Exposure to formaldehyde at therapeutic levels decreases peripheral blood lymphocytes and hematopoietic progenitors in the pronephros of tilapia Oreochromis niloticus

Abstract

Formaldehyde (HCHO) was recently detected at concentrations above the cancer benchmark in 90% of 60 000 surveyed United States census tracks. Formaldehyde leaches into and mixes with water extremely well, exposing aquatic life. Further, formaldehyde is used therapeutically in aquaculture to remove external protozoa and other parasites from fish. The present study was undertaken to determine if sub-acute HCHO causes immunologic changes in tilapia Oreochromis niloticus. Fish were exposed to 0, 50, or 150 ppm of HCHO. Immune parameters examined included blood hematology, spleen/body weight ratio, spleen and pronephros total cellularity, leukocyte blastogenesis, and natural killer cell cytotoxicity. Organ/body weight ratios and total cellularity were not different from controls. Similarly, mitogen response and natural killer cell function were unchanged. Peripheral blood lymphocytes decreased as HCHO exposure increased. Formaldehyde exposure also decreased the number of progenitor cells in the fish pronephros. These observations suggest possible immunosuppressive effects of HCHO in fish.