In areas where this species has become depleted, fish populations have also shown a decline. They are also reputed to control piranha numbers. While it has been stated that little evidence is available to support this, C. yacare does demonstrate this particular dietary preference. In reality, it is likely that C. crocodilus is very much a generalist and adaptive predator, given its ecological success. Females become sexually mature at 1.2 m, which may be between 4 and 7 years depending on the population.
Social status affects growth rate and hence readiness for breeding.
Less dominant animals grow less quickly due to stress, and often do not get the chance to breed. Location is generally under cover, but some are sited in more open areas or on floating mats of vegetation. Nests may be shared by females, a strategy which may help to increase the survival of juveniles from each parent. Females will remain close to nests in an attempt to dissuade predators. When the juveniles hatch after around 90 days, there is usually a plentiful supply of invertebrate food available due to the timing of hatching.