Effect of hypoxia duration and pattern on channel Catfish (Ictalurus punctatus) neuropeptide gene expression and hematology

Commercial aquaculture production of channel catfish (Ictalurus punctatus) occurs in shallow ponds with daily cycling of dissolved oxygen concentration ranging from supersaturation to severe hypoxia. Once daily minimum dissolved oxygen concentration falls below 3.0 mg O-2/L, channel catfish have a reduced appetite, leading to reduced growth rates. In other fishes, upregulation of the neuropeptides corticotropin-releasing factor (CRF) and urotensin I (UI) have been implicated as initiating the mechanism responsible for decreasing appetite once an environmental stressor is detected. Channel catfish maintained at 27 degrees C in aquaria were subjected to varying durations and patterns of hypoxia (1.75 +/- 0.07 mg O-2/L) to evaluate underlying physiological responses to hypoxia and determine if hypothalamic CRF and UI are responsible for hypoxia-induced anorexia in channel catfish. During a short exposure to hypoxia (12 h), venous Po-2 was significantly lower within 6 h and was coupled with an increase of hematocrit and decrease of blood osmolality, yet all responses reversed within 12 h after returning to normoxia. When this pattern of hypoxia and normoxia was repeated cyclically for 5 days, these physiological responses repeated daily. Extended periods of hypoxia (5 days) resulted in similar hematological responses, which did not recover to baseline values during the hypoxia exposure. This study did not find a significant change in hypothalamic transcription of CRF and UI during hypoxia challenges but did identify multiple physiological adaptive responses that work together to reduce the severity of experimentally induced hypoxia in channel catfish.