Herbert Meier & Ingo Schaefer lowing an exchange of their water, each turtle consumed several fish every day. After about five days, i.e., shortly before another water exchange was due, all juvenile matamatas ceased feeding. Food was then once more accepted right after their water had been replaced. If the renewal of their water was limited to a partial exchange, they refused to feed already on day three or, at the latest, day four. A low pH-value has positive effects on juveniles. Whether these are a direct result of the increased degree of acidity of the water or a function of increased concentrations of ammonium, ammoniac, or nitrates has not been investigated, though. During the course of the senior author’s last journey to the Casiquiare River in February of 2006, his travel companion, Jan Michels, recorded conductivity values of 5-12 µS/cm at a temperature of 27 ± 0.5 °C, as well as pH-values of 4.9-6.63. Feeding Matamatas feed in a very particular manner and it is therefore that their feeding behaviour has been described many times before. Prey animals are sucked in at great speed by suddenly opening the huge mouth and expanding the neck. Once the food item is in the throat or at least between the jaws, the latter are closed to a narrow slit and the sucked-in water is pressed out. A detailed account of food acquisition and ingestion of prey was given by Lemell et al. (2002). The imbibing and expulsion of water were particularly clear to see in the case of a school of baby fish. A turtle identified a “cloud” of some 100-150 juvenile fish of Fig. 4. The original trickle filter could not cope with the pollution caused by the river turtles, Podocnemis spp., which were kept in the same tank... about 6 mm in length as food and captured many of them with the described suction technique. When the water that had been sucked in together with them was subsequently expelled through the gap between upper and lower jaws, the tiny fish were also flushed back into the aquarium. Chelus fimbriata is first and foremost piscivorous in its feeding habits. Mice or one-day chicks are accepted only on rare occasions. The turtles are therefore to be fed with all types of fish available (e.g., goldfish, carp, tench, orfe, river bass, trout, etc.), but never with diseased ornamental fish or other risk-bearing items. Fish are offered alive whenever possible, but more often than not, only deepfrozen fish are available; these have to be thoroughly defrosted before use. As a general rule, fish should be given whole and not gutted. Every dead fish is fortified with a bear yeast tablet, and their nutritional content 24 RADIATA 17 (3), 2008
The Matamata, Chelus fimbriata is further raised with a vitamin supplement (StressVitamN 0.03 mg/kg body mass) every two to three weeks. Every matamata receives 100-300 g of fish on average per week, depending, amongst others, on the season. According to information obtained from native Indians, the stomachs of matamatas only ever contain fish, but a black sludge also present suggests that tadpoles are consumed as well (Meier & Schaefer 2003a, b). In fact, tadpoles are readily accepted as food, and it would appear that these are targeted specifically from amidst fish. After a turtle has fed, it reduces all its activities. Comparison of free-ranging and captivekept juveniles of Chelus fimbriata of about the same age revealed clear differences. Specimens with approximately the same carapace lengths kept in human care weighed more by 50 to 70 %, in one instance even as much as 170 %, than those found in the wild. It has to be presumed that these ratios also apply to adult animals. Constant overfeeding with Fig. 5. ...and was therefore replaced with a new linear filter with a volume of 1,200 litres. possibly low-quality food is likely to be an important reason for a lack of reproductive activity in captivity. Social interaction and behaviour in captivity As has been mentioned above, matamatas present themselves as surprisingly agile when kept in tanks of appropriate dimensions. They walk and swim about a lot from the time of late dawn until the late morning hours. Another period of activity begins in the early evening hours and ends when it has become completely dark (depending on when the lights in the greenhouse are finally switched off). During the winter months, the lights usually remain on until at least 22.00 h every day. Intensity of all activities is reverse proportional to the feeding regime: the more food the turtles receive, the less active they will be. The animals encounter each other often during their walking and swimming about. Males will then often face off side by side in a display of a bent and vertically tilted neck. The carapace will also be tilted upwards in order to increase the perceived body size. Every now and then, these encounters may lead to minor biting fights, during which the competitors specifically target the rear parts of their opponents (tail, thighs). The inferior specimen will soon leave the “arena”, and no injuries resulting from these skirmishes have ever been noted. This behaviour is more rarely seen if there are no females present in the same tank. Females are courted again and again. Schaefer (1986) described this behaviour as follows: The otherwise typical daily period of rest was disturbed by an eager male walking and swimming RADIATA 17 (3), 2008 25
