A STANDARDIZED COMPARISON OF SEMI-INTENSIVE POND CULTURE OF FRESH-WATER PRAWNS MACROBRACHIUM-ROSENBERGII AT DIFFERENT LATITUDES - PRODUCTION INCREASES ASSOCIATED WITH LOWER WATER TEMPERATURES

This study was conducted to evaluate the effects of different ambient water temperatures on growth and population structure of freshwater pr awns raised under standardized culture conditions, Juvenile prawns ave raging 0.26 +/- 0.14 g were stocked into seven 0.04 ha ponds at two st udy sites. Three ponds were located in Kentucky (KSU:latitude 38 degre es 12') with seasonal water temperatures averaging 24-26 degrees C. Fo ur ponds were located in Mississippi (MSU:latitude 33 degrees 28') wit h a seasonal average of approximately 30 degrees C, Prawn stocking, sa mpling, and harvest dates were identical at both locations. Juvenile p rawns were single source and were harvested from the same nursery tank for stocking at both locations. The diet used at both sites was from a single production run and was stored under refrigerated conditions. Prawns at both sites were fed twice daily according to a computer gene rated feeding schedule, Beginning approximately 8 weeks prior to harve st, sampled prawns were also individually identified according to sexu al morphotype, At harvest (117 days after stocking) all prawns at both sites were counted, morphotyped, and weighed, Prawn weights were high er at the more northerly site al all samples after 42 days post-stocki ng. When sampled 64 days post-stocking (5 August) no sexually mature m ale or females were found, Mature morphotypes were first captured in t he Day 83 sampling (25 August). In the Day 106 sampling (16 September) , there were no significant differences (P > 0.05) in numbers or weigh ts of the three male morphotypes between sites. However, among females there were significantly fewer (P less than or equal to 0.01) berried females at KSU with their average weights being significantly greater (P less than or equal to 0.05) than those at MSU (35 g and 31 g, resp ectively). At harvest(Day 117: 27 September) KSU had significantly (P less than or equal to 0.05) fewer berried females (32%) and more virgi ns (45%) than MSU (56% and 25%, respectively). Berried females at KSU weighed significantly more than at MSU (33 g and 26 g, respectively). There were no statistically significant differences (P > 0.05) between the two sites in prawn survival (83%), average weight (35 g), and fee d conversion (2.3). Production was significantly greater (P less than or equal to 0.01) at KSU (1261 kg ha(-1)) than MSU (1091 kg ha(-1)) la rgely reflecting higher average weights of some morphotypes and slight ly higher survivals. Differences in proportions and sizes of female mo rphotypes probably indicate delayed sexual maturation at the more nort herly site, prolonging somatic growth which normally ceases when food energies an redirected to reproductive activities.