Effect of salinity on growth of juvenile Yarra pygmy perch (Nannoperca obscura: Percichthyidae)

Abstract The threatened Yarra pygmy perch (Nannoperca obscura) is an obligate freshwater fish endemic to the south-eastern coast of mainland Austra-lia, where a majority of river systems have been heavily modified since European settlement. The purpose of this garden study was to explore any relationship between the growth rate of juvenile N. obscura with respect to salinity. Trials were conducted encompassing perceived and potential ranges within the species ’ environment, through five salinity treatments and recorded growth after 8 weeks. Two brood-groups were trialed simulta-neously to observe any intrapopulation variance in phe-notypic response potentially linked to genetic variance. The salinity trials found a clear model indicating in-creasing growth for moderate salinities (i.e. 2.5– 7.5 ppt), therefore identifying the ideal salinity range for N. obscura juveniles. Phenotypic response between brood-groups was varied and inconsistent, potentially reflecting low genetic variability. With a limited genetic variance restricting adaptability, tolerance to a changing environment would be reduced. Therefore increased salinization and subsequent flushing events within hab-itats may be key threats to the species ’ survival