The biology of a landlocked form of the normally catadromous salmoniform fish Galaxias maculatus (Jenyns). I. Life cycle and origin

Abstract

In contrast to most other members of the family Galaxiidae which live and reproduce in fresh water, Galaxias maculatus, the common jollytail of Australia and "whitebait" of New Zealand, is normaIly catadromous throughout its range (south-eastern Australia, New Zealand, and southern South America). In some athalassic inland lakes on the volcanic plains of south-western Victoria, however, a number of populations apparently descended from this species have becomelandlocked. The life cycle of the forminhabiting one of these lakes (the "landlocked jollytail" of Lake Modewarre) may be briefly summarized as follows: Gonadal maturation in the adult fish, which live in the slightly saline landlocked lake, begins around March and is almost completed by about June. The final stage of maturation is not reached, however, until these fish migrate short distances up intermittent inflowing creeks when the latter begin to flow in late winter and spring (July-October). Spawning takes place when the creeks are swollen after heavy rain, the eggs being deposited amongst flooded vegetation in shallow areas of slow-flowing water along the creek banks. Many of the spent fish die after spawning. The eggs, which are stranded when the flood-waters subside, develop amongst the vegetation on the banks above the normal water level. After development is complete reimmersion by the first flood to cover them stimulates hatching. The normal developmental period is probably about 2 weeks, but in the absence of flooding hatching can be delayed up to at least a month after fertilization. The newly hatched larvae are washed downstream into the lake where they feed and grow to maturity. They migrate upstream to spawn in the following late winter-early spring season at an age of approximately 1 year. The fish grow to about 9 cm in their first year, 14 cm in their second, and 17 cm in their third year. The average size of the females is greater than that of the males. The general features of the life history of this landlocked form are compared and contrasted with those of the stream-dwelling species G. maculatus and a number of other salmoniform fishes. The geological origin of the complex of lakes in south-western Victoria inhabited by landlocked galaxiid populations is discussed, and an hypothesis concerning the origin of the Lake Modewarre form from an ancestral population of G. maculatus in the Barwon-Leigh River system is advanced.