Temperature effects on the blood oxygen affinity in sharks.

In fish, regional endothermy (i.e., the capacity to significantly elevate tissue temperatures above ambient via vascular heat exchangers) in the red swimming muscles (RM) has evolved only in a few marine groups (e.g., sharks: Lamnidae, Alopiidae, and teleosts Scombridae). Within these taxa, several species have also been shown to share similar physiological adaptations to enhance oxygen delivery to the working tissues. Although the hemoglobin (Hb) of most fish has a decreased affinity for oxygen with an increase in temperature, some regionally endothermic teleosts (e.g., tunas) have evolved Hbs that have a very low or even an increased affinity for oxygen with an increase in temperature. For sharks, however, blood oxygen affinities remain largely unknown. We examined the effects of temperature on the blood oxygen affinity in two pelagic species (the regionally endothermic shortfin mako shark and the ectothermic blue shark) at 15, 20, and 25 °C, and two coastal ectothermic species (the leopard shark and brown smooth-hound shark) at 10, 15, and 20 °C. Relative to the effects of temperature on the blood oxygen affinity of ectothermic sharks (e.g., blue shark), shortfin mako shark blood was less affected by an increase in temperature, a scenario similar to that documented in some of the tunas. In the shortfin mako shark, this may act to prevent premature oxygen dissociation from Hb as the blood is warmed during its passage through vascular heat exchangers. Even though the shortfin mako shark and blue shark occupy a similar niche, the effects of temperature on blood oxygen affinity in the latter more closely resembled that of the blood in the two coastal shark species examined in this study. The only exception was a small, reverse temperature effect (an increase in blood oxygen affinity with temperature) observed during the warming of the leopard shark blood under simulated arterial conditions, a finding that is likely related to the estuarine ecology of this species. Taken together, we found species-specific differences in how temperature affects blood oxygen affinity in sharks, with some similarities between the regionally endothermic sharks and several regionally endothermic teleost fishes.

Ozonation of aqueous solution containing bisphenol A: effect of operational parameters.

The degradation of bisphenol A (BPA) in aqueous solution by ozonation was studied. The study was conducted experimentally in a semi-batch reactor under different operational conditions, i.e., varying influent ozone gas concentration, initial BPA concentration, pH, and bicarbonate ion concentration. The results of the study indicated that ozonation could be used to effectively remove BPA from contaminated water. Keeping other operational parameters constant, the rate of BPA degradation linearly increased with ozone dosage. At pH value of 7.0, the second-order rate constants for the reaction of BPA with aqueous ozone were determined as 1.22 x 10(5), 1.71 x 10(5), and 2.59 x 10(5)M(-1)s(-1) for ozone gas dosages of 1.4, 2.2, and 5.1 mg L(-1), respectively. Bicarbonate ion in the range of 1.0-8.0 mM (61-488 ppm) showed no significant effect on BPA degradation for concentrations of BPA used in the study (23.0-57.0 microM). It was also observed that the rate of BPA degradation increased with pH up to 7.0, resulting in rate constants of 0.48 x 10(5), 0.94 x 10(5), and 1.71 x 10(5)M(-1)s(-1) at pH values of 2.0, 5.0, and 7.0, respectively; and the rate constant decreased to 1.16 x 10(5)M(-1)s(-1) at pH of 10.0.

Cortisol response of green sturgeon to acid-infusion stress.

Cortisol and lactate are classic indicators of stress in fishes and their interactive effects on metabolism during recovery from stress have recently become a subject of more intense study. We examined how stressing green sturgeon through acid infusion affected the cortisol response and lactate metabolism in green sturgeon (Acipenser medirostris). Both lactic acid (0.3 M) and HCl (0.3 N) infusion (infusion volumes 1.5 ml kg(-1)) elicited an immediate cortisol response (21.61+/-4.61 ng ml(-1) and 17.50+/-3.00 ng ml(-1), respectively). Lactic acid prolonged the cortisol response compared to HCl (90 min vs. 25 min). Neutralized lactate (0.23 M; with 1 N NaOH; final pH 7.8) and NaCl (0.9%) infusion (infusion volumes 1.5 ml kg(-1)) did not affect plasma cortisol. Sturgeon infused with lactic acid showed a faster rate of lactate disappearance from plasma than those with neutralized lactic acid. We relate these findings to lactate metabolism following exercise, acid-infusion and air immersion stress in fishes.