Abstract
Early life history is widely recognized as the stage of fish life history where mortality is the highest. Incorrect adaptation of early life-history characteristics to environmental conditions will result in high larval mortality and therefore recruitment failure. As a result, understanding early life-history requirements is critical if conservation techniques such as translocations are to be successful. For amphidromous fishes, landlocked and marine rearing environments present fundamentally different challenges, and thus early life history must be adapted to allow the establishment of landlocked populations. This study investigated gonadal development to determine spawning time, egg size, and fecundity in landlocked and diadromous populations of the threatened fish Galaxias brevipinnis to assess early life-history adaptation to facultative amphidromy in southern New Zealand. Ripening and spawning times of landlocked populations were protracted compared with diadromous populations. Diadromous populations simultaneously spawned during a March flood, whereas ovulating landlocked individuals were found from August to December, with a peak in October. Oocyte size in landlocked individuals was approximately 25% smaller than that in diadromous populations, and the fecundity of landlocked individuals was higher than that for diadromous individuals. Translocations of landlocked individuals to diadromous stocks are therefore unlikely to be successful, whereas the large egg size of diadromous populations would allow the translocation of diadromous stocks to landlocked environments.