Growth and Energy Expenditures of Eurasian Perch Perca fluviatilis (Linnaeus) in Different Temperatures and of Different Body Sizes
To calculate the theoretical daily energy requirement of fish, information about the daily growth increment and the amount of digestible energy needed (DEN) to obtain one unit of biomass gain is required. The thermal unit growth coefficient (TGC) can be used for estimation of the daily growth increment. TGC is thought to be less affected by body size of the fish and temperature than the specific growth rate (SGR). However, there are some indications that the TGC may not be as stable as previous studies have shown. Furthermore, according to the theoretical background, DEN should increase as fish body size increases and with temperature. However, some data indicate that the DEN for percid fish may be unaffected by both these factors. The main objectives of this study was to estimate the effects of temperature and fish body weight on growth (TGC and SGR) and digestible energy need (DEN) of the Eurasian perch Perca fluviatilis (Linnaeus). In two separate laboratory experiments, feed intake, growth and energy expenditures were measured at either different temperatures (8.5-27.1oC) or for fish of different body sizes (20-110g). TGC and SGR proved to be affected by temperature and body size of the fish, while DEN was only affected by body size. The advantages with TGC for growth model construction thus seem to be less apparent than earlier believed. Thus, for evaluation of the theoretical daily energy requirement of fish, a growth model including both temperature and body size of fish, and an energy expenditure model including body size of fish is required.