Postlarvae of two species of penaeid shrimp, Penaeus aztecus and P. setiferus, were exposed to varying temperatures under controlled conditions. P. aztecus regularly burrowed into the silty clay substrate as the temperature fell to 12-17°C, and emerged as the
temperature rose to 18-21.5°C. Under identical conditions, P. setiferus showed neither type of activity. Burrowing in response to low temperature is interpreted as a behavioral mechanism having survival value in the northwestern Gulf of Mexico for P. aztecus, which is
known to reach estuarine areas early in the year, when bay waters are often cold. Such a mechanism would be less useful to P.setiferus, which usually arrives at bays during the summer. The temperatures which stimulated burrowing of the postlarvae of P. aztecus in the laboratory
are comparable with natural water temperatures off the Texas and Louisiana coasts during the winter. Furthermore, the temperature range which stimulated emergence of this organism from the substrate in the laboratory is quite similar to that associated with the appearance of most postlarvae
of P. aztecus at bays. These findings support the hypothesis that most postlarvae of this shrimp species hibernate in the burrowed condition for at least a portion of the winter in the northwest Gulf of Mexico.
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