Effects of Abrupt pH Increases on Survival of Different Ages of Young Channel Catfish and Hybrid Catfish

A previous study showed that fry of channel catfish Ictalurus punctatus are sensitive to pH increases but tolerant of pH decreases. This study determined the tolerance of channel catfish and hybrid catfish (female channel catfish × male blue catfish I. furcatus ) sac fry, swim‐up fry, and fingerlings to abrupt pH increases. Sac fry, swim‐up fry, and fingerlings of channel catfish and hybrid catfish are sensitive to abrupt pH increases and become more tolerant with age or size. Hybrid catfish sac fry were more tolerant than channel catfish sac fry at lower pH increases, as evidenced by their higher 24‐h LC10 (0.38 and 0.13 pH unit increases, respectively) and 24‐h LC50 (0.48 and 0.36 pH unit increases, respectively). However, the 24‐h LC90 for hybrid catfish sac fry (0.62 pH unit) was much lower than that for channel catfish (1.03 pH unit), showing that at higher pH increases hybrids are less tolerant. Channel catfish swim‐up fry were more tolerant of pH increases (24‐h LC50 = 1.28 pH units) than were hybrids (24‐h LC50 = 0.83 pH units), but hybrid catfish fingerlings (24‐h LC50 = 1.54 pH units) were more tolerant of pH increases than channel catfish fingerlings (24‐h LC50 = 1.33 pH units). When comparing fish acclimated to different starting pH levels, lethal concentration values increased correspondingly. This indicates that pH sensitivity is due to upper lethal pH limits rather than abrupt pH changes.