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¹ National Institute of Biology, Ljubljana, Slovenia
² Tolmin Angling Association, Tolmin, Slovenia DOI : 10.4194/1303-2712-v15_1_05 Viewed : 5276 - Downloaded : 4415 The size and composition of fish eggs are related to female’s characteristics, such as age, size and individual conditions, and they have an impact on the properties of offspring that are important for their fitness. Electron transport system (ETS) activity and respiration rate (R) of early life history stages (i.e. non-fertilized eggs, eggs at eyed stage and larvae with yolk sac) of 13 females of marble trout (Salmo marmoratus) were measured separately in order to determine their metabolic properties in relation to size. The results showed that larger females produced larger eggs in higher numbers. Growth experiments on the survival of offspring of a single female revealed that the survival rate of early embryos was higher for smaller eggs during the earliest stages, but ultimately the percentage of surviving larvae did not correlate with egg size. The ETS activities and respiration rates of non-fertilized eggs, eyed eggs and larvae differed significantly between 13 females. Both parameters increased with increasing dry mass of the early life history stages, but the increase of respiration rate was greater than that of ETS activity. The lower ETS/R ratios in larger individuals therefore indicate that their energy metabolism was less adaptable to environmental changes than that of smaller ones. Larger egg size could be an advantage under favourable conditions, whereas smaller size could be optimal under stressing circumstances in which the higher metabolic potential enables production of the energy required for metabolism. This is first report on the relationship between ETS activity and respiration rate of the early life history stages in salmonids. Keywords : Fish, ETS activity, ETS/R ratio, fitness, metabolism