Effects of river impoundment on body condition and reproductive performance of the Australian native fish, Macquarie perch (Macquaria australasica)

This study attempts to evaluate the influence of the impounding of Lake Dartmouth (36°35'S, 147°31'E; on Mitta Mitta River in Victoria) on the Macquarie perch (Macquaria australasica, Cuvier 1830), an Australian percichthyid fish of riverine origin. In this study the yearly changes in body condition and spawning performance of adult populations in the impoundment were evaluated in relation to lake features, in particular the water level. Body condition of the spawning population of Macquarie perch in Lake Dartmouth, in year n was related to mean annual storage volume of the lake, with a time lag of one year during the post-filling phase of the lake (1991-1997). The influence of condition on the reproductive performance of captive female Macquarie perch from Lake Dartmouth using artificial propagation techniques was evaluated over the period 1991-1997. The mean relative fecundity (mrf), expressed as the number of eggs produced per kilogram of body weight of hypophysed fish, showed a decrease over the period, but the mean weight of hypophysed fish did not decrease over the same time period. The mrf (Y mrf ) was positively correlated to yearly mean relative condition factor (X Rc ), the relationship being: Y mrf =68692 X Rc -43955 (R 2 = 0.58, P < 0.05). The spawning variables, mean percentage fertilization (Y fn ) (1991-1997) and mean larval production (Y fn ) (1992-1996) in each year (n) were also related to the mean relative condition factor (X Rc ) of female fish that spawned after hypophysation in each year. It is suggested that the declining success in the artificial propagation of this species is caused by a declining maternal condition of female fish collected from the impoundment, resulting from poor nutrition.