Effects of formalin on water quality and parasitic monogeneans on silver perch (Bidyanus bidyanus Mitchell) in earthen ponds
2006
Rowland, Stuart J. | Nixon, Mark | Landos, Matthew | Mifsud, Charlie | Read, Phil | Boyd, Peter
Infestations of parasitic monogenean trematodes (Lepidotrema bidyana and Gyrodactylus sp.) on freshwater silver perch (Bidyanus bidyanus Mitchell) in earthen ponds were treated with formalin (37% formaldehyde). Concentrations of 30 and 40 mg L⁻¹ formalin were effective, but fish in ponds treated with 20 or 25 mg L⁻¹ remained infested. At temperatures of 24.1-26.9°C, concentrations of 30 or 40 mg L⁻¹ formalin caused dissolved oxygen (DO) to decline from 10.1-11.9 to 3.0-3.3 and 1.2-1.7 mg L⁻¹, respectively, within 36-42 h of treatment. In addition, pH declined from 7.2-8.4 to 6.3-6.7, within 36 h and turbidity decreased over 48 h. In the ponds where DO was 1.2-1.7 mg L⁻¹, silver perch showed signs of severe stress, but continuous aeration (10 hp ha⁻¹) for 3 days and inflow of well-oxygenated water for 6-8 h prevented mortalities. At temperatures of 13.2-15.7°C, concentrations of 30 or 40 mg L⁻¹ formalin caused DO to decline from 9.0-10.0 to 6.0-8.1 mg L⁻¹ and pH from 7.0-7.3 to 5.9-6.6 within 72 h. Total ammonia-nitrogen increased over 72 h in ponds treated with 30 or 40 mg L⁻¹ formalin. Fish became re-infested with L. bidyana in all ponds within 30 days of treatment. A concentration of 30 mg L⁻¹ formalin is recommended as a treatment for monogeneans on silver perch in ponds, but aeration is necessary to maintain adequate water quality at higher temperatures.
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