3-Trifluoromethyl-4-nitrophenol (TFM) toxicity and UDP-glucuronyltransferase kinetics in three bullfrog life stages and fish, with relevance to warmwater aquaculture

Abstract

The purpose of this research was to examine the basis for the selective toxicity of 3-trifluoromethyl-4-nitrophenol (TFM) in different bullfrog life stages and fish, and to document the extent to which tadpole infestation is a problem in warmwater aquaculture. Kinetics of the biotransformation enzyme UDP-glucuronyltransferase (UDPGT) were examined in hepatic microsomal preparations from bullfrog larvae and adults, and four species of fish. A survey was conducted in Florida and Arkansas to evaluate the effect of tadpole infestations on warmwater fish pond culture. Tadpole infestation was deemed a serious problem, primarily due to competition between tadpoles and fish for food. Tadpoles also caused harvest problems and made fish production more labor intensive. Annual loss of ornamental fish in Florida and baitfish in Arkansas due to tadpole infestations was estimated at {dollar}1.78 million and \{dollar}6.2 million, respectively. Toxicity of aqueous TFM to bullfrog larvae was an order of magnitude greater than in bullfrog adults (LC{dollar}\sb{lcub}50{rcub}{dollar}s = 0.95 and 12.99 mg/L, respectively). However, larvae and adults had similar sensitivity to TFM exposed by intraperitoneal route (LD{dollar}\sb{lcub}50{rcub}{dollar}s = 11.62 and 15.35 mg/kg, respectively). Frog egg development was arrested by TFM at concentrations {dollar}\ge{dollar}1.0 mg/L. TFM-UDPGT kinetics in bullfrog larvae and adults differed significantly ({dollar}P<0.05{dollar}). V{dollar}\sb{lcub}\rm max{rcub}{dollar} for TFM-UDPGT in bullfrog larvae and adults was calculated to be 1.05 and 2.45 nmol/min{dollar}\cdot{dollar}mg, respectively; K{dollar}\sb{lcub}\rm m{rcub}{dollar} for bullfrog larvae and adults was 38 and 64 {dollar}\mu{dollar}M, respectively. However, V{dollar}\sb{lcub}\rm max{rcub}{dollar}/K{dollar}\sb{lcub}\rm m{rcub}{dollar} did not significantly differ between the two life stages. For the fish species examined, V{dollar}\sb{lcub}\rm max{rcub}{dollar} for TFM-UDPGT activity was significantly greater (p {dollar}<{dollar} 0.05) in bluegill (1.52 {dollar}\pm{dollar} 0.10), trout (1.82 {dollar}\pm{dollar} 0.22) and channel catfish (1.46 {dollar}\pm{dollar} 0.07) than in lamprey (0.68 {dollar}\pm{dollar}.010). K{dollar}\sb{lcub}\rm m{rcub}{dollar} was primarily responsible for differences in V{dollar}\sb{lcub}\rm max{rcub}{dollar}/K{dollar}\sb{lcub}\rm m{rcub}{dollar} for TFM in lamprey (0.0037 {dollar}\pm{dollar} 0.0002), channel catfish (0.0107 {dollar}\pm{dollar} 0.005), trout (0.0189 {dollar}\pm{dollar} 0.0018) and bluegill (0.0281 {dollar}\pm{dollar} 0.004). These ratios appear progressively lower in species which are more sensitive (i.e., lower LC{dollar}\sb{lcub}50{rcub}{dollar}s) to aqueous TFM. Data from the survey indicated that tadpole infestations caused severe economic damage and impaired production in warmwater fish pond culture. Based on laboratory data from this and other studies, greater sensitivity to aqueous TFM in gill-respiring bullfrog larvae (compared with adults) does not primarily appear to be a function of differences in UDPGT-mediated metabolism, but rather may reflect differences in other processes such as uptake. In fish, however, UDPGT kinetics, particularly K{dollar}\sb{lcub}\rm m{rcub}{dollar}, correlated well with in vivo sensitivity to TFM.