Abstract
During the two-month rearing period, the effect of four water temperatures (15°C, 20°C, 25°C and 30°C) on survival rate, number of molts, and growth rate (molt increment and intermolt period) of juvenile Macrobrachium borellii Nobili, 1896 and Palaemonetes argentinus Nobili, 1901 prawns was evaluated in laboratory conditions. The two species showed some similarities in their both survival and growth pattern at different temperatures. The survival rate was highest at 20°C and 25°C, decreasing at the lowest temperature. The number of molts increased at higher temperatures, ranging the intermolt period from 22.2 days to 9.9 days, for M. borellii, and from 20.8 to 9.5 days for P. argentinus, corresponding those values to 15°C and 30°C, respectively. No difference between species was noted in the intermolt period. The size increment by molting increased significantly from 15°C to 25°C, whereas a reduction in the growth of prawns was observed at 30°C. Significant differences among temperatures were found in the slope of regressions between the size increment by molting and the cephalothorax length. M. borellii showed a significantly higher tolerance to elevated temperature and a faster growth (about twice at 25°C) than P. argentinus. These differences could provide M. borellii a competitive advantage for a better adaptation to the dynamic of freshwater environment, especially in areas with anthropogenic impact.
Highlights
Several records show that water temperature fluctuates during the year between values higher than 30°C and lower than 10°C, following the climate pattern described for latitudes of 28°-32°S (Drago & Paira, 1987; Bonetto & Wais, 1995; Drago, 2007)
The influence of temperature on ectotherm organisms depends on the species distribution, range of thermal tolerance, and acclimatization occurring in response to the environmental fluctuations (SchmidtNielsen, 1997)
The species investigated in this study, Macrobrachium borellii and Palaemonetes argentinus, showed a high survival at 20°C (88 and 92%, respectively) and 25°C (96% for both species) suggesting that these temperatures are within the optimum temperature range for these prawns
Summary
Macrobrachium borellii Nobili, 1896 and Palaemonetes argentinus Nobili, 1901 are the most abundant palaemonids in the lagoons and streams of the Paraná River floodplain in South America (Boschi, 1981; Lopretto, 1995), having their entire life cycle in fresh water (Menu-Marque, 1973; Jalihal et al, 1993). In these environments, several factors such as seasonal changes in temperature and hydrometric level influence the biology and ecology of decapods fauna (Collins, 1999). The most efficient temperatures for their growth were identified for each species
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