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First published online May 13, 2004
Journal of Experimental Biology 207, 2043-2054 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00990

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Dogmas and controversies in the handling of nitrogenous wastes: Is exogenous ammonia a growth stimulant in fish?

Chris M. Wood^*

Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1

View larger version (18K): [in a new window]   Fig. 1. (A) Body mass of individually marked fish over 70 days in the three experimental treatments of Series 1: nominal, [TAmm]=0 µmol l–1 (control, N=13), [TAmm]=70 µmol l–1 (low ammonia, N=7) and [TAmm]=225 µmol l–1 (high ammonia, N=16). Values are means ±1 S.E.M. There were no significant differences at any time, but ANCOVA indicated higher overall growth (P<0.055, two-tail; P<0.028, one-tail) in the low ammonia treatment relative to the control. (B) Cumulative food consumption per fish, measured on a tank basis (N=4 for control and high ammonia, N=2 for low ammonia) in this same series. By Day 70, cumulative food consumption in the high ammonia treatment group was significantly greater (asterisk) than in the other two treatment groups.

View larger version (11K): [in a new window]   Fig. 2. Growth indices of individually marked fish over 70 days in the three experimental treatments of Series 1: nominal [TAmm]=0 µmol l–1 (control, N=13), 70 µmol l–1 (low ammonia, N=7), and 225 µmol l–1 (high ammonia, N=16). (A) Mass gain per fish, (B) specific growth rate (SGR) and (C) condition factor (CF). Values are means ±1 S.E.M. *Significant difference from control.

View larger version (16K): [in a new window]   Fig. 3. (A) Gross food conversion efficiency (CE) measured on a tank basis (N=4 for control and high ammonia, N=2 for low ammonia) and (B) protein production per individual fish (N=12 for control and high ammonia, N=6 for low ammonia) over 70 days in the three experimental treatments of Series 1: nominal [TAmm]=0 µmol l–1 (control), 70 µmol l–1 (low ammonia), and 225 µmol l–1 (high ammonia). Values are means ±1 S.E.M. *Significant difference from control.

View larger version (17K): [in a new window]   Fig. 4. Mean rates of (A) `in-tank' O2 consumption (O2, 5–6 h post-feeding) and (B) `in-tank' ammonia excretion (Amm, 5–8 h post-feeding) measured once per week over 9 weeks in each of the treatment tanks of Series 1 (N=36 for the control and high ammonia treatments, N=22 for the low ammonia treatment). The data were mass-corrected using the mass exponent 0.824 determined for rainbow trout by Cho (1990). Values are means ±1 S.E.M. *Significant difference from control.

View larger version (27K): [in a new window]   Fig. 5. Measured levels of total ammonia on each day in the nominal [TAmm]=0 µmol l–1, (control, N=4), 70 µmol l–1 (low ammonia, N=4) and 225 µmol l–1 (high ammonia, N=3) treatment tanks of Series 2. Values are means ±1 S.E.M.

View larger version (18K): [in a new window]   Fig. 6. Body mass of individually marked fish at weekly intervals over 71 days in the three experimental treatment groups of Series 2: nominal [TAmm]=0 µmol l–1 (control, N=64), 70 µmol l–1 (low ammonia, N=64), and 225 µmol l–1 (high ammonia, N=48). Values are means ±1 S.E.M. (A) Satiation-fed fish, (B) rationed fish. Within A, asterisks indicate mean body mass significantly higher than the corresponding control mean, and crosses indicate mean body mass significantly lower than the corresponding control mean. ANCOVA indicated significantly higher overall growth over 71 days in the high ammonia treatment, and no significant difference in overall growth over 71 days in the low ammonia treatment relative to controls. Within B, there were no significant differences.

View larger version (15K): [in a new window]   Fig. 7. Specific growth rates (SGR) of individually marked fish over 71 days in the three experimental treatment groups of Series 2: nominal [TAmm]=0 µmol l–1 (control, N=64), 70 µmol l–1 (low ammonia, N=64), and 225 µmol l–1 (high ammonia, N=48). (A) Satiation-fed fish, (B) rationed fish. Values are means ±1 S.E.M. *Significant difference from control within the same panel. SGR values for the same treatments were all significantly lower in the rationed fish than in the satiation-fed fish.

View larger version (33K): [in a new window]   Fig. 8. Daily ration, measured on a per tank basis and expressed on a % body mass per day basis [(g food g–1 fish)x100] over 71 days in three experimental treatments of Series 2: nominal [TAmm]=0 µmol l–1 (control, N=4 tanks), 70 µmol l–1 (low ammonia, N=4 tanks) and 225 µmol l–1 (high ammonia, N=3 tanks). Values are means ±1 S.E.M. Data for satiation-fed fish represent voluntary food consumption. Values for the high ammonia treatment group tended to be lower than the controls late in the exposure, but overall there were no statistically significant differences. Data for rationed fish reflect the fact that these fish were fed a fixed ration of 2% of their body mass per day, not all of which was consumed. Again, there were no significant differences overall.

View larger version (14K): [in a new window]   Fig. 9. Gross food conversion efficiency (CE) measured on a tank basis (N=4 for control and low ammonia groups, N=3 for high ammonia group) over 71 days in the three experimental treatments of Series 2: nominal [TAmm]=0 µmol l–1 (control), 70 µmol l–1 (low ammonia) and 225 µmol l–1 (high ammonia). (A) Satiation-fed fish, (B) rationed fish. Values are means ±1 S.E.M. *Significant difference from control within the same panel. CE values for the same treatments were all significantly lower in the rationed fish than in the satiation-fed fish.

View larger version (14K): [in a new window]   Fig. 10. Protein production per individual fish (N=20 for control and low ammonia, N=15 for high ammonia) over 71 days in the three experimental treatments of Series 2: nominal [TAmm]=0 µmol l–1 (control), 70 µmol l–1 (low ammonia) and 225 µmol l–1 (high ammonia). (A) Satiation-fed fish, (B) rationed fish. Values are means ±1 S.E.M. *Significant difference from control within the same panel. Means for the same treatments were all significantly lower in the rationed fish than in the satiation-fed fish.