ASPHYXIATION POINT DETERMINATION OF SOME FARMFISHES

Asphyxiation points were determined under various experimental conditions for the fingerlings of four of our farmfishes,Hypophthal- michthys molitrix,Aristichthys nobilis,Mylopharyngodon piceus and Ctenopharyngodon idellus,commonly reared in mixed population in our fishponds.It was found that at a temperature of 23-24℃ these fingerlings manifest phenomena of suffocation when the dissolved oxygen content drops to the range as low as 0.23-0.99 mg per liter.Rising content of dissolved free carbon dioxide causes no appreciable effect on oxygen utilization,even at 32℃,provided that its concentration is kept within 30 mg/l,and for Aristichthys nobilis at least,within 60 mg/l;but ill effect is distinctly shown when it rises above 80 mg/l,even though the dissolved oxygen content in the meantime remains fairly high (4.34-6.56 mg/l).