Genetic Response to Acute Hypoxia in Channel Catfish (Ictaluruspunctatus), Blue Catfish (Ictalurusfurcatus) and Hybrid Catfish
Type of Degreethesis
Fisheries and Allied Aquacultures
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The catfish industry is one of the largestdomestic aquaculture markets in the United States. In aggregate, the industry was valued at $423 million dollars in 2011 and is dominated by the production of channel catfish (Ictaluruspunctatus) and, to a lesser extant, hybrid catfish, a cross between channel female and blue male catfish (Ictalurusfurcatus). Dissolved oxygen (DO) levels are a critical component governing the success and profitability of catfish pond aquaculture. Low DO levels are known to negatively impact feed utilization/growth, health/stress levels, and ultimately survival. However, major gaps remain in our understanding of differential susceptibilities of channel, blue, and hybrid catfish to low DO and the molecular consequences of these events on critical genes governing metabolism/growth, stress/immunity, and overall physiological functions. Here, therefore, we examined both phenotypic and genotypic responses to acute hypoxia in the three catfish groups. It was determined that genotypic reaction to hypoxia is highly variable between the different catfish families, the various tissues and at between time intervals. Six different known catfish genes were investigated at time points of 2, 4, and 8 hr at 2mg/l dissolved oxygen and at 2 and 4 hr at 1.5mg/L in liver and gill tissue. The observed genes HIF-1, HIF-2, BPI, Ferritin, Myostatin and NKEF showed highly variable regulation changes at different time points and oxygen levels. Channel and hybrid catfish showed almost identical phenotypic stress response times while blue catfish were significantly quicker to show observable stress. This pattern of hybrid, channel similarity held true across the majority of treatments tested with this pairing showing much greater sensitivity to the HIF family of genes than their blue counterparts. Hybrid and channel catfish also showed similar genotypic response for BPI genes with multiple significant down regulated time points for BPI genes in gill and liver tissue. Both hybrid and channel catfish recorded their largest fold change of any gene at the 8 hr at 2mg/L time point in the ferritin liver trial reporting an up regulation of 26.9 fold and 75 fold respectively. The only tested gene that showed any similarity between blue and hybrid catfish was myostatin. Blue catfish showed a 24.1 fold up regulation in liver at 4 hr and 1.5mg/L oxygen level while hybrid catfish showed a 21 fold increase in liver tissue at 8 hr at 2mg/L oxygen. Outside of the myostatin gene blue catfish showed muted sensitivity to the treatments compared to channel and hybrid catfish. This study is one of the few investigating acute hypoxia as it relates to genetic change and so there are few other results to compare to. Our findings provide an early foundation of understanding of the consequences of low oxygen events and should provide a scientific basis upon which to set minimum DO thresholds for catfish aquaculture.