Physiological effects of waterborne lead exposure in spiny dogfish (Squalus acanthias)

To broaden our knowledge about the toxicity of metals in marine elasmobranchs, cannulated spiny dogfish (Squalus acanthias) were exposed to 20μM and 100μM lead (Pb). Since we wanted to focus on sub lethal ion-osmoregulatory and respiratory disturbances, arterial blood samples were analysed for pH_a, PaO₂, haematocrit and total CO₂ values at several time points. Plasma was used to determine urea, TMAO, lactate and ion concentrations. After 96h, Pb concentrations were determined in a number of tissues, such as gill, rectal gland, skin and liver. To further investigate ion and osmoregulation, Na⁺/K⁺-ATPase activities in gill and rectal gland were analysed as well as rates of ammonia and urea excretion. Additionally, we studied the energy reserves in muscle and liver. Pb strongly accumulated in gills and especially in skin. Lower accumulation rates occurred in gut, kidney and rectal gland. A clear disturbance in acid-base status was observed after one day of exposure indicating a transient period of hyperventilation. The increase in pH_a was temporary at 20μM, but persisted at 100μM. After 2 days, plasma Na and Cl concentrations were reduced compared to controls at 100μM Pb and urea excretion rates were elevated. Pb caused impaired Na⁺/K⁺-ATPase activity in gills, but not in rectal gland. We conclude that spiny dogfish experienced relatively low ion-osmoregulatory and respiratory distress when exposed to lead, particularly when compared to effects of other metals such as silver. These elasmobranchs appear to be able to minimize the disturbance and maintain physiological homeostasis during an acute Pb exposure.