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An explanation for the high resistance of incubating salmonid eggs to atmospheric gas supersaturation of water
Aquaculture, 49 (1985) 85-88 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
85
Short Communication AN EXPLANATION FOR THE HIGH RESISTANCE OF INCUBATING SALMONID EGGS TO ATMOSPHERIC GAS SUPERSATURATION OF WATER
D.F. ALDERDICE
and J.O.T.
JENSEN
Department of Fisheries and Oceans, Fisheries Research Branch, Pacific Biological Station, Nanaimo, B.C. V9R 5K6 (Canada) (Accepted
27 June 1985)
ABSTRACT Alderdice, D.F. and Jensen, J.O.T., 1985. An explanation for the high resistance of incubating salmonid eggs to atmospheric gas supersaturation of water. Aquaculture, 49: 85-88. Embryonic stages of development within the salmonid egg are more resistant to the effects of atmospheric gas supersaturation, compared with later stages following hatching. We show that the hydrostatic pressure maintained under the capsule (zona radiata) of the egg is sufficient to compensate for a substantial portion of the excess total gas pressure to which the egg may be exposed in supersaturated water. That is, total gas pressure thresholds for gas bubble trauma are raised above those applying to later developmental stages, following hatching, as a result of normal infracapsular pressure.
INTRODUCTION
It has long been known that atmospheric gas supersaturation of water can cause adverse effects in exposed aquatic organisms (Weitkamp and Katz, 1980). The problem has been called gas bubble disease; we prefer the name gas bubble trauma (GBT) as pathogens are not primarily involved. Generally, problems of supersaturation are considered relative to nitrogen, oxygen and argon gases, which constitute about 99.964% of a given volume of atmospheric air. Colt (1980, 1983) shows that the total pressure of gases (TGP) dissolved in water (liquid phase, I) is in equilibrium with those gases in the atmosphere (gas phase, g) when TGI’=(i
Z’;)+Pn,O=BP=( i=i
where
i
pf:)+P,,,
i=i
BP = barometric pressure (mm Hg) at the water surface P = pressure of the component gases (mm Hg) PH,O = pressure of water vapour (mm Hg)
0044-8486/85/$03.30
o 1985 Elsevier Science Publishers B.V.
(1)
86
At equilibrium, TGP = BP. Water is supersaturated when TGP > BP; it is undersaturated when TGP < BP. Recently developed membrane diffusion instruments are used to measure AP, the difference between TGP and BP (mm Hg) when TGP > BP. AP is now recognized as the driving force responsible for bubble growth in GBT. Although TGP = AP + BP is the most meaningful expression for gas supersaturation, the tradition of reporting dissolved gas levels in terms of percentage saturation continues. Hence TGP (% satn.) = ( BpB;Ap)
X 100
(2)
Alderdice et al. (1984) measured the hydrostatic or internal pressure beneath the capsule of salmonid eggs (Oncorhynchus spp. and Salmogairdneri). They found the internal pressure to be at least 15 mm Hg 2 h after activation and at least 25 mm Hg after 24 h. Internal pressures near hatching ranged between 50 and 90 mm Hg, depending on the species. Let us assume that eggs with an internal pressure of 50 mm Hg are being held in water, just below the surface (depth = 0 m), and that the water is in equilibrium at atmospheric gas saturation (BP = 760 mm Hg, APwater = 0). However, the egg with its higher internal pressure would be in equilibrium with a TGP greater than saturation. Therefore, replacing AP,,,,, = 0 with AP,% = 50 in equation 2 provides an estimate of the TGP (% saturation) at which the egg would be in equilibrium: ( 76;6;50
)
x 100 = 106.6%
Under similar conditions an egg with an internal pressure of 90 mm Hg would be in equilibrium with a TGP of 111.8% saturation. Therefore internal pressures of 50 to 90 mm Hg will provide the equivalent of 100% saturation for eggs held just below the surface when the TGP of the perfusing water is 106.6 to 111.8% of saturation, respectively. There is growing evidence, based largely on analysis of available data, that salmonids in fresh water, during later stages of development after hatching, respond to excess TGP as follows (Fidler, 1984; Wright and McLean, 1984; Jensen et al., 1985; Alderdice and Jensen, 1985; Jensen et al., unpubl.). Recent studies suggest that GBT should be divided into