Agonistic and thermal behaviour was studied in hatchling Crocodylus porosus under captive conditions using CCTV cameras. The results guided the design of experiments aimed at improving growth and survival of this species in captivity. C. porosus are born with a repertoire of 16 distinctive agonistic behaviours, and most interactions occur in the morning and evening in open, shallow water. There are clutch-specific differences in the frequency of agonistic interactions, and older hatchlings display fewer behaviours based on dominance status. A comparison of eight crocodilian species revealed differences in behaviours displayed and the level of conspecific tolerance, with C. porosus being the most aggressive. Hatchling C. porosus preferred body temperatures (Tbs) between 29.4ºC and 32.6ºC, and the mean (30.9±2.3ºC SD) was not influenced by social situation or feeding status. During the day, hatchlings had higher Tbs and were less active than at night. Growth of C. porosus during the first 24 days can be used to predict ‘failure to thrive’ (FTT) affliction up to 300 days. Hatchlings fed short chopped meat had higher growth than those fed standard mince or long chopped meat. Although visual barriers and deeper water reduced agonistic behaviour among hatchlings, these factors did not result in improved growth. Hatchling growth was highest at a density of 6.7/m2, and was lower at higher densities. The frequency of agonistic interactions was higher at lower densities (3.3/m2; 6.7/m2) than at higher densities (13.3/m2; 20.0/m2). Although hatchlings given Valium in their food had fewer agonistic interactions, they had reduced growth. Hatchlings raised under constant warm temperatures (32-34ºC), a gradient of temperatures, or warmer night time temperatures had higher growth than hatchlings with warm temperatures during the day only. Hatchlings afflicted with FTT and placed in a semi-natural enclosure had almost double the growth of those in standard raising pens.