Salinity preference of postlarval brown and white shrimp (Penaeus aztecus & P. setiferus) in gradient tanks.

Brown and white postlarval shrimp (Penaeus aztecus and P. setiferus) were collected at the beachfront and tested at constant low level red illumination in tanks containing salinity gradients ranging from 0 to 50 ppt and 0 to 70 ppt and in control tanks having uniform salinity. Gradients were stable for as long as 119 hours with maximum deviations in salinity of 3 ppt. Generally, final gradient salinities were identical to initial gradient salinities or differed at a given point by only 1 or 2 ppt. Postlarvae of both species sought salinities lower than those generally found in the open Gulf of Mexico. It is suggested that post-larval shrimp orient to bays by utilizing natural salinity gradients that extend seaward from the estuaries. Proposed water diversion projects, such as the Texas Water Plan, would restrict or curtail fresh water inflow to the estuaries thereby altering natural gradients of both salinity and dissolved organics. This might affect the immigration of shrimp and other estuarine-dependent organisms to the estuaries.