two types - chronic and acute. Chronic GBT in salmonids appears to begin at a TGP level of 104-105% saturation, the range extending to about 109~-110% TGP. Mortality is associated with extravascular bubble growth and is low (1.55.0%) over an extended period of exposure. At and above about 110% TGP, intravascular bubble formation occurs; mortality is rapid and extensive over much shorter periods of exposure. In addition there is no single level of TGP separating the two types of GBT. The incipient lethal level of TGP for acute GBT (about 108-116% TGP) is determined by the combination of levels of other variables at which exposure occurs. We find the most impor-
87
tant of these other variables to be water depth, the ratio of dissolved oxygen/ dissolved nitrogen in the water, and fish size. In general, a nominal level of 110% TGP may be taken as a reasonable boundary (e.g. at 0.1 m water depth, 0.95-1.0 Oz/Nz ratio, 65 mm total length) within the transitional range. After hatching, later stages are assumed to respond to TGP in terms of tissue sensitivity, without the protection provided by the hydrostatic pressure contained by the egg capsule. From the recent studies previously mentioned we believe that the TGP (% saturation) levels associated with tissue sensitivity thresholds in salmonids are near 104 and 110% for chronic and acute GBT, respectively. The base levels of tissue sensitivity in the egg stage then would be raised by 6.6 to 11.8% excess TGP as a result of the hydrostatic pressure under the egg capsule. On that basis the chronic and acute thresholds for GBT, in eggs with internal pressures of 50 and 90 mm Hg, should be approximately those shown in Table 1. Under the conditions indicated we suggest that salmonid eggs with internal pressures of 50-90 mm Hg would be subject to chronic GBT in the range of about ill-116% TGP, and to acute GBT in the range of 117-122’S TGP and higher. It appears that the internal pressures found in salmonid eggs should protect them from the generally low levels of supersaturation that may occur in hatchery (shallow water incubation) situations. Although embryos may be protected from TGP problems through the action of infracapsular hydrostatic pressure, it is obvious that the compensatory mechanism is lost at hatching. At that time the aforementioned estimates of TGP (%) thresholds associated with chronic (104-105% TGP) and acute (log--110%) GBT would apply. TABLE 1 Estimated chronic and acute thresholds for GBT Nominal TGP at surface
Hydrostatic pressure (HP) of eggs (mm Hg) at 0 m depth 50
(% satn.)
Portion of nom. TGP compensated by HP (% satn.)
Estimated threshold TGP (% satn.)
Portion of nom. TGP compensated by HP (% satn.)
Estimated threshold TGP (% satn.)
104 110
6.6 6.6
110.6 116.6
11.8 11.8
115.8 121.8
90
REFERENCES Alderdice, D.F. and Jensen, J.O.T., 1985. Assessment of the influence of gas supersaturation on salmonids in the Nechako River in relation to Kemano Completion. Can. Tech. Rep. Fish. Aquat. Sci., No. 1386, 48 pp.
88 Alderdice, D.F., Jensen, J.O.T. and Velsen, F.P.J., 1984. Measurement of hydrostatic pressure in salmonid eggs. Can. J. Zool., 62: 1977-1987. Colt, J.E., 1980. The computation of dissolved gas levels in water as a function of temperature, salinity and pressure. Dept. Civil Engineering, Univ. California, Davis, CA, 81 pp. Colt, J.E., 1983. The computation and reporting of dissolved gas levels. Water Res., 17: 841-849. Fidler, L.E., 1984. A study of biophysical phenomena associated with gas bubble trauma in fishes. Penny Applied Sciences Ltd., Penny, B.C., 132 pp. (unpubl.). Jensen, J.O.T., Hally, A.M. and Schnute, J., 1986. Literature data on salmonid response to gas supersaturation and ancillary factors. Can. Data Rep. Fish. Aquat. Sci., No. 501, 35 PP. Jensen, J.O.T., Schnute, J. and Alderdice, D.F., unpubl. Assessing sahnonid response to gas supersaturation with a new multivariable dose-response model. MS, Pacific Bioldgical Station, Nanaimo, B.C. Weitkamp, D.E. and Katz, M., 1980. A review of dissolved gas supersaturation literature. Trans. Am. Fish. Sot., 109: 659-702. Wright, P.B. and McLean, W.E., 1984. The effects of aeration on the rearing of summer chinook fry (Oncorhynchus tshawytscha) at the Puntledge Hatchery. Dept. Fish. Oceans, Vancouver, B.C., 47 pp. (unpubl.).
