Water hardness and the effects of Cd on oxygen consumption, plasma chlorides and bioaccumulation in <i>Tilapia sparrmanii</i>

Abstract

Closed system respirometry was performed on captive juvenile (30 ± 8 g; mean ± S.E.M) Tilapia sparrmanii exposed for 96 h to low (1 mg·l -1 ) and high (20 mg·l -1 ) levels of cadmium in soft and hard water. In hard water (235 mg·l -1 as CaCO 3 ), cadmium (Cd) applied as CdCl 2 , precipitates completely out but in very soft water (16.5 mg·l -1 as Ca CO 3 ), 23% of Cd is in solution 96 h after it was dissolved. Cadmium complexation is not caused by the presence of chlorides but probably depends on carbonates and sulphates present in Mooi River water. Handling stress, that lasts for at least 6 h, increased the specific oxygen consumption rate of T. sparrmanii (ΜO 2 ) by more than 30% compared to resting oxygen consumption levels. In hard water no change in the ΜO 2 was found when T. sparrmanii was exposed to 1, 5, 10, or 20 mg of Cd·l -1 of water. In soft alkaline water all fish died when exposed for 96 h in 20 mg Cd·l -1 . For 10 mg Cd·l -1 , the ΜO 2 was reduced significantly (p< 0.05) by 30%. The percentage cadmium dissolved in hard water was, after 96 h, below 1%, 96 h after it had been dissolved. About 2 000 µg Cd·g -1 accumulates per gram dried gill mass when fish are exposed to 20 mg Cd·l -1 in hard water. For soft water the Cd accumulation is about twice as much. In liver tissue more than 60 µg Cd accumulates per gram dried liver mass in hard water. In soft water the accumulation was three times as much. Blood plasma chlorides decreased from a mean of 130 mmol to 60 mmol when exposed to 20 mg Cd·l -1 in soft water. The differences were statistically significant (P< 0.05). No decrease in blood plasma chlorides was found in hard water when fish were exposed to 20 mg Cd·l -1 of water. Fish handling reduces the oxygen consumption rate by 35% but ΜO 2 returns to normal resting levels 6 h after handling stress. It is concluded from the results that ΜO 2 and blood chlorides can be used as parameters for Cd toxicity in a 96 h exposure period provided that the precipitation of Cd in the water is known and the pH of the water is monitored.

Metals Concentrations in Tissues of Tilapia gallier, Crarias lazera and Osteoglossidae Caught from Alau Dam, Maiduguri, Borno State, Nigeria

“…Many of the dissolved metals that enter rivers are adsorbed onto colloid particulates. Also at high alkalinity and pH, the metals, particularly lead and cadmium, precipitate by forming complexation dramatically influence metal toxicity [5,6] . Although many heavy metals are considered as essential macro and micro elements especially at non adverse effect levels [7,8] , they can exert toxic effects at concentrations encountered in polluted environment.…”

The effect of short-term Cu exposure on the oxygen consumption and Cu accumulation of mudfish (<i>Labeo capensis</i>) and the largemouth bass (<i>Micropteris salmoides</i>) in hard water

“…The sampler was operated from a boat and took sediment samples from about 2 m below the water surface. Each sample, with an average mass of 900 g, was taken from the core sampler, enclosed in its polyvinyl jacket, and air dried in a vertical position for 24 h (Van Aardt and Erdmann, 2004).…”

“…The fish were transported in a 400 ℓ container filled with aerated dam water and spiked with 12 g NaCl•ℓ -1 water (Walsh, 1984). At the fish plant the fish were treated with 2% formaldehyde and 33 mg malachite green•ℓ -1 for 10 s and transferred to the 5 000 ℓ fish-holding tanks (Van Aardt and Booysen, 2004). M. salmoides were fed earthworms or fish fry (Tilapia sparrmanii) from Boskop Dam.…”

“…The analysis protocols for Cu were the same as for the sediments except that the standard reference material used was (Dorm-2) from the National Research Council, Canada. To express the metal concentrations obtained from L. capensis per gram dried tissue, the percentage of water for each of the seven tissue types was determined as described by van Aardt and Erdmann (2004).…”

“…The average [Cu] in soils world-wide is 20 mg•kg -1 (Nriagu, 1979). In Labeo capensis, a mudfish from the Mooi River Dams, Van Aardt and Erdmann (2004) found 150 (±17.8) mg Cu•kg -1 and 130 (± 23.1) mg Zn•kg -1 in dried liver. Copper concentrations for relatively unpolluted water include a mean of 5 µg Cu•ℓ -1 for 'average river water' while the Amazon and its tributaries range from 0.3 µg•Cu•ℓ -1 to 2.3 µg Cu•ℓ -1 (Boyle, 1976;Kelly, 1988).…”