Influence of the Stimuli Provided by the Male Cichlid Fish, Tilapia macrocephala, on the Spawning Frequency of the Female

Abstract

To examine the influence of stimuli provided by the d1 on the spawning frequency of the , pairs of Tilapia were placed in the following 6 experimental situations:[long dash](1) and together in a single aquarium (control). (2) separated from [female] by a transparent fence which divided the aquarium into 2 equal halves. (3) separated from J by a transparent partition. (4) separated from by an opaque partition. (5) and [female] in separate aquaria in which the adjacent walls were transparent. (6) and [female] in separate aquaria in which the adjacent walls were opaque. Each of these 6 conditions was duplicated 9 times and a record was taken of all spawnings during an entire yr. The expt. revealed that completely isolated [female][female] will continue to spawn at infrequent intervals, and that the sight of a d markedly increases this spawning frequency. There was some indication that in addition to the visual stimuli, chemical or vibratory influences increase slightly the oviposition rate. Since egg laying is an indication of prior ovulation, Tilapia is intermediate between those animals which ovulate spontaneously, and those requiring sexual exteroceptive stimulation before they will ovulate. It is pointed out that many vertebrates could be placed in this intermediate category, and that the division between spontaneously and non-spon-taneously oyulating vertebrates is not as sharp as is generally described.