Differences in egg number and egg size within a wild population of white-spotted char (Salvelinus leucomaenis) were examined from the perspective of maternal growth history by using a back-calculation method. Relatively greater egg size variation occurred among females (61.6%) than within females (38.4%). Larger females produced a larger number of eggs, which were also larger in size. To understand the causes of variation in egg number and egg size, several contributory factors determining maternal size were considered (initial size, growth rate for each age, total age). Egg number was not associated with maternal growth history. Contrary to egg number, egg size was strongly associated with maternal growth history; high growth in the first year was negatively associated with egg size, but high growth in the second year was positively associated with egg size. The results indicated that white-spotted char potentially exhibit phenotypic plasticity in egg size according to their growth history.

The relationships between fecundity, egg size and female size of sea-run form were compared with resident form, using white-spotted charr, Salvelinus leucomaenis. Both fecundity and egg size increase with female size. However, the relationship between egg size and female size differed significantly between the resident and sea-run forms. Egg sizes of sea-run and resident were similar even though sea-run fish were much larger. 1998 The Fisheries Society of the British Isles

SUMMARY : The ages of individual specimens of white‐spotted char Salvelinus leucomaenis, collected from the Furuu River in Hokkaido, Japan, were determined from otoliths using NIH Image. We employed two methods to determine age. First, for a surface method (traditional method), the ages were made from examinations of otoliths under a microscope by experienced readers A, B and an unexperienced reader C. Second, for an auto‐counting method, a computer program was used to detect the peaks from otolith images. We made a mathematical model to estimate the probability of a correct reading for each reader, using the results of the age determination and the per cent age agreement among readers. The ability to determine the age of white‐spotted char depended on whether or not the reader had ever previously made age determinations. The ability of auto‐counting method was below that of reader A (one of the experts), and the method was slightly superior to reader B (the other expert).

No abstract