As part of research-work on the usefulness of the bluegill sunfish, Lepomis macrochirus Rafinesque, as an experimental standard animal in fisheries research, we have tried to find out a way of obtaining its fingerlings throughout the year-curriculum. In sequence to the previous study on the breeding habits, some examinations have been conducted mainly on the developmental stages and the growth from the egg till one year after the hatching, using spawned eggs by full three or four year old fish in rearing tanks. The results so far obtained are as follows:
(1) The egg is adhesive and spherical in shape, measuring about 1.23 mm in diameter, with one large oil-globule (ea. 0.38 mm) and many minute ones.
(2) The egg diameter varies in the individuals and also in the batches of the same fish. However, no certain relation was found between the egg diameter and the age, the size and the number of times of spawning of the mother fish nor with the number of eggs spawned.
(3) The incubation period was about 40 hours (37-43 hours) at a temperature of 24.5°C, 28 hours (27-29 hours) at 28.5°C and 79 hours (75-85 hours) at 18.5°C, respectively. However, abnormal larvae appeared in a fairly high percentage (ea. 46%) at a temperature of 18.5°C, which is considered nearly out of the optimum spawning temperature.
(4) A percentage of fertilization and hatching of the eggs taken by the artificial insemination was fairly lower than those of the natural spawning.
(5) The newly hatched larva is about 3.23 mm in total length, with a yolk of 1.13×0.9 mm in size and no pigment in any part of the body.
(6) Cladocera (Morina sp.) seems to be most adequate food in the early stages of the bluegill larva, those fed with them showed faster growth than those fed by rotifers or copepods.
(7) The definite number of the spine and ray of each fin appeared at a total length of 13 mm, after that the lateral striped pattern appeared on the body side with the complete formation of the scale at a size of 14-15 mm in total length.
(8) From the examination of the size-frequency of the reared fingerlings, it was recognized that the phenomenon of "shoot individual" does not occur.
(9) The first year's growth of the bluegills is about 5.3 cm (3.0-8.3 cm). The average rate of growth of the female is below that of the male.