Effects of Warming and Food Quality on the Metabolism and Growth of an Algivorous Fish from Lake Tanganyika

Lake Tanganyika has warmed ~1 °C over the last century, potentially threatening its unique biodiversity. In addition to the direct effects of warming, algivorous animals may face a decline in nutrient content of their food due to reductions in upwelling from the hypolimnion. We used a factorial lab experiment to quantify the effects of temperature and food quality on relative growth rate (RGR) and metabolism of an algivorous cichlid, Tropheus duboisi. In all temperature treatments, RGR of juveniles fed a low quality diet was 0.6x that of fish fed a high quality diet. Fish acclimated to high temperature (32°C) grew at nearly half the rate of their counterparts at 26 °C or 29 °C, but growth efficiency and RGR were comparable at 26 °C and 29 °C. Neither temperature nor food quality had a detectable effect on basal metabolism. Our results suggest that T. duboisi is a relatively eurythermal species but could be strongly affected by declining algal nutrient content. Thus, the indirect effect of climate change on food quality may outweigh increases in metabolism associated with lake warming.