Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Renewable Natural Resources

First Advisor

William R. Wolters


Potential for genetic improvement of red swamp crawfish, Procambarus clarkii, and the possibility of negative selection for growth in cultured stocks as a result of harvesting practices have recently been the subject of speculation. This study provided indications of the potential for improvement of growth and processing traits in P. clarkii through selection. After 150 days growout in fiberglass pools planted with rice (Oryza sativa), P. clarkii from each of 39 full-sib families nested within 15 half-sib families were weighed and measured for total length, carapace length, carapace width, abdomen width, abdomen depth, chela length, chela width, abdomen meat weight, and dressout percentage. Total length and weight were adjusted for density at harvest; other traits were adjusted for total length. Heritabilities of traits were estimated from a nested analysis of variance for all animals combined and for reproductively mature (Form I) males, immature (Form II and juvenile) males, and females separately. Genetic and environmental correlations and heritabilities of traits were estimated for all animals combined using mixed model analysis, with sex and male maturity as fixed effects. Broodstock were selected from full-sib families for family selection and 5 replicates of mass selection for growth in length. Three replicates of mass selection and one replicate each of one-way positive and negative family selection produced sufficient offspring to determine responses. Offspring were stocked for growout into replicate pools. Differences between lines in total length, weight and dressout percentage were analyzed within each replicate. Sire heritability estimates for growth and body size traits for all animals combined were not significant (P $>$ 0.05); estimates from mixed model analysis agreed with those from the nested analysis. Genetic correlations between growth in length and processing traits were positive and highly significant (P $<$ 0.01). In spite of moderate to high selection intensities (0.74 to 4.57), no response for growth in total length was observed. Similarly, no trend of correlated response in dressout percentage could be discerned. Results suggest P. clarkii exhibits little additive variation in growth traits, although genetic gains in dressout percentage may be possible.