Radiata2008(3)e

Herbert Meier & Ingo

Herbert Meier & Ingo Schaefer provided to the breeder specimens, could possibly be found in alternative incubation methods. As has been mentioned before, oviposition takes place in nature right on the bank of a water body after the peak of high water. At this point of time, the substrate is likely to be still very moist. As the dry season then progresses, the soil will become substantially drier. Rains now sometimes fall only at three-day intervals. The time of hatching then coincides with the beginning of the next rainy season, and although water levels may still be rather low, the soil that serves as an incubation substrate becomes moister once more. Based on these observations, Meier began to experiment with controlled alterations to the moisture content of the incubation substrate for eggs of Macrochelodina rugosa and was, after several years of failures, eventually successful (Meier 2004). A slightly acidic substrate – as is used by McCord – could help improve the breathing capabilities of the egg by gradually dissolving the calcium of the eggshell. Various types of incubators have been tried out for matamata eggs and produced various results. Meier found the Jäger Kunstglucke entirely unsuited. Owing to its construction, the upper sides of the large eggs are very close to the heating element, which causes them to dry out substantially and possibly even to overheat while the lower parts of the eggs remain moist and cool. On the other hand, Zwartepoorte (pers. comm.) has been using this incubator successfully in conjunction with vermiculite. The senior author also failed with an incubator according to Budde (1980): either the degree of relative humidity dropped below Fig. 15. A two year-old juvenile of about 16 cm in carapace length. acceptable levels, or the eggs drowned in the wet substrate at 100 % relative humidity. Best results were so far obtained by means of a self-made incubator in the shape of a simple styrofoam box. Besides the container with the substrate, it holds a small water container. It is heated with a thermostat-controlled aquarium heating rod. Humidity levels are controlled by adjusting the cover of the water container. The exchange of air is facilitated by a few holes of 1-2 mm in diameter drilled into the box. An incubator in the shape of a modified bar fridge also allows for perfect control. Working on the same functional principles as the styrofoam box, its glass door even offers a distinct advantage: Without having to open the door, incubating eggs can at least be checked visually. The eggs obtained by the senior author in 2002 were embedded in moist moss and placed in the mentioned Jäger incubator. Relative humidity inside the incubator ranged around 72 % at a temperature of just under 30 °C. The eggs were not fully covered with the substrate. In eight of these eggs, a whitish spot developed on the upper side already on day two after oviposition. The second clutch from 2002 was transferred to an incubator modified from Budde (1980) and exposed to 32 RADIATA 17 (3), 2008

The Matamata, Chelus fimbriata an incubation temperature of 29-30 °C (Meier & Schaefer 2003a, b). Altogether thirteen eggs had turned snow white after about three weeks, while the remaining eight subsequently began to stink over the next months and had to be removed. On 25.09., the eggs were candled for the first time. Those that were fertile were notable for their being distinctly darker and containing blood vessels. Even though eight of the nine eggs in the Jäger incubator were apparently fertile, only three showed a similar development along the same timeline. Although two more contained blood vessels, their darkening was hardly perceivable. The by far best results came from the styrofoam incubator, though. Six of the original twelve eggs developed clearly distinguishable blood vessels and dark, opaque patches while another one showed blood vessels, but merely a faint dark spot. The reasons for these differences are probably to be found in the eggs being covered with moist substrate all around, and thus kept moist all around in an environment with more than 90 % of relative humidity in the styrofoam incubator as opposed to just 72 % in the Jäger incubator. By 29.09., the total number of incubating eggs had shrunk to thirteen. All eggs were now transferred to the styrofoam incubator where incubation temperatures were still maintained at 29-30 °C. The eggs were candled once more on 23.10., which revealed they had developed further. The blood vessels were more distinct now, the embryos had clearly grown over the past four weeks, and some were moving vigorously. From this point of time to around Christmas, checks were limited to visual inspections, and temperature and humidity levels were closely monitored. On 15.12.2002, the incubation temperature was raised to 30-31 °C. The substrate, which over the last weeks had only been moderately moist to almost dry, was remoistened, causing the level of relative humidity to rise to nearly 100 %. The eggs showed distinctly moist patches on their surfaces. Three eggs, which had turned grey and started stinking within a day, were opened. All had been fertile, but their embryos had obviously perished some time ago and were only a few millimetres in length. Now the coloration of the remaining nine eggs changed from snow white to a dirty, yellowish white. Around New Year, 160 days after oviposition, dark grey spots appeared, covering from just 1 mm² to about 1 cm² of the surface. An air bubble was clearly visible in four of the eggs. They were candled once more on 26.12.2002 and, like on 23.10. before, embryonic turtles could be seen moving inside. The weights of the eggs had increased by 2-4 g from an initial 36 to 38-40 g (taken with a digital scale with ± 2 g accuracy). Fig. 16. A six or seven year-old specimen of close to 30 cm in dorsal shell length. Hatching Hausmann (1964) reported that hatching would occur within a few minutes RADIATA 17 (3), 2008 33