ENERGY ALLOCATION IN POLYMORPHIC BROWN TROUT

1. To evaluate differences in energy allocation to gonadal development of resident and anadromous Brown Trout, Salmo trutta, we analysed tis sue composition and energy contents of adults of the two morphs from t hree small streams in southernmost Norway. Somatic energy per unit mas s of anadromous spawners (5.0 +/- 0.6 kJ g(-1) wet weight) was 1.1 tim es that of the residents, This difference was chiefly due to a 1.4-tim es higher lipid content in anadromous (4.9 +/- 1.5%) than resident tro ut. The somatic protein and carbohydrate contents per unit mass were h igher in resident than anadromous fish. 2. Somatic energy content per unit mass increased linearly with body length in resident but not anad romous fish. This increase was due to a significant increase in lipid content with fish size in resident contrary to anadromous trout.3. The mass-specific energy content of the ovaries was higher for residents (8.4 +/- 0.4 kJ g(-1) wet weight) than anadromous (7.81 +/- 0.5 kJ g(- 1) wet weight) trout. This was due to higher lipid and protein content s per unit mass in resident than anadromous females. In males, no simi lar differences between morphs were found (5.9 +/- 0.8 kJ g(-1) wet we ight), The mass-specific energy content of the ovaries was c. 1.4 high er than that of the testes, mainly caused by a 2.3-2.6 higher lipid co ntent per unit mass of eggs. 4. The mean gonadosomatic index (kJ %) wa s higher in anadromous (34.0 +/- 9.4) than resident (28.6 +/- 5.5) fem ales, but not in males (approximate to 3%). In females, but not in mal es, gonadal energy increased linearly with increasing somatic energy o f the fish. 5. Female gonadal energy at corresponding somatic energies was higher than that of males. On average, the energetic investment i n gonads relative to soma of first-time spawners in the year of matura tion was estimated at 11 % in males and 67% in females.