Date of Award

1980

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forestry, Wildlife, and Fisheries

Abstract

Studies were conducted to determine the effects of flooding dates and different disposals of rice straw on crayfish culture in rice field. Nutritional composition of decayed rice straw, periphyton growth, and water quality were also determined. Eighteen earthen ponds were randomly assigned to six treatments in a two by three factorial arrangement: early flooding (20/Sept/1978), late flooding (15/Oct/78), and aerobic (baled), anaerobic (disked), partially aerobic (standing) decomposition of rice straw with three replications each. The average crayfish production in early-flooded ponds (1183 kg/ha) did not differ significantly from that in late-flooded ponds (1127 kg/ha). Significant differences (P < 0.05) in average crayfish production were found between standing ponds (1506 kg/ha) and disked ponds (803 kg/ha), and between baled ponds (1157 kg/ha) and disked ponds. The average crayfish production in standing ponds was not significantly higher than in baled ponds. von Bertalanffy's growth model revealed that all crayfish in early-flooded ponds attained an average maximum length (1(,00)) and Brody's growth coefficient (k) of 92.2 mm and 0.55, respectively, whereas all crayfish in late-flooded ponds had an 1(,00) and k of 82.7 mm and 0.09. Crayfish in disked ponds showed the poorest growth of all treatments. Late-flooded ponds had a higher population density than early flooded ponds. The population density was highest in baled ponds followed by standing and disked ponds. The harvestable crayfish size (total length > 75 mm) in decreasing order were: standing ponds (19.4 g), baled ponds (18.3 g), and disked ponds (17.0 g). Rice straw decomposed fastest in baled ponds, followed by standing ponds and disked ponds with average weight loss of 77.1, 66.6 and 48.9%, respectively, after 5-months decomposition. The C:N ratio or rice straw at flooding was 57. It took 4 months for the C:N ratio to drop below 17 for rice straw in baled and standing ponds. The average C:N ratio of rice straw in disked ponds was 23 after 5 months decomposition. The average dawn dissolved oxygen (DO) was consistently higher in early-flooded ponds than in late-flooded ponds with a difference of 1.3 mg/l. For the first 5-weeks after flooding, average dawn DO was highest in baled ponds (1.5 mg/l). After that, disked ponds had the highest dawn DO. Eighteen weeks after flooding, early-flooded ponds had higher periphyton biomass (337 g/m('2)) than late-flooded ponds (216 g/m('2)). The periphyton biomass was highest in standing ponds (358 g/m('2)), followed by baled ponds (333 g/m('2)) and disked ponds (307 g/m('2)).

Pages

132

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