Effects of environmental pH and calcium on ammonia toxicity in channel catfish

Journal article

The 24-hour median lethal concentrations (24-hour LC50) of total ammonia nitrogen (TA-N) to channel catfish (Ictalarus punctatus) at pH 7, 8, and 9 (total hardness, 40 mg/l; temperature, 21-25 C) were 263.6 ± 11.3 (SE), 38.8 ± 1.8, and 4.5 ± 0.2 mg/l, respectively. The 24-hour LC50 of un-ionized ammonia nitrogen (UIA-N) concentration at pH 8 was significantly higher (1.82 ± 0.06 mg/l) than at pH 7 or 9 (1.39 ± 0.06 and 1.49 ± 0.12 mg/l). Enrichment of the water to 440 mg/l total hardness at pH 7 significantly increased the 24-hour LC50 of TA-N and UIA-N (356.3 ± 16.4 and 1.79 ± 0.07). Fish exposed to 25 mg/l TA-N for 12 hours at pH 7 and 8 showed no differences from control fish in hematocrit percent total plasma protein, or plasma and muscle chloride. Plasma sodium showed no difference between control and experimental groups at pH 7: however, a significant decrease occurred in fish exposed to 25 mg/l TA-N at pH 8. No differences in blood pH were found between the control groups and fish exposed to 100 and 200 mg/l TA-N at pH 7, and to 10 and 25 mg/l TA-N at pH 8. Plasma sodium depletion is suggested as a contributing mechanism of ammonia toxicity.

Authors: Tomasso, JR; Goudie, C; Simco, B; Davis, K

• Journal: Transactions of the American Fisheries Society
• Volume: 109
• Issue: 2
• Pages: 229-234
• Publication date: 1980-01-01
• ISSN: 0002-8487
• Language: English