Growth rate and plasma corticosterone levels in juvenile alligators maintained at different stocking densities

Abstract

Sixty-six captive-reared, juvenile alligators maintained in environmentally controlled chambers were randomly assigned to four treatments consisting of stocking densities of 0.35, 0.18, 0.12, and 0.09 m'/alligator. Alligators were maintained at these densities for 3.5 months. At approximately 4 week intervals the alligators were weighed, measured, and bled via cardiac puncture. Duplicate aliquots of plasma were assayed for corticosterone. All of the alligators continued to grow during the experiment, but alligators maintained a t the lowest stocking density were significantly heavier and grew significantly faster (P < 0.01) and had significantly lower plasma corticosterone (P < 0.01) than alligators maintained a t the highest stocking density. These results indicate that crowding (i.e., high-density rearing) of juvenile alligators inhibits maximum growth and that the subsequent stress associated with this crowding results in chronically elevated plasma corticosterone. Plasma corticosterone showed a strong negative correlation with change in body weight; the faster the rate of growth, the lower the hormone levels. These results also show that a single blood sample taken at monthly intervals is sufficient to monitor chronically elevated plasma corticosterone in this species.

Non-invasive assessment of adrenocortical function in captive Nile crocodiles (Crocodylus niloticus)

“…In captivity, very low stocking rates are usually not the norm due to the cost of space, while high stocking densities are avoided to reduce fighting and therefore injuries (Huchzermeyer, 2003). Crowding of juvenile crocodilians also inhibits maximum growth and this behaviour is associated with chronically elevated plasma corticosterone levels (Elsey et al, 1990). From an endocrinological perspective, a recent study on Saltwater crocodiles (Crocodylus porosus) by Isberg and Shilton (2013) shows no difference in plasma corticosterone concentrations between individually and communally housed animals.…”

Developmental abnormalities of the gonad and abnormal sex hormone concentrations in juvenile alligators from contaminated and control lakes in Florida.

“…cursor cholesterol, 4) modification of the enzymes required for steroidogenesis (e.g., aromatase, cytochrome P450SCd, and 5) modifications of the cellular receptor numbers and function (51). Peterson et al (20) reported a decrease in plasma testosterone concentration in rats exposed in utero to small concentrations (0.064 mg/kg) of dioxin.…”

“…The reproductive development of alligators from a contaminated and a control Lake in (2)(3)(4)(5). The American alligator (Alligator mississippiensis) was listed as an endangered species in the early 1970s, but populations throughout the southeastern United States grew rapidly after federal protection was instituted (6)(7)(8).…”

“…However, this mean misrepresents actual viability of many clutches from Lake Apopka, as we observed that these clutches either produced many offspring or no offspring. Of the 24 clutches of eggs incubated, 8 clutches produced no viable offspring, whereas 5 clutches exhibited viability rates of 75% or greater. Neonatal survival was reduced for young from Lake Apopka with 41% mortality within 10 days after hatching, whereas mortality for neonates from Lake Woodruff was less than 1%.…”

Turning crocodilian hearts into bird hearts: growth rates are similar for alligators with and without right-to-left cardiac shunt

“…Alligators from either sham or experimental treatments (see below) were randomly distributed amongst tanks. In order to avoid density-dependent growth effects (Elsey et al, 1990), density was progressively decreased from hatching (~16 alligatorsm -2 ) until they were sacrificed (~4 alligatorsm -2 ), as alligators grew. In addition, animals were housed in tanks based on body mass (e.g.…”