| Summary: | Embryonic growth patterns and the development of fin rays were examined in pure and reciprocal crosses of planktivorous and small benthivorous morphs of arctic charr from Thingvallavatn, Iceland. Embryos were incubated individually in a controlled laboratory environment at 4.5°C water temperature. Planktivorus charr had larger eggs than small benthivorous charr and the progeny of the former were longer (total length) at days 125, 145 and 159 after fertilization. Size differences remained significant after the removal of egg size effect on embryo size. Size of hybrid progeny tended to be similar to their maternal pure progeny group, suggesting maternal effects not directly related to yolk volume. In general, fin ray number increased faster in small benthivorous charr progeny than in planktivorous charr progeny, hybrid progeny tending to have intermediate fin ray numbers. The results indicate that morph differences in embryonic growth and skeletal development have a genetic and maternal component. Results support the hypothesis that in the period from hatching until just after first external feeding small benthivorous charr may allocate more energy towards the development of structures required for manueuvering while planktivorous charr allocate more energy to body growth. The different developmental trajectories may reflect adaptations to discrete differences in habitats between the morphs. In Thingvallavatn four morphs of arctic charr, Salvelinus alpinus L., coexist. The morphs differ in habitat use, diet, life history and morphology. Genetic studies indicate that the morphs have evolved sympatrically within the lake. In order to assess the genetics of variation in bone development we reared pure and reciprocal crosses of the most abundant morphs, small benthivorous- and planktivorous charr in controlled experimental environment. Spawning fish were caught in Thingvallavatn and crosses made in the laboratory. Individual eggs were put into separate incubation cells and the embryos were kept there throughout the ...
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