Michigan Department of Natural Resources
Fisheries Research Report No.1819, 1975
Sexual Maturity and Fecundity in Brown Trout of the Platte River
Clarence M. Taube
Abstract.-Sexual maturity in brown trout of the Platte River begins in males when they are between 177 and 202 mm (7 and 8 inches) in length, and in females essentially when they are between 202 and 228 mm (8 and 9 inches). At these sizes, incidence of maturity in the two sexes was the same, 35%. At age I, 32% of the males and 16% of the females were mature. Incidence was virtually 100% in males when they reached 253 mm (10 inches) or age III, and 100% in females at 304 mm (12 inches) or age IV . In the length range of 202-354 mm (8-14 inches), the average number of eggs produced per female trout by inch group ranged from 241 to 936. The largest number found among 89 fish (202-472 mm or 8.0-18.6 inches) was 2,419. Although fecundity varied widely between individuals of similar size and identical age, it was as a whole positively correlated with both size and age. The formulas for regression of egg number on length are: N = 7.3 (total length, mm) -1498.8 and N = 186.1 (total length, inches)-1,498.8. The formula for egg number by age is: N = 353.3 (age group)-155. 7. Size of eggs also varied considerably between individual fish, but like fecundity, it was correlated with size and age of females; that is, the larger and older females produced the larger eggs. Average diameter of eggs from brown trout collected in September ranged from 3.2 to 4.8 mm.