Changes in metabolic rate, excretion, energy reserves, and starvation response of diploid and triploid Salvelinus fontinalis and diploid O. mykiss after long-term exposure to elevated temperature

Abstract

Routine metabolic rate (RMR), faeces composition, quantities of dissolved excretion, and energy reserves were investigated in diploid (2n) and triploid (3n) Salvelinus fontinalis and 2n Oncorhynchus mykiss exposed to 20°C for 32 d in comparison to fish acclimated to 9°C. At 20°C RMR of 2n S. fontinalis decreased with increasing exposure time and after 32 d it did not differ from 9°C. Also in O. mykiss RMR decreased with exposure time but remained 60% higher than at 9°C. In 3n S. fontinalis exposed to 20°C RMR was constantly increased for 120%. For all species/ploidy levels faeces dry weight and phosphorus concentration and quantities of excreted dissolved nitrogen and phosphate did not differ between 9°C and 20°C. Lipid concentration of faeces was decreased at 20°C. With exception of O. mykiss also protein of faeces was decreased at 20°C. In all species/ploidy levels liver glycogen and visceral fat was decreased at 20°C, while liver triglycerides and adenylate energy charge were not affected. In 2n and 3n S. Salvelinus temperature related responses to 5-d starvation were investigated. In 2n S. fontinalis RMR decreased in starving fish in comparison to fed ones at 9°C and increased at 20°C. RMR of 3n S. fontinalis did not change. For both ploidy levels, dissolved excretion was decreased due to starvation at 9°C and 20°C. Visceral fat was decreased due to starving at 9°C, liver glycogen and triglycerides at 20°C. The data are important to manage the impact of increased water temperature on salmonid aquaculture.