Table 1.
Water quality in groups from all trials.
Fig 1.
Measurements of total dissolved gas supersaturation.
Daily mean total dissolved gas (TDG) supersaturation measured in fish tanks in treatment groups T100 (100% TDG, control), T105 (105% TDG), T110 (110% TDG), T115 (115% TDG), and T120 (120% TDG). There were four trials (1-4) including Atlantic salmon (Salmo salar), brown trout (Salmo trutta), and European minnow (Phoxinus phoxinus). Groups T115 in trial 1, T120 in trial 3, and T110 in trial 1 were terminated after 48 hours, 24 hours, and 10 days, respectively, due to high fish mortality or severe clinical signs of gas bubble disease.
Table 2.
Biotic details from the experimental trials 1-4.
Table 3.
Fish size and Fulton’s K for salmonid parr at the onset of trials 1 and 3.
Fig 2.
Clinical signs of gas bubble disease in Atlantic salmon (Salmo salar) parr, manifested as gas embolism in the gills.
Fig 3.
Clinical signs of gas bubble disease in Atlantic salmon (Salmo salar) parr, manifested as internal bleeding in the abdominal cavity. A: Normal, no signs; B: Internal bleeding visible as haemorrhagic ascites.
Fig 4.
Ranked severity of gas bubble formation in fins of salmon parr exposed to different levels of TDG supersaturation.
The mean intensity of subcutaneous emphysema (gas bubbles) in fins of Atlantic salmon (Salmo salar) parr scored on a scale that indicate the coverage of bubbles on the fins: 0 = No bubbles oserved, 1 = less than 25% covered, 2 = 26-50%, and 3 = more than 50%. The groups (T) were exposed to total dissolved gas (%) according to the number in their names. T120 (n = 15) was exposed for 3 hours, T115 (n = 30) was exposed for 24 hours, T110 (n = 15) was exposed for 10 days, T105 (n = 15) was exposed for 13 days, and T100 (control, n = 15) was exposed for 13 days.
Fig 5.
Lethal TDG supersaturation levels for salmon parr during acute gas bubble disease.
Cumulative mortality of Atlantic salmon (Salmo salar) parr exposed to 115% (dotted line; n = 30) and 120% (solid line; n = 30) total dissolved gas (TDG) supersaturation.
Fig 6.
Rates of gas bubble formation in fins to salmon parr during subacute gas bubble disease.
Cumulative prevalence of bubble formation in unpaired (○; caudal and anal) and paired (●; pectoral and pelvic) fins in Atlantic salmon (Salmo salar) parr exposed to total dissolved gas (TDG) of 100% (T100, control), TDG supersaturation of 105% (T105), and TDG supersaturation of 110% (T110). The formation of bubbles is expressed as a linear regression, where the coefficient of determination (R2) was > 0.95 for all exposure groups, except for the paired fins of fish in treatment group T100 (R2 = 0.74).
Fig 7.
Progress in formation of gas bubbles in fins of salmon parr during subacute gas bubble disease.
Mean fin score of severity was measured in fish exposed to 110% total dissolved gas (TDG) supersaturation during a period of 10 days (T110). Observations of gas bubble formations in unpaired fins (○ and dotted line; caudal and anal fins) and paired fins (● and solid line; pectoral and pelvic fins) of Atlantic salmon (Salmo salar) parr. N = 5 to 15 fish per dot. Severity of bubble formation ranked on a scale that indicate the coverage of bubbles on the fins: 0 = No bubbles observed, 1 = less than 25% covered, 2 = 26-50%, and 3 = more than 50%. Rates of severity are expressed as a linear regression (y = 0.1037x + 0.1931 for unpaired and y = 0.0485x + 0.4698 for paired). The respective coefficients of determination (R2) and p-values are shown in the figure.
Table 4.
Clinical signs of gas bubble disease (GBD) in Atlantic salmon parr (Salmo salar) from trial 1.
Fig 8.
Common signs of acute and subacute gas bubble disease in Atlantic salmon (Salmo salar) parr.
Gas bubble formations in (A) Caudal fins; (B) Anal fin; (C) Pectoral fin; (D) Pelvic fin.
