Evaluation of selection index for heat tolerance and growth traits and estimation of genetic parameters in selected populations of Procambarus clarkii

The red swamp crayfish (Procambarus clarkii) is an important cultured species in integrated rice-aquatic farming. In recent years, shallow-water temperatures in rice paddies have been elevated by climate warming. The development of heat-tolerant elite lines has therefore become an urgent need. To evaluate genetic parameters for heat tolerance and growth, and to clarify their genetic associations, upper thermal tolerance (UTT) and growth traits were measured in 18 paternal half-sib families (n=540). Using six microsatellite marker pairs, 498 individuals were successfully assigned to 51 full-sib families. High genetic diversity was indicated in the selected heat-tolerant, fast-growing line. The mean number of alleles (N_a) was 21.67. The mean observed heterozygosity (H_o ) was 0.52. The mean expected heterozygosity (H_e) was 0.74. The mean polymorphism information content (PIC) was 0.71. Based on a selection index, the top 20% families were identified. Compared with control families, body weight, body length, second abdominal segment width, and abdominal muscle weight were increased by 48.11%, 10.14%, 13.01%, and 16.05%, respectively (P<0.05). UTT was increased by 31.44% (P<0.01). Genetic parameters were estimated. The heritability of UTT was 0.64±0.07, indicating a highly heritable trait. Heritabilities of growth traits ranged from 0.29 to 0.53. Relatively high heritabilities were obtained for body length (h²=0.50±0.19), body weight (h²=0.49±0.19), and abdominal length (h²=0.49±0.19). A low heritability was obtained for the proportion of abdominal length (h²=0.07). Genetic correlations between UTT and growth traits were weak (0.06-0.50). Phenotypic correlations were also weak (−0.11-0.24). The results demonstrated that UTT and the major growth traits in P. clarkii are moderate-to-high heritability traits. No obvious negative genetic correlations were detected between UTT and major growth traits, indicating that simultaneous improvement of heat tolerance and growth performance can be achieved through independent or combined selection. In addition, the selected heat-tolerant and fast-growing strain maintained abundant genetic diversity and showed strong breeding potential. This study clarified the genetic characteristics and relationships between heat tolerance and growth traits in P. clarkii, and established a scientific evaluation approach for these traits. The findings provide important theoretical support and practical references for breeding heat-tolerant and fast-growing crayfish varieties, and contribute to the high-quality development of integrated rice-fish farming systems under increasing thermal stress.