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 its temperature requirements. Pacu introduction into the Israeli fish culture system is being considered. Temperature range in the region is 8-33 degrees C, thus the minimum winter water temperatures might be a limiting factor. To determine what is the minimum temperature pacu would tolerate, and hence which overwintering operations in warm-temperate regions are required for this warm water species, low temperature tolerance tests in the laboratory and observations in the field were carried out. Laboratory experiments reducing temperature by 1-3 degrees C per day were carried out with fish of 150-200 g, about the size pacu reach after one culture season. The field observations compared survival of two-year-old pacu of 1.3 kg mean weight overwintered in outdoors and in greenhouse ponds. For one-year-old fish 7.5 degrees C was found to be the lower temperature tolerance limit. Two-year-old fish withstand short exposures to this temperature rather well and their lower tolerance limit might be lower. This indicates that in warm-temperate regions pacu should survive in outdoors ponds. In this case some loss of weight should be expected, and suspension of feeding when temperature drops below 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 available water into the ponds is recommended if maximum water temperature drops to 10 degrees C or below. Overwintering in greenhouses or other heated facilities would be recommended if an exceptionally cold winter is expected and for regions with lower winter minimum temperatures.