. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. DEVELOPMENT OF STEELI1KAI) TKOUT EGGS 251 not the case and g'ave nnu-li useful data of his own. Table 1 has been made up from tliese (hita and sliows how great are the variations in temperature units at different water temperatures. From it, it appears that temperature units are not a safe measure for the trout culturist. For that reason they are not sliown on the graph in figure 69 of tliis paper, but they are ineluded in tlie sectio
. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. DEVELOPMENT OF STEELI1KAI) TKOUT EGGS 251 not the case and g'ave nnu-li useful data of his own. Table 1 has been made up from tliese (hita and sliows how great are the variations in temperature units at different water temperatures. From it, it appears that temperature units are not a safe measure for the trout culturist. For that reason they are not sliown on the graph in figure 69 of tliis paper, but they are ineluded in tlie section on the description of daily egg samples and in the drawings, for the benefit of those who are accus- tomed to thinking in such terms. 20 DAYS SINCE FERTILIZATION 30 40 50 60 100 .80 60 jao 70 T 80. ^ MATCHING OOMPLCTED HATCHING BEGINS VENTRAL FINS APPEAR TRACES OF BLACK PIGMENT ON HEAD ANO BODY TENDER STAGE ALMOST FINISHED EtES BEGIN TO BE VISIBLE TAIL NOW HETEROCERCAL CAUDAL REGION APT TO BE TWISTED Fig. 69. Number of days required to bring -steelhead eggs to different stages of development at various temperatures. The 51° data based on experiments by J. H. Wales. Data for development at other temperatures are iiypothetical: total incubating periods are based on Embody's (1934) tables; percentages of development based on the assumption that the earlier developmental stages are in straight-line relationship to the total incubation periods at the various temperatures. In any species of trout, the incubation period or average hatching time of the eggs is not immutably fixed for a given temperature but may vary as much as six days between egg lots taken from ditferent parent fish. However, our figure for the number of days required to hatcli the steelhead eggs considered in this study was almost identical Avith that of Embody's for rainbow trout at the same average tem- perature. (See table 1.) The time from the hatching of the first to the hatching of the last egg in a
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