Energetics and survival of virgin and repeat spawning brown trout (Salmo trutta)

Smaller virgin spawners of a stunted population of brown trout (Salmo trutta) had higher specific energy content than repeat spawners, indicating that once maturation has started, the trout does not completely recover from its first spawning. Males had higher amounts of total and specific energy after spawning compared with females (adjusted for length differences). The greatest energy expenditures were recorded among spawning females (specific total energy losses of about 20%, which were twice the losses of male spawners). Repeat females lost 40% of their fat content. The gonads of the females accounted for 20% of the total protein content. The loss in carcass protein and fat for the spawners was greater than the corresponding loss in visceral fat and protein. Survival rates paralleled the amounts of energy expended in reproduction. Overall survival rate of first-time spawning males (females) was about 0.90 (1.00), while the corresponding value for repeat spawners was about 0.65 (0.50). It is predicted that brown trout from a stunted population should make a relatively small investment in reproduction and thus represent a case of low investment among iteroparous fish species.