Effects of suboptimal temperatures on larval and juvenile development and otolith morphology in three freshwater fishes: implications for cold water pollution in rivers

Temperature is a key determinant that governs fish survival, reproduction, growth and metabolism. In freshwater ecosystems, anthropogenic influences have resulted in acute and prolonged temperature changes which lead to lethal and sub-lethal impacts on the biota that occupy these environments. We assessed the effects of temperature on somatic and otolith growth and development of three species of native Australian freshwater fish (silver perch Bidyanus bidyanus, trout cod Maccullochella macquariensis and golden perch Macquaria ambigua) to simulate how thermal pollution from the release of unseasonably cold water from thermally stratified dams in Australian freshwater ecosystems may impact fish at critical life-history stages. Fish (31 days post-hatch) were exposed to four temperature treatments (13, 16, 20, 24 degrees C) for 30 days. Low temperatures resulted in reduced somatic growth, with no growth observed in silver perch and golden perch held at 13 degrees C over 30 days. Somatic growth was highest at the upper temperature of 24 degrees C. Morphological assessment of fish size reiterated that low water temperatures resulted in reduced body size, particularly in terms of body width and head size. Low temperatures were associated with reduced otolith growth in all species, however a somatic-otolith size relationship was maintained for all species in measures of otolith weight, area, length and perimeter. The sub-lethal impacts observed in our study are likely to manifest at the population level through a reduced capacity of larvae and juveniles to avoid size-dependent predation, a narrower range of prey sources due to extended gape-limited feeding and, ultimately, poorer survival and recruitment.