Abstract
Cold resistance of blue tilapia (Tilapia aurea) was measured as the first step in development of a simulation model to predict acclimation state and mortality of tilapia exposed to varying low temperature. The model is based on F.E.J. Fry's "lethal dose" concept: Total lethal dose is the sum of accumulated incremental doses defined by the ratio Lt/tr, where &t andtrare, respectively, exposure time and expected resistance time at a given lethal temperature. Fifty percent mortality is predicted if and when total dose equals one. Cold-resistance times were determined for tilapia acclimated to 16, 20 or 240C and exposed to lethally low temperatures ranging from 6 to 12'C. The data then were used to parameterize a linear regression equation describing resistance time as a function of ambient and acclimation temperatures. In the next stage of the study, acclimation rate was determined for blue tilapia transferred between 160C and 24'C and between 240C and 320C. Resistance time at criterion temperatures of 60C and 1 O'C was used to measure the progress of acclimation. These data were incorporated in a predictive equation for acclimation temperature. Resistance time was calculated from the regression equation and was used to predict accumulated lethal dose. The model gave accurate predictions for step-changes in temperature below the -LILT (lower incipient lethal temperature) and reasonable predictions when cooling started above LILT. However, the model consistently underestimated resistance time when temperature fluctuated above and below LILT. The addition of a component to allow recovery from cold damage could improve model predictions. At this time, no data exist on which to base such a component. Muscle lipids of blue tilapia also were measured at three acclimation temperatures and during changes in acclimation to determine if this subtropical species displays the same thermal characteristics as temperate species. The ratio of phosphatidylcholine to phosphatidylethanolamine (PC:PE) was lower at low acclimation temperatures, which is consistent with observations on temperate species. PC:PE ratio during thermal acclimation was variable, and no clear pattern was observed. Blue tilapia also displayed, in muscle polar lipids, the ability to reduce saturated fatty acids and increase polyunsaturated fatty acids, especially 22:5n-3, at low temperatures, also consistent with temperate species.
Bruckler, Rita Marie (1995). Cold tolerance and thermal acclimation of juvenile blue tilapia, Tilapia aurea. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1561407.