The effect of levothyroxine sodium hormone on percentage of hatching and survival rate and the early growth stage of Oncorhynchus mykiss larvae

levothyroxine sodium hormone has a special relationship with early stages of growth, development and survival fish larvae. The present study investigated the effect of levothyroxine sodium hormone on percentage of hatching and survival rate and the early growth stage of rainbow trout (Oncorhynchus mykiss) larvae. This study was carried out in Dalkhan propagation and cultivation farm, Sepidan, Shiraz. In order to find out the way of fertilized eggs that were bathed in levothyroxine sodium with concentrations of 0, 0.1, 0.5 and 1.0 mg/L (each one, triplicates) for six hours. Then they were transferred into troughf trays with running water. After hatching all larvae were placed in mentioned levothyroxine sodium concentration bath for another six hours into troughfs (without tray). Larvae stayed in troughfs until the yolk- sac was observed. Finally, live rainbow trout larvae were counted in seprated plates. Results of present study indicated that the highest ratio of hatched eggs (81.42%± 1.04) and survival larvae after the yolk – sac was observed (72.90%± 0.75) were observed in 0.5 mg/L of levothyroxine sodium concentration (P0.05).