Fig 9.
Observed signs of subacute gas bubble disease in Atlantic salmon (Salmo salar) parr.
(A) Gas bubble on operculum; (B) Gas bubbles in buccal cavity; (C) Bilateral exophthalmia.
Fig 10.
Clinical signs of gas bubble disease in alevin.
Appearance of gas bubbles in the intestine to Atlantic salmon (Salmo salar) alevin exposed to 120% total dissolved gas supersaturation for 12 days. Photo (B) is an enlarged part of photo (A).
Fig 11.
Blue sac disease in Atlantic salmon (Salmo salar) alevin.
Ascites fluid in yolk sac to alevins that have been exposed to (A) 110% and (B) 115% total dissolved gas supersaturation for two weeks.
Fig 12.
Lethal TDG supersaturation levels for salmon fry.
Cumulative mortality of Atlantic salmon (Salmo salar) fry exposed to 120% total dissolved gas (TDG) supersaturation (n = 43).
Fig 13.
Clinical signs of subacute gas bubble disease in Atlantic salmon (Salmo salar) fry.
Gas bubble formation (subcutaneous emphysema) in the lower jaw (A, B), in lower jaw, operculum, and behind the eye (C), in jaws, buccal cavity, and operculum (D).
Fig 14.
Cumulative frequencies of observed subcutaneous emphysema in Atlantic salmon (Salmo salar) fry.
Occurrence of gas bubbles in operculum, buccal cavity, and head region of fry exposed to 110% (n = 30), 115% (n = 30) and 120% (n = 30) total dissolved gas. Gas bubbles on the head region were only observed in fry exposed to 120% total dissolved gas (TDG) supersaturation.
Fig 15.
Observations of as bubbles in the gastrointestinal (GI) tract of salmon fry.
Observed gas bubbles in the GI tract of Atlantic salmon (Salmo salar) fry exposed to total dissolved gas (TDG) supersaturation. (A) Gas in the intestine after exposure of 120% TDG for 5 days; (B) Gas bubbles in stomach and intestine after exposure of 110% TDG for 12 days; (C) Gas in the stomach after exposure of 120% TDG for 12 days; (D) Gas bubbles in the intestine after exposure of 115% TDG for 5 days.
Fig 16.
Rates of gas bubble formations in the gastrointestinal (GI) tract of salmon fry.
Cumulative frequency (%) of observed gas bubbles in the GI tract of Atlantic salmon (Salmo salar) fry exposed to total dissolved gas supersaturation of 110% (T110; ○), 115% (T115; ▲), and 120% (T120; ●). Each dot represents 10 fish. The frequency expressed as a linear regression (fitted line) for T110 (y = 0.0086x − 0.0055), T115 (y = 0.0329x + 0.0683), and T120 (y = 0.061x + 0.0352). The respective coefficients of determination (R2) and p-values are shown in the figure.
Table 5.
Clinical signs of gas bubble disease (GBD) in Atlantic salmon fry (Salmo salar) from trial 2b.
Fig 17.
Cataract in brown trout (Salmo trutta) parr exposed to 115% total dissolved gas supersaturation for 48 hours. (A) Cataract covering 6% of the lens, (B) 12% of the lens; (C) 23% of the lens.
Fig 18.
Gas bubble formation in the lateral line of brown trout (Salmo trutta) parr exposed to total dissolved gas supersaturation of 120% (A, B) and 100% (C). (A) Total occlusion of the lateral line by gas bubbles; (B) Scattered bubble formation; (C) Scattered bubble formation.
Table 6.
Clinical signs of gas bubble disease (GBD) in bown trout parr (Salmo trutta) from trial 3.
Fig 19.
Ranked severity of gas bubble formation in fins and lateral line of brown trout exposed to different levels of TDG supersaturation.
The mean intensity of gas bubbles scored on a scale that indicate the coverage of bubbles on the fins or lateral line of brown trout (Salmo trutta) parr: 0 = No bubbles observed, 1 = less than 25% covered with bubbles, 2 = 26-50%, and 3 = more than 50%. The treatment groups (T) were exposed to total dissolved gas (TDG) supersaturation (%) according to the number in their name. T120 (n = 22) was exposed for 13 hours, T115 (n = 20) was exposed for 48 hours, and T110 (n = 21) was exposed for 14 days.
