Analysis of specific mRNA gene expression profiles as markers of egg and embryo quality for hybrid catfish aquaculture

Despite best efforts to optimize reproduction, egg incubation, and larval performance in captivity, inconsistencies in hatchery fish production are still created by high variations in egg quality from individual females. In some hatchery species, egg quality and generation of viable embryos are correlated to abundances of specific mRNAs. Channel catfish females show considerable extremes in egg quality, causing inconsistencies in channel catfish, Ictalurus punctatus, female x blue catfish, Ictalurus furcatus, male hybrid fry production. The objectives of this study were to examine relative transcripts linked to egg and embryo quality and determine expression between low-hatch and high-hatch egg batches through early development (0, 24, 48, and 96 h post-fertilization; HPF). RNA was extracted from eggs/embryos of nine females (n = 4 high-quality, n = 5 low-quality) and Real-Time PCR was used to quantify relative gene expression. The transcripts assessed in this study perform critical cellular functions, including tubulin beta (tubb), cathepsin D (ctsd), cathepsin Z (ctsz), cathepsin B (ctsb), cyclin B (ccnb1), exportin-1 (xpo1), ring finger protein 213 (rnf213), glucocorticoid receptor-1 (GR-1), and heat shock protein 70 (hsp70). Relative gene expression of all transcripts except GR-1 and hsp70 were up-regulated in the high-hatch group and peaked at 48 HPF (neurulation stage), indicating the importance of these gene products at this threshold to normally progress until hatch. Due to lack of expression during earlier stages, maternally derived mRNAs for these genes do not seem to impact early embryonic development. Using mRNA markers as a selection mechanism for hatchery broodstock may lead to more high-hatch egg batches by reducing problems associated with poor egg quality.