Effects of Acute and Chronic Elevated pH Exposure on Survival of Hatchery Fry and Fingerlings of Select Sport Fish Species




Pence, Nathan E.

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Contrasting pH levels between indoor spawning raceways and outdoor production ponds are thought to be a factor contributing to low survival of fry and fingerlings at aquaculture facilities. Standard procedure is to move fiy and fingerlings from indoor hatching and holding facilities to outdoor grow out ponds. Often outdoor pH levels are higher than the indoor pH levels and fry and fingerlings are then subjected to those fluctuations in pH. Here I experimentally determined the effects of acute (instantaneous) and chronic (w/ acclimation time) pH changes on fry or fingerlings of the Florida largemouth bass Micropterus salmoides floridanus, smallmouth bass Micropterus dolomieu, channel catfish Ictalurus punctatus, and bluegill Lepomis macrochirus. To test for tolerances to acute pH levels I conducted single factor experiments with 5 pH treatments (9.0, 9.4, 9.7, 10.0, 10.5) and a control (incoming hatchery water supply w/ pH 8.1) and then used survivorship after 6 h as a response variable. ANOVA showed significant (p<0.05) mortality for all four species at varying pH levels: smallmouth bass 10.0, bluegill 10.0, Florida largemouth bass 9.7, and channel catfish 9.4. LC50 values were calculated using the Trimmed-Spearmen Karber method: smallmouth bass 10.22, bluegill 9.87, Florida largemouth bass 9.72, and channel catfish 9.39. Tolerances to pH changes were also evaluated by raising the pH from 8.1 to 10.1 over 5 time intervals (0, 15, 30, 45, and 60 min) and then determining survivorship after 2 h. ANOVA showed significant increase in survival only for the smallmouth bass, however smallmouth bass fry, channel catfish fry, and bluegill fingerlings (% increase in survival @ 60min acclimation time: 29.4, 19.2, 20) all three followed a general pattern of higher survivorship with increased time interval of acclimation to a chronic pH increase. Florida largemouth bass (10% increase in survival @ 60min acclimation time) fry exhibited only small increases in survival with increased time allowed for acclimation. These results suggest it is important for hatcheries to adopt culture methods that account for species-specific pH tolerances to maximize survival of fry and fingerlings.



fish hatcheries, hydrogen-ion concentration, fish culture


Pence, N. E. (2002). Effects of acute and chronic elevated pH exposure on survival of hatchery fry and fingerlings of select sport fish species (Unpublished thesis). Southwest Texas State University, San Marcos, Texas.


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