Copper Homeostasis and Toxicity in the elasmobranch Raja erinacea and the Teleost Myoxocephalus octodecemspinosus During Exposure to Elevated Water-Borne Copper

Clear nosed skate, Raja erinacea were exposed to 0.10 (control), 0.52 or 1.73
mM copper and sculpin, Myoxocephalus octodecemspinosus were exposed to 0.10 or
1.73 mM copper (as CuSO ) in Salisbury Cove seawater for up to seven days.
Skate gill copper concentrations increased 40-50 fold over background in
response to copper exposure at both concentrations. In comparison, sculpin gill
levels only increased 3-fold. While there was no evidence for internalized
copper in the skate arising from the water-borne exposure, sculpin kidneys, but
not livers, exhibited elevated copper concentrations after the seven days of
exposure. The marked difference in branchial copper accumulation between the
skate and the sculpin likely explains why elasmobranchs appear to be more
sensitive to metal exposure than most marine teleost fish. Brain tissue from
both species and the skate rectal gland contained relatively high background
copper concentrations. Copper exposure caused an initial transient reduction in
skate plasma total ammonia (T amm), but eventually led to elevated plasma T .
Despite the marked branchial copper accumulation in the skate, there was no
reduction in amm gill NayK-ATPase activity. Similarly, NayK-ATPase activity in
skate rectal gland and intestine, as well as in sculpin gill and intestine were
not affected by copper exposure. Plasma sodium, magnesium and chloride were not
affected by copper exposure in either the skate or the sculpin. We set out to
compare copper uptake and distribution in an elasmobranch, the clear nosed
skate (Raja erinacea) and a teleost, the sculpin (Myoxoce- phalus
octodecemspinosus). Suspecting osmoregulatory disturbance as the main toxic
mechanism of copper to both species various osmoregulatory endpoints were
considered. In addition, plasma ammonia (Tamm ) was measured, because one of
the most consistent effects of copper exposure in freshwater fish is elevated
plasma ammonia (Lauren and McDonald, 1985; Wilson and Taylor,1993b; Beaumont et
al., 1995; De boeck et al., 1995; Wang et al., 1998) due to a combined
increased production and possibly impaired branchial clearance (Grosell et al.,
2002).