Variability in length-at-age of marine species of fish was studied usi
ng age and growth data and population-specific life history and enviro
nmental parameters for 168 species in 50 families (458 records). The s
hapes of distributions, the magnitude of variability, the patterns of
variability with age and size, and the degree of overlapping of distri
butions were investigated using simple as well as multivariate statist
ical methods. Departure from normality was a widespread phenomenon. Th
e most important pattern of variability was an increase to a maximum a
t an intermediate age or size followed by a decrease. The degree of ov
erlapping was generally high, with only one or two distributions not s
ignificantly overlapped in most cases. The implications of these resul
ts for length frequency analysis and other areas of fisheries are disc
ussed.