Detection of yellow-head disease in intensive freshwater production systems of Litopenaeus vannamei

The culture of penaeid shrimps in inland well waters with low salinity represents an important development in aquaculture. Yellow-head disease of shrimps has been reported in many countries in Asia and Latin America, but, in most cases, the etiologic agents have not been clearly defined. In the present study, we used reverse transcription-nested polymerase chain reaction (RT-n PCR) to detect yellow-head virus (YHV), white-spot syndrome virus (WSSV), and gill-associated virus (GAV), during single-culture cycles of Litopenaeus vannamei on two farms (F1 and F2), located in Colima, Mexico. The shrimps were intensively cultured in freshwater, with densities of 70 organisms (org) m(-2) and 25 org m(-2) and hardness values of 390 and 450 mg l(-1) (as CaCo3), respectively. The average salinities throughout the year were 0 ppm. The results obtained indicated that the samples were negative to WSSV and GAV. YHV was present on each farm, with a prevalence of 13%, over 60 days of observation. During this time, the growth of shrimps decreased on F1. The infections obeyed the principles of horizontal transmission, and we discuss various factors, such as increases in shrimp density and consequent lower levels of oxygen, that could increase the effects of YHV on the health of shrimps in farm F1.