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

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