth trial, because 10 fish died when a tank water inflow tube was dislodged from its supporting bracket and the acid continued to drip into the tank. All other mortalities (17% of all fish used for experiments 1, 2, and 3) were apparently due to starvation; the dead fish had no food in the gut, but some (50%) had gas trapped in the gut (“floaters”). The floaters were unable to forage efficiently and eventually died. Post-mortem, X-ray analysis revealed gastro-intestinal air emboli.

4. Discussion The growth of juvenile white sturgeon was significantly decreased by environmental hypercapnia that simulated conditions in high-density sturgeon culture tanks employing oxygen injection. In our study, control fish had the expected growth of fish this size; they doubled their body weight in four weeks (Cech et al., 1984; Hung et al., 1993). The growth of the fish exposed to hypercapnia was, however, severely suppressed (Table 1). This supports the view that the decreased growth in the hypercapnic tanks was due to the high CO, content/neutral pH conditions existing there. During the experiments, water flow through the aquaria remained high, and the water total ammonia in all aquaria remained undetectable, suggesting that any ammonia effects on growth were insignificant compared to the measured CO, effects. High [CO,] has previously been shown to cause a decreased growth rate in fish. In chronic exposure (330 days), high environmental [CO,] (50-60 mg 1-l; pH 6.15-6.30) resulted in a decreased growth of rainbow trout (Oncorhynchus mykiss) and renal and enteric histopathology (Smart et al., 1979). Hypercapnia ([CO,], 25 mg 1-l) increases the susceptibility to bacterial infections, causes CO, anesthesia, and affects oxygen use in channel catfish, Zcrulurus puncrulus (Plumb, 1984). In our study, the reduced growth rates of the hypercapnic fish were apparently due to CO,-induced changes in feeding behavior. Hypercapnic fish appeared to spend much less time foraging than normocapnic fish, which continuously skimmed the tank bottoms for food. Respiratory acidosis, a condition which is manifested in fish subjected to hypercapnia (Eddy et al., 1977; Toews et al., 1983; Claibome and Heisler, 1986; Cracker and Cech, unpublished results) may have caused a nonspecific, chronic, metabolic stress. Eddy et al. (1979) chronically exposed rainbow trout to high [CO, I and showed that the fish suffered from an uncompensated respiratory acidosis. The elevated plasma [H+] causes decreased hemoglobin-O, binding (Bohr and Root effects), which contributes significantly to reduced arterial 0, concentrations despite high environmental 0, partial pressures (P,,) (Packer, 1979; Ultsch et al., 1981; Randall and Brauner, 1991). This type of physiological stress may have resulted in the fish reducing their foraging activity, thereby decreasing feeding and growth. Because it is possible that the observed differences in the growth rates may have

298

C.E. Cracker, J.J. Cech, Jr./Aquaculrure

147 (1996) 293-299

resulted from changes in pH and not hypercapnia per se, the influence of reduced pH on growth was also examined. In farm-raised channel catfish, Zctulurus punctutus, disturbances in respiration, osmoregulation, and blood pH/acid-base balance result from exposure to low water pH levels (high water [H’]) which reduce growth, reproduction, and disease resistance (Plumb, 1984, Tucker and Robinson, 1990). The comparatively high growth rates of the approximately pH 7 fish in experiments 2 and 3, (SGR, 2.47 and 1.80) indicate that a moderate reduction in the water pH to neutral has a negligible effect on growth. This finding is consistent with previous findings for brown trout (Sulmo truttu) (Jacobsen, 1977). The expected survival rate of hatchery-raised white sturgeon of this age class is approximately 70% (Steffens et al., 1990) and in the present study, the survival rate was 78%. Some mortalities during this study were attributed to the fish ingesting air when swimming over the rising bubbles emanating from the diffuser. Post-mortem, X-ray analysis of these fish (“floaters”) revealed that they developed gastrointestinal emboli which made them positively buoyant. Consequently, they were unable to eat and eventually died of starvation.

Acknowledgements We are grateful for assistance from the following individuals: Paul Lutes and Bill Bentley (UC Davis Aquaculture and Fisheries Program), Megan Sheely, Melissa Gonzalez and Joe Heublein. We are grateful to Drs. A.P. Farrell (Simon Fraser University, B.C., Canada), C. Swanson, P. Young (UC Davis), and two anonymous reviewers for critical review of the manuscript. C.E.C. was partially supported by the UC Davis Patricia Roberts Harris Fellowship and J.J.C. was partially supported by the UC Agricultural Experiment Station (grant no. 3455-H).

