Effects of tank colour and light intensity on feed intake, growth rate and energy expenditure of juvenile Eurasian perch, Perca fluviatilis L.

Eurasian perch (Perca fluviatilis) is receiving increasing attention as a new species in freshwater aquaculture. Understanding perch behaviour and performance in culture is important to optimize the design and management of tanks, and other culture conditions. The objective of this study was to evaluate how different combinations of tank colour and light intensity affect the feed intake, growth and energy expenditure of juvenile perch. Feed intake, growth rate and energetic growth efficiency were measured using groups of perch exposed to different combinations of tank colour (white, grey or black) and light intensity (200 or 1100 lx). Six groups of six perch were exposed to each colour/light combination. The initial average weight (± SD) of the fish over all experimental rounds was 59.6 g (± 6.6). Perch in white and grey tanks ate more than the perch in black tanks (P < 0.05). Correspondingly, fish growth rates were higher in the white, than in the black tanks (P < 0.05). Feed intake was also affected by an interaction between light intensity and tank colour (P < 0.05). Feed intake increased from dark to light tanks only under low light conditions. The results indicate that the higher feed intake in lighter tanks was the result of increased feed visibility, probably due to the feed's higher contrast against the background colour of the tank. Energetic growth efficiency did not differ between treatments, indicating that none of the colour/light combinations was more stressful to the fish. It is concluded that both tank colour and light intensity are important factors to consider when optimizing the performance of perch in culture.