85
Short Communication AN EXPLANATION FOR THE HIGH RESISTANCE OF INCUBATING SALMONID EGGS TO ATMOSPHERIC GAS SUPERSATURATION OF WATER
D.F. ALDERDICE
and J.O.T.
JENSEN
Department of Fisheries and Oceans, Fisheries Research Branch, Pacific Biological Station, Nanaimo, B.C. V9R 5K6 (Canada) (Accepted
27 June 1985)
ABSTRACT Alderdice, D.F. and Jensen, J.O.T., 1985. An explanation for the high resistance of incubating salmonid eggs to atmospheric gas supersaturation of water. Aquaculture, 49: 85-88. Embryonic stages of development within the salmonid egg are more resistant to the effects of atmospheric gas supersaturation, compared with later stages following hatching. We show that the hydrostatic pressure maintained under the capsule (zona radiata) of the egg is sufficient to compensate for a substantial portion of the excess total gas pressure to which the egg may be exposed in supersaturated water. That is, total gas pressure thresholds for gas bubble trauma are raised above those applying to later developmental stages, following hatching, as a result of normal infracapsular pressure.
INTRODUCTION
It has long been known that atmospheric gas supersaturation of water can cause adverse effects in exposed aquatic organisms (Weitkamp and Katz, 1980). The problem has been called gas bubble disease; we prefer the name gas bubble trauma (GBT) as pathogens are not primarily involved. Generally, problems of supersaturation are considered relative to nitrogen, oxygen and argon gases, which constitute about 99.964% of a given volume of atmospheric air. Colt (1980, 1983) shows that the total pressure of gases (TGP) dissolved in water (liquid phase, I) is in equilibrium with those gases in the atmosphere (gas phase, g) when TGI’=(i
Z’;)+Pn,O=BP=( i=i
where
i
pf:)+P,,,
i=i
BP = barometric pressure (mm Hg) at the water surface P = pressure of the component gases (mm Hg) PH,O = pressure of water vapour (mm Hg)
0044-8486/85/$03.30
o 1985 Elsevier Science Publishers B.V.
(1)
86
At equilibrium, TGP = BP. Water is supersaturated when TGP > BP; it is undersaturated when TGP < BP. Recently developed membrane diffusion instruments are used to measure AP, the difference between TGP and BP (mm Hg) when TGP > BP. AP is now recognized as the driving force responsible for bubble growth in GBT. Although TGP = AP + BP is the most meaningful expression for gas supersaturation, the tradition of reporting dissolved gas levels in terms of percentage saturation continues. Hence TGP (% satn.) = ( BpB;Ap)
X 100
(2)
Alderdice et al. (1984) measured the hydrostatic or internal pressure beneath the capsule of salmonid eggs (Oncorhynchus spp. and Salmogairdneri). They found the internal pressure to be at least 15 mm Hg 2 h after activation and at least 25 mm Hg after 24 h. Internal pressures near hatching ranged between 50 and 90 mm Hg, depending on the species. Let us assume that eggs with an internal pressure of 50 mm Hg are being held in water, just below the surface (depth = 0 m), and that the water is in equilibrium at atmospheric gas saturation (BP = 760 mm Hg, APwater = 0). However, the egg with its higher internal pressure would be in equilibrium with a TGP greater than saturation. Therefore, replacing AP,,,,, = 0 with AP,% = 50 in equation 2 provides an estimate of the TGP (% saturation) at which the egg would be in equilibrium: ( 76;6;50
)
x 100 = 106.6%
Under similar conditions an egg with an internal pressure of 90 mm Hg would be in equilibrium with a TGP of 111.8% saturation. Therefore internal pressures of 50 to 90 mm Hg will provide the equivalent of 100% saturation for eggs held just below the surface when the TGP of the perfusing water is 106.6 to 111.8% of saturation, respectively. There is growing evidence, based largely on analysis of available data, that salmonids in fresh water, during later stages of development after hatching, respond to excess TGP as follows (Fidler, 1984; Wright and McLean, 1984; Jensen et al., 1985; Alderdice and Jensen, 1985; Jensen et al., unpubl.). Recent studies suggest that GBT should be divided into two types - chronic and acute. Chronic GBT in salmonids appears to begin at a TGP level of 104-105% saturation, the range extending to about 109~-110% TGP. Mortality is associated with extravascular bubble growth and is low (1.55.0%) over an extended period of exposure. At and above about 110% TGP, intravascular bubble formation occurs; mortality is rapid and extensive over much shorter periods of exposure. In addition there is no single level of TGP separating the two types of GBT. The incipient lethal level of TGP for acute GBT (about 108-116% TGP) is determined by the combination of levels of other variables at which exposure occurs. We find the most impor-
