Life history strategies of diadromous and landlocked populations of the spotted galaxias, Galaxias truttaceus Valenciennes in Tasmania

摘要

A field study was carried out over a period of 20 months to investigate variation in life history traitsudof the spotted galaxias, Galaxias truttaceus. A comparison was made between two landlockedudlacustrine populations from the Central Plateau of Tasmania and two riverine diadromous populationsudfrom the Tasman Peninsula in south-east Tasmania.udUnivariate and multivariate analyses of serial counts and morphometric measurements revealedudvariation among populations in numbers of fin rays, gill rakers and measurements associated withudfins. Differences were more pronounced between fish from different habitat types (creeks versusudlakes) than within habitat types.udGonadal development of both sexes of fish from all localities commenced at the beginning ofudsummer (December). Riverine fish spawned at the end of autumn (May), however, lacustrine fish didudnot spawn until early spring (September). Temperature is thought to be a major factor influencing theuddelay in spawning of lacustrine fish. The gonads of lacustrine females continued to grow after theudriverine fish had spawned and a comparison offish prior to spawning revealed a greater investment inudreproduction in lacustrine females than riverine females in terms of weight of gonad relative to bodyudweight. From the conversion of proximate constituents to energy values, reproductive investment inudterms of the relative energy devoted to the gonad produced a similar result. Greater somatic fat (and therefore energy) reserves were accumulated by lacustrine fish overudsummer than riverine fish and greater depletion of these reserves occurred during gonadal maturationudof lacustrine fish. At peak levels, larger amounts of fat were incorporated into ovaries of lacustrineudfemales than in those ofriverine females. Ovaries generally possessed a larger percentage of fat thanudtestes while testes had a greater percentage of water, protein and ash.udThe relatively greater reproductive investment demonstrated by lacustrine fish was not apportionedudin the same manner between lacustrine populations. Females from one population produced largerudeggs whilst in females from the other population the fecundity increased at a greater rate with bodyudsize, in one year of the study. An analysis of life history traits within the galaxiid family affirms theudexistence of two distinct life history strategies. Diadromous galaxiids spawn before winter, haveudsmall eggs and produce large number of eggs, probably related to the overall larger body size of thisudgroup. Totally freshwater galaxiids generally spawn after winter, have larger eggs and produceudsmaller numbers of eggs, which may reflect the overall smaller body size of this group. Although theudspawning times of G. truttaceus from different habitats were consistent with those found in galaxiidudspecies, egg size, fecundity and body size were not.