References Boutilier, R.G., Heming, T.A. and Iwama, G.K., 1984. Appendix: Physiochemical parameters for use in fish respiratory physiology. In: W.S. Hoar and D.J. Randall (Eds.), Fish Physiology, Vol. 10, Academic Press, New York, p. 416. Cech, J.J., Jr., Mitchell, S.J. and Wragg, T.E., 1984. Comparative growth of juvenile white sturgeon and striped bass: effects of temperature and hypoxia. Estuaries, 7(l): 12- 18. Claibome, J.B. and Heisler, N., 1986. Acid-base regulation and ion transfers in the carp (Cyprinus curpio): pH compensation during graded long- and short-term environmental hypercapnia, and the effect of bicarbonate infusion. 3. Exp. Biol., 126: 41-61. Eddy, F.B., Lomholt, J.P., Weber, R.E. and Johansen, K., 1977. Blood respiratory properties of rainbow trout (S&no gairdneri) kept in water of high CO, tension. J. Exp. Biol., 67: 37-47. Eddy, F.B., Smart, G.R. and Bath, R.N., 1979. Ionic content of muscle and urine in rainbow trout S&no gairdneri Richardson kept in water of high CO, content. J. Fish Dis., 2: 105 110. Green, E.J. and Carritt, D.E., 1967. New tables for oxygen saturation of sea water. J. Mar. Res., 25: 140-147. Heisler, N., 1986. Acid-Base regulation in fishes. In: N. Heisler (Ed.), Acid-Base Regulation in Animals. Elsevier, Amsterdam., pp. 309-356.

C.E. Cracker,

J.J. Cech, Jr./Aquaculrurr

147 (1996)

293-299

299

Hung, S.S.O., Lutes, P.B., Conte, F.S., and Storebakken, T., 1989. Growth and feed efficiency of white sturgeon ( Acipenserlransmontanus) sub-yearlings at different feeding rates. Aquaculture, 80: 147- 1.53. Hung, S.S.O., Lutes, P.B., Shqueir, A.A. and Conte, F.S., 1993. Effect of feeding rate and water temperature on growth of juvenile white sturgeon ( Acipenserfrmsmonrmus). Aquaculture, 115: 297-303. Jacobsen, O.D., 1977. Brown trout (Sukno frufiu L.) growth at reduced pH. Aquaculmre. 11: 81-84. Packer, R.K., 1979. Acid-base and gas exchange in brook trout (Saluelinus ~~h,nrinoli.s) exposed to acid environments. J. Exp. Biol., 79: 127-134. Plumb, J.A., 1984. Relationship of water quality and infectious diseases in cultured channel catfish. Symp. Biol. Hung., 23: 189- 199. Randall, D. and Brauner, C., 1991. Effects of environmental factors on exercise in fish. J. Exp. Biol., 160: 113-126. Ricker, W.E., 1979. Growth rates and models. In: W.S. Hoar, D.J. Randall and J.R. Brett (Eds.), Fish Physiology. Academic Press, New York, Vol. 8, pp. 677-743. Smart, G.R.. Knox, D., Harrison, J.G., Ralph, J.A., Richards, R.H. and Cowey, C.B., 1979. Nephrocalcinosis in rainbow trout Sulmo gairdneri Richardson; the effect of exposure to elevated CO, concentrations. J. Fish Dis., 2: 279-289. Steffens, W., Jahnichen, H. and Fredrich, F., 1990. Possibilities of sturgeon culture in Central Europe. Aquaculture, 89: 101-122. Toews, D.P., Holeton, G.F. and Heisler, N., 1983. Regulation of acid-base status during environmental hypercapnia in the marine teleost fish Conger conger. J. Exp. Biol., 107: 9-20. Tucker, C.S. and Robinson, E.H., 1990. Channel Catfish Farming Handbook. Van Nostrand Reinhold, New York, p. 50. Uhsch, G.R., Ott, M.E. and Heisler, N., 1981. Acid-base and electrolyte status in carp (Cyprinus curpio) exposed to low environmental pH. J. Exp. Biol., 93: 65-80.