Studies on some fish diseases caused by different toxic substances and organic wastes

In this study four experiments and field study were carried out, andthe results could be summarized as following:I. Nitrate toxicity in Tilapia fish:1- Acute toxicity:Mortality rate of Tilapia fish which exposed to different doses ofsodium nitrate recorded 0.00, 10, 50, 65, 95 and 100% at concentrationof 900, 1100, 1300, 1500, 1700 and 1900 mg/L of sodi urn nitraterespectively.The lethal concentration (96-hr LCso) was 1365 mg/L of sodiumnitrate {995.63 mg N03-NIL) during 96-hr.Clinical signs were in the form of nervous movements,spasmodically open of gill opercula and mouth, loss of equilibrium andfish lies on its side until death.Postmortem: congestion of all internal organs (liver, spleen andkidney) and also the gills were congested and contained considerableamount of mucous.2- Subchronic toxicity:Tilapia fish were exposed to various concentrations of nitrate (99.56and 199.12 mg N03-N/L) which equal to 1110 and 115 LCso of nitrate for .