Survey results of four Metro Manila wet markets revealed that both fresh and salt water fish analyzed were positive for formaldehyde. It was thus probable that all fish dealers practice formalin treatment.The study showed that as short as 15 minutes soaking time of fish in 1,000 ppm formalin solution resulted to 36 percent increase in formaldehyde residue. It was also found that the texture of fish was affected by formalin treatment. Consumers therefore will be deceived by the firmness of the fish even if the products have been exposed in the market for prolonged periods of time.This study also revealed that formaldehyde residues in fish even as low as 5.3 ppm caused the death of test mice as revealed in the toxicity test and that soaking of fish to as high as 2,000 ppm formaldehyde up to 45 minutes did not inhibit the growth of salmonella, a public health significant organism found in fish moreover, no off flavor due to formaldehyde was detectable and cooking did not destroy the formaldehyde residues present in fish.
The project aims to determine the extent of use and method of application of formalin as a disinfectant by local fish dealers and to determine the safety and efficacy of formalin as a preservative. The project also intended to determine the levels of formaldehyde residue and toxicity levels in formalin treated fish and the effect on cooked fish.