Residual Formaldehyde in the Tissues of Formalin-treated Rainbow Trout, Oncorhynchus mykiss

Abstract

The uptake and transport of formaldehyde in the tissues of rainbow trout exposed to 250 ppm formalin for 1 or 4.5 h were investigated. In the 1 h treated fish, neither a marked rise in concentration of formaldehyde, nor a differential value between mature and immature fish was observed. Moribund fish in the 4.5 h treated group showed relatively high concentration of formaldehyde in blood, liver and kidney, but recovery required only a few days. In each treatment a very small amount of formaldehyde was detected in the muscle. Formaldehyde in liver and kidney was supposed to be supplied by the blood through the gill and that in muscle merely by the permeability of the skin.
Thus, treating the fish with formalin for 1 h at 250 ppm, in order to control the external parasites of rainbow trout resulted in a little residual formaldehyde in the blood, liver, kidney and muscle, which could not be in conflict with the specifications of the Food Sanitation Law.