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The oxygen consumption of common carp and rainbow trout larvae exposed to mercury, cadmium and copper was measured. The experiment was performed on seven-month-old common carp (0.9-1.39 g) and one-month-old rainbow trout larvae (1.2-1.5 g) reared under laboratory conditions. The fish were treated for one hour with solutions of a single metal or mixtures of Hg+Cd, Cd+Cu or Hg+Cu. The concentrations of single metals or mixtures were 0.025,0.05,0.1 and 0.2 mg l⁻¹. Both single metals and mixtures reduced oxygen consumption in a concentration-dependent way. The results indicate that the oxygen consumption rate is a reliable indicator of metal toxicity to fish. The levels of oxygen consumption decrease indicate that the rankings of metal toxicity for the given nominal trace metal concentration are Hg+Cu > Cu > Cd+Cu > Cd+Hg > Cd for common carp and Hg+Cu > Cu > Cd+Hg > Hg for rainbow trout. The results show that copper is most toxic to both fish species. The mixtures are more toxic than single metals are and cause a greater reduction in oxygen consumption. Common carp larvae are apparently more sensitive to cadmium, while rainbow trout is more sensitive to mercury.
The sperm collected from common and grass carp males was stored at 5oC, and activated with water of various temperatures (20, 26, and 30oC). Time of spermatozoa motility was measured. Motility decreased with time after milt collection. Common carp spermatozoa were active longer, up to 70–80 s. In most series their activity was reduced after 24 hours. Spermatozoa of grass carp were active up to 30–55 s, and their motility shortened already in 8 hours post collection. After 24 hours they were motile less than 10 s. The effect of temperature of activation was observed – the spermatozoa were active for the longest time at 20oC. Spermatozoa motility time was also affected by temperature of storage. Even short–term (15 min) keeping spermatozoa at 20oC shortened their motility time in both species, and after 2 hour storage common carp sperm motility was reduced by about 50%.
The study was conducted on common carp and grass carp embryos and larvae developed under laboratory conditions, at various temperatures and in the presence of heavy metals (Cu 0.20-0.27 mg dm⁻³ , Pb 2.0-4.0 mg dm⁻³ , Cd 0.2 mg dm⁻³ ). Heart rate was measured at various developmental stages and was observed to increase along with fish development in all experimental groups. This may be explained by the increase in the metabolic rate of developing embryos. Development was faster at higher temperatures, and the heart rate was usually higher. The results of the present study confirm that heart rate is a reliable indicator of the metabolic rate of developing fish embryos.The embryos and larvae which were exposed to heavy metals had higher heart rates in comparison to those of the control group. This indicates that metal-induced stress caused an increase in metabolic rate. A decrease in heart rate during hatching was observed at non-optimum temperatures and was particularly pronounced in metal-exposed embryos; this indicates that the disturbances were related to the high sensitivity of the fish at this stage.
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