Fig 20.
Lethal TDG supersaturation levels for brown trout during acute gas bubble disease.
Cumulative mortality of brown trout (Salmo trutta) parr exposed to 115% (dotted line, n = 50) and 120% (solid line, n = 50) total dissolved gas (TDG) supersaturation.
Fig 21.
Gill embolism and mortality rates observed in brown trout during subacute gas bubble disease.
Cumulative frequency of observed gill embolism and mortality or moribund brown trout (Salmo trutta) parr in group T110 exposed to 110% total dissolved gas supersaturation (TDG) over 14 days. Cumulative frequency of observations is expressed as a linear regression (fitted line) for gas embolism in gills (○; y = 0.0367x − 0.0867) and for mortality or moribund fish (●; y = 0.0123x − 0.0079). The respective coefficients of determination (R2) and p-values are shown in the figure.
Fig 22.
Rates of gas bubble formation in the fins and lateral lines of brown trout during subacute gas bubble disease.
Progression of bubble formation in brown trout (Salmo trutta) parr exposed to 110% total dissolved gas supersaturation. Cumulative prevalence of bubble formation in unpaired fins (○; caudal and anal), paired fins (●; pectoral and pelvic) and lateral line (△). Formation of bubbles expressed as linear regression for unpaired fins: y = 0.0498x-0.1581; paired fins: y = 0.0362x-0.0719; lateral line: y = 0.0552x-0.1511. R2 (coefficient of determination) > 0.89 for all.
Fig 23.
Clinical signs of gas bubble disease in trout during subacute gas bubble disease in brown trout.
Subacutes signs of gas bubble disease in brown trout (Salmo trutta) parr exposed to 110% total dissolved gas supersaturation. (A) Bubble formation on the gill arches; (B) Gas bubbles in the nostrils; (C) gas bubble formation in the choroid gland in the eye of a specimen exhibiting exophthalmia; (D) Hemorrhages in the head region.
Fig 24.
Recovery from gas bubble disease in brown trout (Salmo trutta) parr.
(A) Subcutaneous emphysema (gas bubbles) in the caudal fin after exposure to 110% total dissolved gas supersaturation (TDGS) for 13 days; (B) Scars in caudal fin after seven days of recovery in 100% TDG; (C) Gas bubbles in the choroid gland in the eye after 110% TDGS for 13 days; (D) Choroid gland after seven days of recovery in 100% total dissolved gas.
Fig 25.
Lethal TDG supersaturation levels for salmon and rainbow trout parr during acute gas bubble disease in Trial 3.
Cumulative mortality in parr of Atlantic salmon (Salmo salar, solid line; n = 16) and rainbow trout (Oncorhynchus mykiss, dotted line; n = 16) exposed to 120% total dissolved gas supersaturation.
Table 7.
Clinical signs of gas bubble disease (GBD) in Atlantic salmon parr (Salmo salar) and rainbow trout (Oncorhynchus mykiss) from trial 3.
Fig 26.
Clinical signs of gas bubble disease in adult European minnow (Phoxinus phoxinus) exposed to 120% total dissolved gas supersaturation.
A: Subcutaneous emphysema (gas bubble) at the basis of the pectoral fin; B: Gas bubble formation in the gill chamber and basis of the pectoral fin; C: Gas bubble formation on the neck; D: Gas bubble formation on the head region, including operculum, nostrils, and eye.
Fig 27.
Lethal TDG supersaturation levels for adult minnow.
Cumulative mortality of adult European minnow (Phoxinus phoxinus). The treatment groups (T) were exposed to total dissolved gas (TDG) supersaturation (%) according to the number in their name.
Table 8.
Clinical signs of gas bubble disease (GBD) in adult European minnow (Phoxinus phoxinus) from trial 4.
Table 9.
Inter- and intraspecific difference in tolerance of salmonids to total dissolved gas supersaturation.