African Journal of Aquatic Science

Log in or Register to get access to full text downloads.

Remember me or Register

DOWNLOAD FULL TEXT Open Access  DOWNLOAD FULL TEXT Subscription or Fee Access

The effects of lead, water hardness and pH on oxygen consumption, plasma chlorides and bioaccumulation in the freshwater fish Tilapia sparrmanii

WJ van Aardt, LCR Venter


Closed system
respirometry was performed on captive juvenile Tilapia sparrmanii
exposed for 96 hours to a range of Pb-acetate concentrations in hard and soft
water to determine the effect of Pb in relation to water hardness and pH. For
hard and soft water with a pH above 7.51 no change in the resting specific
oxygen consumption rate (MD7 O2) was found when the fish
were exposed to nominal concentrations of 1, 5, 10, or 20mg Pb l–1
normoxic water. In soft, acidic normoxic water (pH 6.28) containing 10mg l–1
Pb- acetate, MD7 O2 increased significantly (P < 0.05)
above normal values from 4.38 to 6.36 B1 0.9mmol O2 kg–1
fish h–1. In progressive anoxic water (PO2 from 130mm Hg
to 15mm Hg) resting MD7 O2 decreased by nearly 85%
compared with normoxic conditions. This decrease seemed not to be influenced by
acute Pb-acetate exposure but to be due to acute oxygen deprivation. Handling
(transport from maintenance tanks to respirometers) increased the MD7
O2 by 35%, but this decreased to normal levels (4.38 B1 0.41mmol O2
kg–1 fish h–1) for a standardised (30 gram) fish four to
six hours after handling. The percentage of Pb in solution 96 hours after
application, decreased linearly in a range of soft to hard water types to less
than 1%. Contrary to that in hard water, in soft water, with a pH of 6.28 a
significant (P < 0.05) decrease in plasma chlorides (from 144.5mmol Cl to
111.9mmol Cl) was measured in 10mg Pb l–1 water while a significant
increase in soluble blood plasma solids (from 5.68g 100ml–1 to 7.14g
100ml–1) was found. No change in bile solids was found for fish
exposed to lead ranging from 1–20mg Pb l–1 in soft or hard alkaline
water or soft acidic water.

It is concluded that resting MD7
O2 and blood chloride values are not influenced by acute Pb
concentrations (10 and 20mg l–1) in hard water or soft alkaline
water, but that this changes significantly in acidic soft water and may be used
as a biomarker in short term (96h) exposure experiments. Progressive anoxia
combined with lead exposure further reduces the ability of the gill epithelium
to take up oxygen.

Precipitated lead in water bodies may
potentially be a health hazard for aquatic organisms if it dissolves from the
sediment at low pH.

African Journal of Aquatic Science
2004, 29(1): 37–46
AJOL African Journals Online