Radiata2008(3)e

Herbert Meier & Ingo

Herbert Meier & Ingo Schaefer after the shell was first pierced. Hatchlings produced by Schaefer (1986) measured close to 5 cm in length; they weighed about 20 g, which would correspond to about 50 % of the total weight of the egg. On emerging, the nose of the hatchlings is still bent backward, and the skin flaps and barbels lie flush against the neck. The red colouration of the ventral side is intense. When the eggs of 2002 incubated by the senior author were checked for the last time on 07.01.2003, one showed two small holes in its shell. Within the next ten hours, the first little matamata left this egg. Another one cracked its eggshell during the early morning hours and stuck out its head and neck. It took only another hour for it to leave its egg completely. A third hatchling emerged on the same evening and left its egg within just twenty minutes. All three hatchlings had fully resorbed their yolk sacs, leaving only a small navel slit of about 5 mm long and 1 mm wide visible. These three eggs were part of the clutch laid on 20.07.2002 and had thus needed 172 days until they hatched. Between the 10. and 14. of January, another four babies emerged, having taken incubation periods of between 167 and 171 days. All hatchlings had fully resorbed their yolk reserves. The remaining two eggs were opened after 174 days of incubation on 17.01.2003. Candling had not shown any movement of the embryos inside. The first egg contained a fully developed, live baby turtle that had already resorbed its yolk sac. In contrast to its hatched siblings, however, it was positioned head-down in its egg. Head and neck were hidden beneath the body, and the left front leg was wrapped over the head. The neck of this specimen appeared curiously and unnaturally twisted. The remains of the egg fluid were dark brown and emanated a strong odour. Once the baby turtle had been freed from its egg, it tried to struggle free. What was peculiar was that it held its neck nearly at a right angle to the left. This kink in the neck would normalize a little over the following weeks, but in principle remain as it was. The last egg also contained a fully developed baby, which still had an external yolk reserve of some 5 mm in diameter. It left its egg spontaneously within just a few minutes on 24.01.2003, i.e., after an incubation period of 182 days. It was interesting to note that all of the seven baby turtles that had hatched on their own had opened their respective eggs in almost the very same spot, i.e., at an angle of about 45-50 °C to the horizontal axis, and all had been lying on their backs within their eggs. This lying on the back of the embryos had already been noticed during candling on 23.10., after which another ten weeks would go by. This observation contradicts Lehmann (1987), who concluded from the upside-down position that hatchlings would turn around right before or during the hatching process if they were unable to crack their eggshells otherwise. Raising The hatchlings begin to feed on small fish just a few days after leaving their eggs. Raising them is not a problem if a constant supply of small fish can be ensured. In nature, juveniles have a taste for tadpoles. With the keeper mustering some patience, they will learn to take dead, defrosted fish from forceps. The best time for feeding is during early dawn. Growth can be astounding under optimum husbandry conditions, and babies may have reached carapace lengths of 10-11 cm and weights of 120-150 g after only one year (Meier & Schaefer 2003a, b). Juveniles are not aggressive amongst each other. Adequate water quality needs to be ensured for which reason raising aquaria should be large enough. Like with the adult matamatas, the tank should be well-structured and offer several shelters. 34 RADIATA 17 (3), 2008

The Matamata, Chelus fimbriata All hatchlings obtained by Meier were transferred to an aquarium with a water level of 7-8 cm right after exiting their eggs. The water temperature was 26 °C while air temperatures ranged from 21 to far over 30 °C. Only a few days after hatching, the babies started feeding on small live fish such as guppies (Poecilia reticulata), black mollies (Poecilia sphenops) and cichlids (Tilapia sp.). Making them accept defrosted fish – smelt (Osmerus eperlanus) and topmouth gudgeon (Pseudorasbora parva) – proved very time-intensive and troublesome, however. It eventually took a few days of no other food to slowly make headway in this respect, but about two weeks after the last matamatas had hatched, all juveniles readily accepted defrosted smelt from forceps. Food was offered at least once every day, and it was irrelevant whether there was bright sunshine or the dimmed light of dawn or dusk. It took only two weeks for the baby turtles to come to the front of their aquarium at feeding time. Feeding then took just a few minutes for all nine of them. Gains in size and weight developed accordingly (comp. Meier & Schaefer 2003a, b). Fertilization and hatching rates The possible reasons for the as yet minor propagation rates can be categorized in two groups: for one, the causes of poor fertilization rates need to be analysed, and for the other part, the reasons for embryos perishing in their eggs, partly at a fully developed stage, need to be identified. There cannot be any doubt that the physical condition of the breeder specimens is of fundamental importance. Over the past years, husbandry conditions have been optimized to come ever closer to the biological requirements of the animals. The quality of their food is improved by supplementing it with vitamins. Whenever possible, they receive freshly caught live food. As a result of comparisons of weights between specimens in the terrarium and those in the wild, the rations per animal were reduced and adjusted to a seasonal rhythm. Both the amounts of food and intervals of feeding are closely linked to the behaviour of the turtles. As a useful indicator for feeding to be necessary has proven for Meier the company fish in the tank of the matamatas. If predation pressures on the fish increase, it is time to feed. The turtles have responded to this new regime with increased activity. The senior author also views water depth as an important factor. A water depth of at least the carapace length of the largest specimen makes mating much easier, if it is not a precondition for mating in the first place. Courtship entails the male to swim immediately or a little above the female for a few minutes. This component of the approach, or part of the stimulation process, is rendered impossible, or at least impeded, if the water level is too low. At a water level of less than 30 cm the weight of the male becomes an important factor during copulation. The size of the captive enclosure is likewise of major importance, but many Chelus fimbriata are housed in tanks that are way too small and have much too low water levels. The natural behavioural patterns of courtship and mating will therefore be impeded or made entirely impossible. It is a common observation that embryos perish at a fully developed stage (Drajeske 1983, Schaefer 1986, Rosscoe & Holmstrom 1996, Schaefer pers. comm.). Various authors have reported that eggs – individually and over a period of several days and even weeks – were dropped in the water (Heinroth 1943, Trutnau 1987, Rosscoe & Holmstrom 1996). The reason for this is clearly to be found in nesting facilities that are at best suboptimal. The resultant delay in oviposition is very likely to cause at least a partial overcalcification of the eggshells that may more or less obstruct the diffusion of RADIATA 17 (3), 2008 35