Abstract

A study was conducted to reveal how rice and red swamp crawfish (Procambarus clarkii) affect each other in the field and to determine the optimal stocking rates of crawfish. Nutritional composition of decayed rice stubble and other environmental parameters, i.e., soil nutrients and water quality were also determined. Eighteen earthen ponds were randomly assigned to six treatments in a two by three factorial arrangement: rice ponds and natural ponds, containing three different stocking rates of crawfish (0, 57, 114 kg of crawfish/ha), with three replications each. Natural ponds contained millet, smartweed, and sundry other natural vegetation. Rice production averaged 3,402 kg/ha and ranged from 2,519 kg/ha to 4,702 kg/ha. Different stocking rates of crawfish did not affect rice production. A high positive correlation was found between rice production and the number of adult crawfish that had lived in the rice field. Significant difference of average crawfish production was found between rice ponds (1059 kg/ha) and natural ponds (800 kg/ha). von Bertalanffy's growth model revealed that crawfish in rice ponds attained an average maximum length (L?) and a Brody's growth coefficient (K) of 123.2 mm and 0.153, respectively, whereas the crawfish in natural ponds had an L? and K of 106.9 mm and 0.184, respectively. Significant differences were observed for L? among treatments, but no significant differences were found for K among treatments. The inverse relationship between length of crawfish and the number of crawfish caught in all ponds was significant when the ponds reached carrying capacity. No significant differences of population were observed among six treatments and sampling dates. The highest initial C:N ratio of rice stubble was 107 before flooding. The rice stubble decomposed at an average water temperature of 10°C and under partially anaerobic conditions. It took 16 weeks for the C:N ratio to drop below 17. The result of soil analysis showed that organic matter in rice ponds and phosphate and potassium in both rice and natural ponds increased during the study. However, amounts of calcium decreased in both rice and natural ponds during the study. A significant inverse correlation was found between the increment of calcium and crawfish production. The oxygen content was consistently higher in natural ponds than in rice ponds at both dawn and dusk. The net daytime photosysthesis and nighttime respiration were usually higher in natural ponds than in rice ponds for 14 weeks after flooding, but they became lower thereafter.

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