THE EFFECTS OF ENVIRONMENTAL AND HANDLING STRESS ON THE PHYSIOLOGY AND MEAT QUALITY OF CHANNEL CATFISH

Stress during fish culture can impact growth, physiology and fillet quality.  Maintenance of high quality seafood is important to ensure the production of a highly marketable product.  The present study assessed catfish (Ictalurus punctatus) physiological responses to sequential stressors and their effects on fillet quality.  Temperature (i.e., 25°C or 33°C) and dissolved oxygen (DO, i.e., ~2mg/L or >5mg/L) were maintained for four weeks, followed by confinement and handling stressors (i.e., socking and transport) for a total of 12 treatments.  After each stage of harvest (environmental stress, socking and transport), physical (length, weight and feed consumption), physiological (hematocrit, plasma cortisol, pH, glucose, lactate, total protein, osmolality and ionic composition) and fillet quality (color and sensory) attributes of the fish and fillets were evaluated.  Fillet yield decreased with increasing severity of environmental stress.  Overall, increasing stress resulted in decreased feed consumption, growth and fillet yields.  A cumulative stress response was identified based on circulating cortisol and glucose, which increased with each sequential stress event. Under low oxygen conditions there was a suppression of the stress response. Handling imposed a more pronounced physiological response than environmental conditions.  Increased redness was found in fish reared under high temperatures and oxygen levels, suggesting an increased prevalence of red fillets can be expected.  Sensory analysis revealed that flavor acceptability increased with increasing stress due to less earthy and off-flavor accumulation, presumably due to decreased feed consumption and protein accretion.  These data highlight the importance of monitoring pre-harvest environmental conditions over time as a means of predicting how fish will respond physiologically to a harvest event, which may also impact survival and post-harvest quality.