Genotype by environment interactions for inner shell color and growth traits in the purple freshwater pearl mussel, Hyriopsis cumingii, reared with different water depths and mud substrates

A breeding selection program for improving inner shell color and growth was developed for Hyriopsis cumingii, to enhance purple pearl production. In freshwater pearl culture, adjusting culture water depth and mud substrate supply are routinely carried out to improve pearl quality. To improve selection decisions in different conditions, we estimated heritabilities and genotype by environment (G × E) interactions on inner shell color and growth traits in 1571 17-month-old animals from 8 half sib family of purple selective strain of H. cumingii reared in different water depths (WD₁, 32 cm; WD₂, 48 cm) and mud substrates (MS, mussel pond mud substrate; SS, shrimp pond mud substrate) were analyzed. With the same mud substrate, H. cumingii reared at WD₁ showed increased performance in shell color and growth. Heritability estimates for growth traits (shell length, shell height, shell width, body weight and shell weight) were higher at WD₁ and higher at WD₂ for inner shell color parameters (L, a, band dE⁎) when rearing in MS, while showed opposite pattern in SS. At the same water depth, H. cumingii reared with MS showed better performance in shell color and growth traits. Heritability estimates for growth traits were higher in SS and higher in MS for inner shell color parameters when rearing at WD₁, while showed opposite pattern at WD₂. Heritability estimates for L, a and all growth traits were moderate and high (h² > 0.15), while were low for b and dE⁎ (h² < 0.15). Genetic correlations for inner shell color parameters and growth traits within the four conditions were less than 0.8, except that some combinations of depth and mud substrate with over 0.9 for shell growth traits and shell color traits showed significant G × E correlations. The rank of individuals with comprehensive breeding value was different in four conditions, and the percentage of individual family sources shared in some pair conditions were small, which indicated re-ranking during selective breeding program. This study provides guidelines for a selective breeding strategy for improving inner shell color and growth in H. cumingii when mussels are reared under different conditions