EFFECTS OF EGG SIZE ON OFFSPRING DEVELOPMENT AND FITNESS IN BROWN TROUT, SALMO-TRUTTA L

To examine the effects of egg size on initial fry size and performance in brown trout (Salmo trutta L.) we reared, under common hatchery con ditions, the broods produced by females of the same age (three year ol d) and source population (Nalon basin, northern Spain), but having a w ide egg size range in connection with maternal body size range (20.0 t o 36.2 cm in fork length). Dry weight of eggs was positively correlate d with female size (fork length or spawned weight), and accounted for most of the between brood variance in mean fry length 52 days after ha tching (yolk fully consumed; 72% of variance explained by egg weight) and after 90 days (89%). Maternal size also significantly contributed to juvenile size at these stages of development. Mean brood swimming e ndurance times were positively affected by both fry fork length and or iginal egg dry weight. Fry size also accounted for a significant amoun t of the within brood variability in swimming stamina in the clutches with a wide range in fry size. Swimming performance after a short (six days) fasting period was lower than before starvation, but again exhi bited dependence on fry fork length. Further, decrease in swimming sta mina after starvation was minimal for broods with larger mean fry leng th, whereas performance of smaller fish markedly diminished. Mean dail y fork length increments of juvenile fish reared with siblings were lo wer than those of individuals of the same brood and similar size distr ibution reared at equal density with non-sibling conspecifics. However , our experimental arrangement did not allow discrimination of kinship effects from possible influences of shared early rearing of the kin g roups or effects of the greater variation of fish size in the mixed gr oup than in the sole-sibling groups.