Temperature
Fish and crustaceans are poikilothermic or "cold-blooded". This means that their body temperature is roughly the same as the temperature of the water surrounding them. Of course, water temperature changes daily and seasonally, so the body temperature of fish and crustaceans changes frequently. The rates of biochemical processes are temperature dependent. Under natural conditions, low temperature appears to be a greater cause of penaeid mortality than high temperature. The upper median lethal temperature of juveniles penaeids are mainly around 34-36°C. Optimal growth rates for P. japonicus are at temperatures between 25 to 30oC. Growth stops and feeding ceases at under 12 to 15oC, while temperatures as low as 4oC can be tolerated for short periods of time (Dall et al., 1990).

While high lethal temperatures may occur in tropical estuaries, in most areas it is the inhibition of growth and increase of mortalities by reduced temperatures which must be dealt with. Freezing temperatures can be tolerated by Gulf Coast shrimp for extended periods of time only if the shrimp are given the appropriate burrowing conditions (Hanson & Goodwin, 1977).

Temperatures required for optimum or maximum growth differ between species. P. japonicus, common in Asian waters, dwells in coastal waters of moderate temperature, and the adults are not found in mangrove swamps. P. monodon is a tropical Indo-Pacific species which endures high temperatures and often penetrates into rivers and milkfish ponds (Shigueno, 1975).

Temperature - Salinity interactions

Postlarval and juvenile penaeids live in inshore habitats where extremes of temperature can occur simultaneously with low salinity. Salinity stress can affect temperature tolerance. The postlarvae of P. aztecus have a significantly greater resistance to high temperature when tested at 25‰ than at either 15‰ or 5‰. Acclimation at low salinity modifies the salinity effect on temperature tolerance markedly and postlarvae acclimated at 5‰ are more resistant than those acclimated in higher salinities (Dall et al., 1990).