Combined effect of temperature, salinity and dissolved oxygen on the survival of Nile tilapia (Oreochromis niloticus) fry during transportation, at different densities and durations

The transport of live fish is a delicate aquaculture operation that is carried out to distribute the fry or juveniles produced in the laboratories, to the culture farms. In the present work, survival after transport, survival during the subsequent 8 days (8-D PTS), and blood glucose as an indicator of stress, were determined in a simulated transport of Oreochromis niloticus tilapia fry of two sizes (1.2 +/- 0.3 g and 2.4 +/- 0.3 g), to find the best transport conditions. A total of 63 treatments per size, were tested combining three transport times (4, 8, and 24 h), three densities (54, 66, and 80 g/L), three temperatures (20, 22, and 24 degrees C), three salinities (3, 6, and 9 parts per thousand) and three concentrations of dissolved oxygen (DO) (10, 15, and 20 mg/L). The tests were carried out in 2 L plastic bags, containing 0.5 L of water and an atmosphere above of pure oxygen. In general terms, the tested conditions of temperature, salinity, DO and density did not produce fry mortality at the end of transport in any of the treatments. However, the 8-D PTS gradually declined during the first 4-5 days and stabilized up to day 8 of experimentation. Survival of small fry of 1.2 +/- 0.3 g was significantly (P < 0.05) lower (77.7 +/- 10.4%) compared to that (94.2 +/- 6.1%) obtained in 2.4 +/- 0.3 g fry. The expected 8-D PTS was plotted as response surfaces to show 8-D survival as a function of density, transport time, and fry weight. Mortality during the 8-day post-transport period was the result of the combined effect of temperature and handling of the fry, rather than due to a lack of oxygen or ammonia concentrations since both variables were at tolerable levels for the species. With these results, it is concluded that the best transport conditions, under the evaluated scenarios, are obtained with fry of 2.4 +/- 0.3 g transported at a density of 80 g/L for up to 24 h, at 24 degrees C and 3 parts per thousand.