Cardiac and opercular responses in channel catfish (Ictalurus punctatus) exposed to high levels of phosphate

Abstract

Channel catfish were exposed to elevated levels of phosphate in three different experimental regimes with cardiac and opercular rates being monitored by the use of unimplanted electrodes. Fish exposed to 20 mg/l phosphate, in 2 mg/l increasing increments, had peak mean cardio‐opercular rates at 12 mg/l. The elevated cardiac rates were significant at both the 10 and 12 mg/l concentrations. Fish exposed to 160 mg/l phosphate, in 20 mg/l increasing increments, had peak mean cardio‐opercular rates at 20 mg/l. The fish exposed to 20 mg/l phosphate in 5 mg/l increments, maintained at 20 mg/l for a two week period and then returned to zero in 5 mg/l increments had cardio‐opercular rates similar to those of the two acute studies. During the 2 week continuous exposure to the 20 mg/l phosphate the mean cardiac rate increased 8% and the opercular rate decreased 13%. At the termination of this experiment both the cardiac and opercular rates returned to their pre‐experiment levels.

Previous work by Cairns and co‐workers^1–5, Sparks et al.⁶, Sellers et al.⁷ and Westlake and van der Schalie⁸ has suggested approaches for measuring the effects of toxicants by recording movements or breathing rates or both. W.S.G. Morgan^9–12 has demonstrated a biological automonitor for continuous water quality control which is sensitive to between 5 and 10% of the 48‐hour LC⁵⁰ of the fish sensor. Likewise, Bahr¹³ has studied the cardiac and lateral line responses in trout exposed to toxicants, and O'Hara¹⁴ has studied alterations in oxygen consumption in bluegills exposed to copper. Drummond^15–16 has evaluated the cough response in fish exposed to mercuric compounds, and E.C. Morgan¹⁷ and Bonner and Morgan¹⁸ have studied the swimming activity and breathing rates in an automated system in which hydrofluoric acid and phossy water were present. Cardiac rhythms have been widely employed by physiologists and behaviorists as a first step in determining when an organism is in a stressful situation. Rommel¹⁹ and Strange et al. ²⁰ have described methods for recording cardiac and cardiac‐opercular rates in marine and freshwater environments. This researcher has developed and used an unimplanted electrode system to monitor cardiac, opercular, and cough rate responses in channel catfish (Ictalurus punctatus) exposed to varying water quality situations^20–23.

In eutrophic lakes such as the Flat Creek Embayment of Lake Sidney Lanier northeast of Atlanta, Georgia near Gainesville, aquatic crganisms have had to adapt to a changing environment. This change has resulted from the introduction of substances at levels higher than they occurred naturally. One such substance is phosphate. Phosphate levels are more often altered by man's activities than any of the other substances in water pollution. Input of phosphorus into a system can originate from industrial and sewage effluents, less controllable non‐point sources would still be a problem. Stumm²⁴ has estimated that the removal of 90% of the phosphates in waste water would result in a reduction of only 40 to 80% of the total found in a lake.

Experimental evidence has indicated that luxury levels of phosphorus affect the functioning of an ecosystem at the level of primary production²⁰,²². With the utilization of phosphorus by primary producers already examined in some detail, it was the purpose of this experiment to determine if elevated levels of phosphates would alter the cardiac and opercular activities of the channel catfish, a natural inhibitant of the Flat Creek Embayment of Lake Sidney Lanier.

Key words:

• Cardiac rate
• opercular rate
• channel catfish (Ictalurus punctatus)
• phosphate.