Variation in the life History of Diadromous and Lanlocked populations of the Spotted Galaxias, Galoxias truttaceus Valenciennes, in Tasmania

Abstract

Variations in life history traits such as age class distribution, growth, gonadal development, reproductive investment and spawning time were studied in two stream-dwelling diadromous and two landlocked freshwater lake populations of the spotted galaxias, Galaxias truttaceus, in Tasmania. Whereas stream populations were dominated by 0+, I+ and 2+ age-class fish, lake populations had a smaller proportion of these younger individuals and a larger proportion of age classes older than 2 +. Growth in both lake and stream populations was slow over winter and more rapid during spring and summer. The majority of fish of both sexes matured at age two, irrespective of size, although some lake-dwelling males matured in their first year. Gonadal development commenced at the beginning of summer (December) in all populations. Spawning in stream-dwelling populations occurred before winter (May) and was associated with decreasing water temperature and photoperiod. By contrast, landlocked populations spawned in early spring (September), at which time both temperature and photoperiod were increasing. At spawning, landlocked females invested more energy in reproduction than did riverine females. This appeared to be a function of larger egg size in females from one lake population and greater fecundity in females from the other. Although G. truttaceus fits the general life-history model for diadromous galaxiids, having relatively large numbers of small eggs, the shift in spawning time for landlocked populations, and the inter-population variations in egg size and fecundity suggest considerable flexibility in the characteristics of this species' life history.