THE EARLY ONTOGENY OF THE SOUTHERN MOUTHBROODER, PSEUDOCRENILABRUS PHILANDER (PISCES, CICHLIDAE)

The early development of the southern mouthbrooder, Pseudocrenilabrus philander, is documented from activation until the early stages of the juvenile period. The duration of the embryonic period is about 14 day s at 25 degrees C. Development is direct and there is accelerated exog enous feeding into the embryonic period. The pattern of development an d the timing of ontogenetic events and structure formation are a refle ction of both internal and external environmental conditions. During m outhbrooding, oxygen uptake is facilitated by embryonic respiratory pl exuses and flapping of the pectoral fins. At the time of first release from the buccal cavity, the embryos are in an advanced state of devel opment. The switch-over from the temporary embryonic respiratory syste m to the adult branchial system has occurred. The yolksac serves as a supplemental source of nutrition as the embryos develop their external food-gathering abilities. The skeletal and sensory systems are suffic iently developed to allow the young to return to the safety of the fem ale's buccal cavity. Pigmentation may provide disruptive colouration. The rate and pattern of development of another mouthbrooding cichlid, Oreochromis mossambicus, is similar to that of P. philander despite th eir phylogenetic differences, and may be a consequence of similar life -history styles.