Low temperature tolerance of pacu, Piaractus mesopotamicus

Pacu, Piaractus mesopotamicus (=Colossoma mitrei), is a South American warm water fish species found in the temperature range of 15-35 degrees C. The culture of a warm water species in temperate regions demands knowledge on i ts temperature requirements. Pacu introduction into the Israeli fish cultur e system is being considered. Temperature range in the region is 8-33 degre es C, thus the minimum winter water temperatures might be a limiting factor . To determine what is the minimum temperature pacu would tolerate, and hen ce which overwintering operations in warm-temperate regions are required fo r this warm water species, low temperature tolerance tests in the laborator y and observations in the field were carried out. Laboratory experiments re ducing temperature by 1-3 degrees C per day were carried out with fish of 1 50-200 g, about the size pacu reach after one culture season. The field obs ervations compared survival of two-year-old pacu of 1.3 kg mean weight over wintered in outdoors and in greenhouse ponds. For one-year-old fish 7.5 deg rees C was found to be the lower temperature tolerance limit. Two-year-old fish withstand short exposures to this temperature rather well and their lo wer tolerance limit might be lower. This indicates that in warm-temperate r egions pacu should survive in outdoors ponds. In this case some loss of wei ght should be expected, and suspension of feeding when temperature drops be low 16-18 degrees C is recommended to avoid wasting feed that the fish will not consume anyway. To be in the safe side, inflow of the warmest availabl e water into the ponds is recommended if maximum water temperature drops to 10 degrees C or below. Overwintering in greenhouses or other heated facili ties would be recommended if an exceptionally cold winter is expected and f or regions with lower winter minimum temperatures.