Heavy metals contamination is a serious problem in the aquatic environment. Some of them are very important, having biological roles for aquatic organisms, and called essential heavy metals. In contrast, other heavy metals are considered harmful even at low concentrations. The toxic levels of heavy metals may be of agricultural, industrial and mining activities. This will cause water pollution and changes in the physicochemical characteristics of the aquatic environment. This pollution has deleterious toxic effects on fish and raises concerns over its potential impact on human health. The most common heavy metals are arsenic, chromium, lead and mercury, which affect human health and are considered systemic toxicants. These metals induce organ damage even at low levels of exposure and according to the US Environmental protection agency and international agency for research on cancer, they classified as carcinogens. For all the above reasons, this review was written to contribute to heavy metals' role in the environment, toxic mechanism and toxic effects on fish.

Coronaviruses are large, enveloped and single-stranded, non-segmented with positive sense RNA virus belong to Nidovirus, family Coronavirirdae and included two subfamilies Orthocoronavirinae and Letovirinae. There are four genera variable in antigenestic characteristic and cross-reactivity (Alpha-coronavirus, Beta-coronavirus, Gamma-coronavirus and Deltacoronavirus) affect mammals and birds while Bafinivirus affect fish and cause different diseases in the vertebrate animals and human, so this review listed most important diseases in some animals which cause economic problems as in the avian cause infectious bronchitis(IB), in the bovine cause diseases in both bowl and respiratory system, Enteric form Disease in the equine, two forms of diseases have been occurred in the feline (feline enteric coronavirus and feline infectious peritonitis), in canine cause enteric and respiratory syndroms while in the porcine the diseases occur as are Transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhoea virus (PEDV), and porcine deltacoronavirus (PDCoV).Also corona viruses affect aquatic animals and cause general clinical signs in fish. Some of these pathogens transmitted from camel and bates and causes diseases for human as SARS, MERS and SARS-2.From these review the conclusion is the hygiene practices and biosecurity are more important to prevent the emerging diseases in both human and animals cause by coronavirus.