Effects of ambient and dietary cadmium on haematological parametres in Oreochromis mossambicus acclimatised to low- and high-calcium water

Bioaccumulation and Bioremediation of Heavy Metals in Fishes-A Review

Heavy metals, the most potent contaminants of the environment, are discharged into the aquatic ecosystems through the effluents of several industries, resulting in serious aquatic pollution. This type of severe heavy metal contamination in aquaculture systems has attracted great attention throughout the world. These toxic heavy metals are transmitted into the food chain through their bioaccumulation in different tissues of aquatic species and have aroused serious public health concerns. Heavy metal toxicity negatively affects the growth, reproduction, and physiology of fish, which is threatening the sustainable development of the aquaculture sector. Recently, several techniques, such as adsorption, physio-biochemical, molecular, and phytoremediation mechanisms have been successfully applied to reduce the toxicants in the environment. Microorganisms, especially several bacterial species, play a key role in this bioremediation process. In this context, the present review summarizes the bioaccumulation of different heavy metals into fishes, their toxic effects, and possible bioremediation techniques to protect the fishes from heavy metal contamination. Additionally, this paper discusses existing strategies to bioremediate heavy metals from aquatic ecosystems and the scope of genetic and molecular approaches for the effective bioremediation of heavy metals.

The toxicity of cadmium (Cd²⁺) towards embryos and pro-larva of soldatov's catfish (Silurus soldatovi)

A six-day static-renewal toxicity test was performed to determine the influences of cadmium on the development of embryos of soldatov's catfish (Silurus soldatovi). The median lethal concentration (LC50) value and median effective concentration (EC50, i.e., the total adverse effects, including developmental defects and mortality) were calculated to be 2740 and 133 μg/L, respectively, when cadmium was prepared in dilution water. The LC50 decreased to 266 μg/L in a subsequent test one month later, thereby suggesting that the sensitivity of this fish to cadmium in the early life stage(1) was largely influenced by the quality of fertilized eggs, which is known to be dependent on the season. The mortality and total adverse effects showed a concentration-dependent relationship at dosages greater than 1000 or 10 μg/L (p<0.05), respectively, at pro-larva stage (i.e., 144 hpf) with dilution water. To compare the toxic effects of cadmium under field and experimental conditions, filtered river water was adopted as a solvent simultaneously compared with dilution water. No significant differences were observed in mortality rate, hatching rate and adverse effect prevalence between the two solvents. In comparison to previously published toxicity data for other fish, the pro-larva of soldatov's catfish were less sensitive than established test fish in the early life stage. Therefore, the environmental risks would be overestimated when considering only existing toxicity data for other test fish.