87
tant of these other variables to be water depth, the ratio of dissolved oxygen/ dissolved nitrogen in the water, and fish size. In general, a nominal level of 110% TGP may be taken as a reasonable boundary (e.g. at 0.1 m water depth, 0.95-1.0 Oz/Nz ratio, 65 mm total length) within the transitional range. After hatching, later stages are assumed to respond to TGP in terms of tissue sensitivity, without the protection provided by the hydrostatic pressure contained by the egg capsule. From the recent studies previously mentioned we believe that the TGP (% saturation) levels associated with tissue sensitivity thresholds in salmonids are near 104 and 110% for chronic and acute GBT, respectively. The base levels of tissue sensitivity in the egg stage then would be raised by 6.6 to 11.8% excess TGP as a result of the hydrostatic pressure under the egg capsule. On that basis the chronic and acute thresholds for GBT, in eggs with internal pressures of 50 and 90 mm Hg, should be approximately those shown in Table 1. Under the conditions indicated we suggest that salmonid eggs with internal pressures of 50-90 mm Hg would be subject to chronic GBT in the range of about ill-116% TGP, and to acute GBT in the range of 117-122’S TGP and higher. It appears that the internal pressures found in salmonid eggs should protect them from the generally low levels of supersaturation that may occur in hatchery (shallow water incubation) situations. Although embryos may be protected from TGP problems through the action of infracapsular hydrostatic pressure, it is obvious that the compensatory mechanism is lost at hatching. At that time the aforementioned estimates of TGP (%) thresholds associated with chronic (104-105% TGP) and acute (log--110%) GBT would apply. TABLE 1 Estimated chronic and acute thresholds for GBT Nominal TGP at surface
Hydrostatic pressure (HP) of eggs (mm Hg) at 0 m depth 50
(% satn.)
Portion of nom. TGP compensated by HP (% satn.)
Estimated threshold TGP (% satn.)
Portion of nom. TGP compensated by HP (% satn.)
Estimated threshold TGP (% satn.)
104 110
6.6 6.6
110.6 116.6
11.8 11.8
115.8 121.8
90
REFERENCES Alderdice, D.F. and Jensen, J.O.T., 1985. Assessment of the influence of gas supersaturation on salmonids in the Nechako River in relation to Kemano Completion. Can. Tech. Rep. Fish. Aquat. Sci., No. 1386, 48 pp.
88 Alderdice, D.F., Jensen, J.O.T. and Velsen, F.P.J., 1984. Measurement of hydrostatic pressure in salmonid eggs. Can. J. Zool., 62: 1977-1987. Colt, J.E., 1980. The computation of dissolved gas levels in water as a function of temperature, salinity and pressure. Dept. Civil Engineering, Univ. California, Davis, CA, 81 pp. Colt, J.E., 1983. The computation and reporting of dissolved gas levels. Water Res., 17: 841-849. Fidler, L.E., 1984. A study of biophysical phenomena associated with gas bubble trauma in fishes. Penny Applied Sciences Ltd., Penny, B.C., 132 pp. (unpubl.). Jensen, J.O.T., Hally, A.M. and Schnute, J., 1986. Literature data on salmonid response to gas supersaturation and ancillary factors. Can. Data Rep. Fish. Aquat. Sci., No. 501, 35 PP. Jensen, J.O.T., Schnute, J. and Alderdice, D.F., unpubl. Assessing sahnonid response to gas supersaturation with a new multivariable dose-response model. MS, Pacific Bioldgical Station, Nanaimo, B.C. Weitkamp, D.E. and Katz, M., 1980. A review of dissolved gas supersaturation literature. Trans. Am. Fish. Sot., 109: 659-702. Wright, P.B. and McLean, W.E., 1984. The effects of aeration on the rearing of summer chinook fry (Oncorhynchus tshawytscha) at the Puntledge Hatchery. Dept. Fish. Oceans, Vancouver, B.C., 47 pp. (unpubl.).