Factors affecting the successful culture of Penaeus stylirostris and Penaeus vannamei at an estuarine power plant site : temperature, salinity, inherent growth variability, damselfly nymph predation, population density and distribution, and polyculture

Typescript (photocopy).Laboratory and pond research was conducted at a power plant site near the inner end of Galveston Bay, Texas. Of tested salinity levels, 25 ('o)/oo was found the best for both species to resist high lethal temperatures and to attain maximum growth and survival, while 5 ('o)/oo was extremely unfavorable, especially for Penaeus stylirostris. Upper incipient lethal temperatures obtained at 25 ('o)/oo salinity were between 37.0 and 38.0 C and between 38.0 and 39.0 C for both species acclimated to 25.0 and 30.0 C, respectively. They were 39.0 C and between 39.0 and 40.0 C, respectively, for Penaeus vannamei and P. stylirostris acclimated to 35.0 C. These figures are recommended as design criteria for shrimp mariculture systems, especially those which utilize heated effluents from power plants. The existence of an inherent growth difference among sibling shrimp was verified in both species. Possible underlying mechanisms such as competition, pheromone effect, and differences in locomotor and feeding activity were experimentally rejected. Monoculture of P. stylirostris in ponds at 7.5, 10, 15, and 20/m('2) and polyculture of that species with P. vannamei at two species stocking ratios (3:1 and 1:3) and a total density of 20/m('2) were also attempted. Yields ranged from 227 to 2,111 kg/ha. Monoculture yields of P. stylirostris at 20/m('2) averaged 1,409/ha, the highest reported for this species. In polyculture, the 3:1 ratio of P. vannamei to P. stylirostris was the better stocking strategy in terms of yield (averaging 1,968 kg/ha), and the only strategy indicated to be profitable by economical analyses. Winter maintenance of P. vannamei in ponds was proven feasible with the help of heated effluents. A significant negative relationship was found between damselfly nymph population density and final shrimp population density in ponds. Laboratory experiments confirmed and quantified this predator : prey relationship. Regression equations relating estimated shrimp population density based on cast net catches to actual population density based on cast net catches to actual population density were generated for future use as prediction equations. Distribution of both species was heterogeneous in ponds and unrelated to temperature, pH, dissolved oxygen, or pond bottom softness in this study. In polyculture ponds, P. vannamei apparently displaced P. stylirostris toward the shores