Low-salinity stress in the American lobster,Homarus americanus, after chronic sublethal exposure to cadmium: Biochemical effects

Abstract

Lobsters(Homarus americanus) were exposed to cadmium (6µg l−1, 30 days) in flowing seawater, then held for 7 days in aerated “clean ” seawater at either ambient (27 ‰) or low (17 ‰) salinity. Cadmium exposure alone (ambient salinity) induced a general elevation of enzyme activity (heart, antennal gland, and muscle MDH; heart LDH and GPI), despite the probability of some clearance of cadmium from body tissues during the “clean ” seawater holding period. Low-salinity alone (non-exposed lobsters) caused a decrease of enzyme activity (AAT, LDH, GPI, PK) in most tissues examined, except for tail muscle IDH, the activity of which was increased, and MDH, which was significantly elevated above ambient controls in all tissues except heart. Most low-salinity effects were observed in tail muscle, and most cadmium effects, in heart; low-salinity effects outnumbered cadmium stress by nine to four. In heart and tail muscle of cadmium-exposed lobsters held at low salinity, each of the two stresses apparently operated to nullify the other's effects. The most prominent single biochemical response to these sublethal stresses was the elevation of MDH activity. The ratio MDH: LDH gave the clearest indication of overall relative stress.