Marine teleostean fish are hypo‐osmotic to seawater. As part of a multiorgan osmoregulatory strategy they drink seawater and selectively absorb water and minerals across the intestinal epithelium. Notably, divalent cations (Ca2+ and Mg2‒) are left behind. We report here that in the gulf toadfish, Opsanus beta, the ionic by‐products of osmoregulation in the intestine contribute to de novo formation of a carbonate mineral, tentatively identified as calcian kutnohorite. Our data suggest that intestinal mineralization is a general feature of osmoregulation in marine teleosts and that this process is an unrecognized and possibly substantial source of marine carbonate sediments.

Gulf toadfish, Opsanus beta, were exposed to initial [ i4C]benzo[a]pyrene (BaP) concentrations of 5pg/L in a simple static system at high and low temperatures (18 or 28°C) following long-term (>4 weeks) acclimation to these temperatures or an acute temperature change (18 to 28°C or 28 to 18°C) to assess the effects of temperature on the uptake and disposition of BaP. BaP uptake was estimated from the disappearance of BaP from the water. Uptake rates estimated at initial BaP concentrations for the four temperature treatments (acclimation temperature:exposure temperature), 28:18, 28:28, 18:18 and 18:28"C, were 0.020 * 0.001, 0.051 * 0.005, 0.031 k 0.004 and 0.065 * 0.004 pg BaP/g body weight/h (~s E , N = 6). The decrease in BaP uptake with decreasing BaP concentration indicates that BaP uptake is directly proportional to the concentration in water, and calculated Qlo values suggest that uptake is modulated by temperature-induced changes in respiration rate or convection volume. BaP was detected in all tissues examined, with the highest levels in the bile, the liver, the kidney and the gills. Greater uptake rates of carcinogens such as BaP at higher temperatures may in part explain higher rates of tumor formation in fish exposed to carcinogens at high temperatures.

Prior in vivo studies of the effects of temperature on uptake, metabolism and excretion of benzo[a]pyrene (BaP) by the gulf toadfish (Opsanus beta) suggested that metabolism of BaP may be partially temperature insensitive under certain conditions. In the present study, hepatocytes were isolated from toadfish acclimated to 18 or 28 °C, and then cells were exposed to BaP at 18, 23, and 28 °C in vitro to more directly examine the effects of temperature on metabolism. Toadfish hepatocytes metabolized BaP to a variety of Phase I and Phase II metabolites in similar proportions to toadfish in vivo, with the exception that fewer Phase I metabolites were detected. A marked temperature dependence of metabolism of BaP to Phase II metabolites was noted between 18 and 28 °C at near saturating concentration of BaP (13 μg∙mL−1). Warm-acclimated toadfish displayed a lower temperature sensitivity than cold-acclimated toadfish (Q10, the ratio of the rate at T + 10 °C: rate at T = 1.85 and 2.65, respectively). However, at a lower, subsaturating concentration of BaP (5 μg∙mL−1), production of all metabolites showed a marked temperature independence. We speculate that this independence is the result of temperature effects on the kinetic properties of the enzymes of xenobiotic metabolism.

Changes in cytochrome P-450 and microsomal and soluble protein content and the activities of several microsomal and cytosolic xenobiotic metabolizing enzymes were examined in the whole livers of gulf toadfish, Opsanus beta, following acclimation to 18 or 28 °C and in isolated hepatocytes (prepared from 18 or 28 °C acclimated gulf toadfish) which were maintained in primary culture for 29 d on L-15 media. Cells isolated from both acclimation groups were cultured at 18 and 28 °C. In whole livers, significant differences were found in the activities of sulfotransferase (which showed perfect compensation) and UDP-glucuronosyltransferase (which showed "inverse compensation") between fish acclimated to 18 and 28 °C, but several other trends were obscured by interindividual variation. However, in hepatocyte cultures, temperature adaptations were seen in cytochrome P-450 content and in the activities of the microsomal enzymes aryl hydrocarbon hydroxylase, epoxide hydrolase, and UDP-glucuronosyltransferase. Glutathione-S-transferase activity appeared to be rather temperature insensitive in both whole livers and in cultured hepatocytes. Incomplete temperature acclimation for all enzymes was observed in cultured cells and this may be due to systemic factors which were not present in cell culture media.

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