of Formalin and Sodium Chloride

Abstract.—The purpose of this study was to determine the tolerance of larval fish in the families Characidae, Cyprinidae, and Belontiidae to therapeutic doses of sodium chloride and formalin. Four species of fish were included in this study: zebra danio Brachydanio rerio (also known as Danio rerio), black tetra Gymnocorymbus ternetzi, Buenos Aires tetra Hemigrammus caudovittatus, and blue gourami (also known as threespot gourami) Trichogaster trichopterus. Representative species from each family for both yolk sac fry (2–3 d old) and free-swimming fry (5–7 d old) were tested. The treatments consisted of 1 or 3 g/L sodium chloride or 12.5 or 25 mg/L formalin. Mortalities at 24 and 48 h were compared. Although 12.5–25 mg/L of formalin appears to be safe for very young zebra danio fry, therapeutic doses of salt are not recommended. Yolk sac and free-swimming fry of the blue gourami are tolerant of therapeutic doses of salt (1–3 g/L) but very sensitive to formalin. Because there are significant differences in the tolerance of black tetras and albino Buenos Aires tetras to salt and formalin, neither treatment is recommended for use with the yolk sac and free-swimming fry of these species. Many species of freshwater ornamental fish are cultured in the United States, primarily in Florida