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 conditions, the broods produced by females of the same age (three year old) and source population (Nalon basin, northern Spain), but having a wide egg size range in connection with maternal body size range (20.0 to 36.2 cm in fork length). Dry weight of eggs was positively correlated with female size (fork length or spawned weight), and accounted for most of the between brood variance in mean fry length 52 days after hatching (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 endurance times were positively affected by both fry fork length and original egg dry weight. Fry size also accounted for a significant amount 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 exhibited dependence on fry fork length. Further, decrease in swimming stamina after starvation was minimal for broods with larger mean fry length, whereas performance of smaller fish markedly diminished. Mean daily fork length increments of juvenile fish reared with siblings were lower than those of individuals of the same brood and similar size distribution 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 groups or effects of the greater variation of fish size in the mixed group than in the sole-sibling groups.