Effects of Sodium Pentachlorophenate and 2,4-Dinitrophenol on Respiration in Crustaceans

Abstract

The oxygen consumption of the grass shrimp, Palaemonetes pugio, was determined at different stages of the molt cycle. At each stage of the molt cycle, the oxygen consumption varied in relation to periods of activity. In order to minimize the errors in establishing basal (control) rates of oxygen consumption, measurements were made over extended periods (18 to 24 hours). In contrast to the previous reports of progressive increases in oxygen consumption during proecdysial stages in other crustaceans, we noted significant increases in oxygen consumption just prior to and during the actual shedding of exoskeleton (ecdysis) in grass shrimp. The effects of sodium pentachlorophenate (Na-PCP) on oxygen consumption varied depending on the stage of the molt cycle, concentration of Na-PCP and extent of pre-exposure of shrimp to Na-PCP. At concentrations of 1.5 and 5.0 ppm, Na-PCP did not alter the oxygen consumption of shrimp in intermolt and proecdysial stages of the molt cycle. Late proecdysial shrimp exposed to 5.0 ppm Na-PCP exhibited an increase in oxygen consumption in relation to ecdysis to the same level as that of control shrimp. However, following ecdysis, the shrimp exposed to 5.0 ppm Na-PCP exhibited a dramatic decline in oxygen consumption and died within three hours. This increased sensitivity during the early postecdysial period appeared to be related to an increase in the uptake of Na-PCP at this stage compared to intermolt and proecdysial stages. A decline in oxygen consumption as noted above could be induced in intermolt shrimp by using higher concentrations of Na-PCP. Exposure of shrimp to 10 or 20 ppm Na-PCP, or to 5 ppm followed by 20 ppm Na-PCP caused an initial increase in oxygen consumption and a subsequent decline leading to death. The survival time of intermolt shrimp pretreated with 5 ppm Na-PCP was longer than that of shrimp exposed directly to 10 or 20 ppm Na-PCP. Although 20 ppm 2,4-dinitrophenol (DNP) caused an initial increase in oxygen consumption in intermolt shrimp, this was not followed by any decline in oxygen consumption or death during a 24-hour exposure.

The effects of Na-PCP and DNP on tissue respiration in vitro were studied using the blue crab, Callinectes sapidus. At concentrations of 1 × 10⁻⁶ M and 5 × 10⁻⁵ M, these compounds did not alter the oxygen consumption of the muscle, gill and hepatopancreas. At a concentration of 5 × 10⁻³ M, both Na-PCP and DNP caused an inhibition of oxygen consumption of isolated tissues.