Résumé
Temperature effects vary throughout the ontogeny, but are proportionally more variable during the early life stages than in older fish. The larvae of a few species have been studied but contrasting trajectories were observed, thereby making it difficult to predict how temperature impacts on the growth, survival and size heterogeneity in a particular species. This study examined these interactions in young [0.9 mg-1 g wet mass (WM)] Pangasianodon hypophthalmus, one of the most extensively cultured tropical fish. Fish were raised at five temperatures from 23 to 33 degrees C in a recirculated water system, fed in excess with a high-energy feed (Artemia then a formulated feed, > 50% protein), and examined at 1-day (first feeding days) or 4-day intervals (older fish). The temperature that produced the fastest growth (T degrees(opt)) was 31 degrees C at the start of exogenous feeding (0.9 mg); it increased to 32.7 degrees C at 8 mg then decreased by 0.7 degrees C for each 10-fold increase of WM. Size heterogeneity was lower and survival was higher (70-85% from 0.9 mg to 1 g) when the temperature was close to T degrees(opt). Comparisons with other species suggest that the slope of the relationship between T degrees(opt) and fish size has a strong latitudinal component, and may also reflect the fish sensitivity to oxygen.