CHANGES IN PROXIMATE COMPOSITION AND ESTIMATES OF ENERGETIC COSTS DURING UPSTREAM MIGRATION AND SPAWNING IN ATLANTIC SALMON SALMO-SALAR

1. There were marked changes in the relative lipid content of somatic and visceral tissues during the course of upstream migration and spawn ing. The lipid content per 100 g wet tissue mass was high in maturing salmon in July (soma, pooled sexes: 12.1 g; viscera: 11.4 g in males a nd 7.3 g in females) and decreased to a minimum after spawning in Nove mber (soma: 2.1 g; viscera: 1.6 g). Percentages of protein in the soma and viscera were relatively stable during the study period, ranging f rom 21.9 g (soma) and 16.3 g (viscera) 100 g(-1) tissue in maturing fi sh in September-October, to 17.1 g (soma) and 16.1 g(viscera) in spent salmon. The carbohydrate content was relatively small, ranging betwee n 0.27 and 2.4 g 100 g(-1) wet tissue mass. 2. Application of energeti c coefficients suggested that the somatic energy content decreased fro m 814 kJ 100 g(-1) wet tissue mass in maturing salmon (pooled sexes) c aught in coastal waters in July, to 370 kJ in spent fish in the river in November. Visceral energy density decreased in the same period, fro m 706 kJ in males and 570 kJ in females to 340 kJ and 360 kJ, respecti vely. 3. Mean gonadosomatic index (GSI) values, in terms of energy of males, in July and just prior to spawning were 0.4 and 3.2, respective ly. The corresponding figures for females were 2.8 and 28.6. 4. Gonada l energy contents per unit tissue mass were estimated to be higher in females than males, except for spent fish. Prior to spawning energy co ntent was 845 kJ 100 g(-1) gonad wet mass in females and 375 kJ in mal es. After spawning the gonadal energy contents were 280 kJ and 385 kJ 100 g(-1) wet mass, respectively. 5. The relative energy, lipid and pr otein contents of somatic, visceral and gonadal tissues were highly co rrelated with percentage tissue water. 6. Total energy loss due to mig ration and spawning was between 60% and 70% of the body reserves prior to upstream migration. It was similar for males and females, but high er in large than small salmon. Estimated energy investment due to repr oduction correlated significantly with estimated survival rates in 12 Norwegian populations of Atlantic salmon.