ARS | Publication request: Effects of abrupt pH increases on survival of different stages of young channel catfish and hybrid catfish

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 22, 2011
Publication Date: April 2, 2012
Citation: Mischke, C.C., Chatakondi, N.G. 2012. Effects of abrupt pH increases on survival of different stages of young channel catfish and hybrid catfish. North American Journal of Aquaculture. 74:160-163.

Interpretive Summary: Catfish farmers routinely stock hatched fry in nursery ponds and also move fingerlings from pond to pond within or between farms. Abrupt change in environmental conditions may be a possible explanation for poor and variable survival of stocked hatchery fry. Methods to moderate temperature differences in hauling water and nursery pond are currently adopted; however, there are no practical methods to acclimate pH of hauling water during transportation of fry from hatchery to stocking ponds. We evaluated the relative tolerance of channel catfish and hybrid catfish sac fry, swim-up fry and small fingerlings to the abrupt increases in pH of stocking waters in ponds. The results indicate that channel catfish and hybrid catfish fry were sensitive to abrupt pH increases and fish became more tolerant of pH increase with age/size. Hybrid sac fry were more tolerant than channel catfish sac fry at the lower pH increases as evidenced by their higher LC10 and LC50 values. The associated mortalities of catfish may be due to the pH of stocking water may have reached its upper limits rather than the toxicity due solely to abrupt pH changes in the study. These findings suggest catfish farmers to routinely monitor pH in nursery ponds prior to stocking fry from the hatchery. The study also advocates that fry and fingerlings be moved to equal or lower pH waters and inhibit stocking activity in ponds that attain pH levels close to 9.8 and above.

Technical Abstract: A previous study showed channel catfish Ictalurus punctatus fry are sensitive to pH increases, but tolerant to pH decreases. This study determined tolerance of channel catfish and hybrid catfish sac fry, swim-up fry, and fingerlings to abrupt pH increases. Sac fry, swim-up fry, and fingerlings of catfish and hybrids are sensitive to abrupt pH increases and become more tolerant with age/size. Hybrid sac fry were more tolerant than catfish sac fry at lower pH increases as evidenced by their higher LC10 (0.38 and 0.13 pH unit increases, respectively) and LC50 (0.48 vs. 0.36 pH unit increases, respectively). However, LC90 for hybrid sac fry (0.62 pH unit) was much lower than that for catfish (1.03 pH unit), showing that at higher pH increases, hybrids are less tolerant. Catfish swim-up fry were more tolerant of pH increases (LC50 = 1.28 pH units) than were hybrids (LC50 = 0.83 pH units), but hybrid fingerlings (LC50 = 1.54 pH units) were more tolerant of pH increases than catfish fingerlings (LC50 = 1.33 pH units). When comparing fish acclimated to different starting pH, LC values increased correspondingly. This indicates previous sensitivity may be due to upper lethal pH limits rather than abrupt pH changes.