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

Authors: MYERS, JAELEN - Auburn University; DYCE, PAUL - Auburn University; Chatakondi, Nagaraj; GORMAN, SARA - Auburn University; Quiniou, Sylvie; SU, BAOFENG - Auburn University; PEATMAN, ERIC - Auburn University; DUNHAM, REX - Auburn University; BUTTS, IAN - Auburn University

Submitted to: Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2020
Publication Date: 2/17/2020
Citation: Myers, J., Dyce, P., Chatakondi, N.G., Gorman, S., Quiniou, S., Su, B., Peatman, E., Dunham, R., Butts, I. 2020. Analysis of specific mRNA gene expression profiles as markers of egg and embryo quality for hybrid catfish aquacultures. Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology. 243:110675.

Interpretive Summary: Hybrid catfish are increasingly raised in US farm-raised catfish industry. Hybrid catfish fry are reliably produced by fertilizing strip spawned channel catfish eggs with blue catfish fry in hatcheries. Egg quality of strip-spawned channel catfish varies due to differences in maturation, hormone, nutrition, environmental variables and handling stress. No practical measures to determine egg quality exist, hence the present study aims to develop molecular markers to screen poor quality eggs in hatchery to consistently and increased hybrid catfish fry production in hatcheries. High and low quality of strip-spawned channel catfish eggs were determined based on neurulation and hatching success of 30 fish in a spawning trial. Developing embryos were sampled at 0, 24, 48 and 96 hours post fertilization. Gene expression of low quality and high-quality eggs and the abundance of these mRNA transcripts is linked to critical cellular function to link hatching success and embryo viability and survival of hybrid catfish. MicroRNA linked to egg quality and embryo viability were determined in hormone-injected Channel Catfish female fish under hatchery conditions. Maternally derived mRNA for select genes were expressed at four stages of embryonic development for high- and low-quality stripped eggs. Hence, by linking these markers to physical indicators of egg quality that can predict neurulation and hatching success. The findings of this study provide tools to screen high- and low-quality eggs in hybrid catfish hatcheries for reliable and increased production of hybrid catfish fry in hatcheries.

Technical Abstract: High variability in egg quality of fish exists due to many factors and can be challenging to assess. In a few fish species, egg quality and generation of viable embryos is correlated to abundances of specific mRNAs. Channel catfish (Ictalurus punctatus) females show considerable extremes in egg quality, causing inconsistencies in Channel catfish 'X Blue catfish (I.furcatus) ' hybrid fry production. The objectives of this study were to examine mRNAs linked to egg and embryo quality and determine expression between low-hatch and high-hatch eggs batches through development (0, 24, 48, and 96 hours post-fertilization; HPF). RNA was extracted from eggs/embryos of nine females (n = 4 high quality, n = 5 low quality) and real-time q-pCR was used to quantify relative gene expression. The transcripts assessed in this study perform critical cellular functions, including Tubulin ß (tubb), Cathepsin D (ctsd), Cathepsin Z (ctsz), Cathepsin B (ctsb), Cyclin B (ccnb1), Exportin-1 (xpo1), Ring finger protein 213 (rnf123), glucocorticoid receptor-1 (GR-1), and heat shock protein 70 (hsp70). Relative gene expression of all transcripts except GR-1 and hsp70 was 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 of embryo development, maternally-derived mRNAs for these genes do not seem to impact early embryonic development. Developing these molecular markers linked with physical indicators of egg quality, it is possible to eliminate poor quality eggs to enhance hybrid catfish fry production in hatcheries.