1. In finfish larviculture, the tank wall colour (TWC) was already reported to have significant effect on the rearing effectiveness. This was related with the behavioral response of particular species to different TWC (e.g., Martin-Robichaud and Peterson 1998, Cobcroft and Battaglene 2009) and the visibility (contrast) of the food in the tank with different TWC (e.g., Martin-Robichaud and Peterson 1998). Martin-Robichaud and Peterson (1998) also proved that TWC affected swim bladder effectiveness (SBIE) in striped bass, Morone saxatilis (Walbaum). In Eurasian perch, Perca fluviatilis L., two reports were published to date as considering the effect of TWC on larvae rearing effectiveness: 1) Tamazouzt et al. (2000) - reported, that the black TWC affected significantly lower survival (3%) as compared to the white TWC (13% survival rate) up to the 15 DPH 2) Jentoft et al. (2006) - reported that black TWC had positive effect on the growth rate during first 5 weeks of earing. As can be seen, both of the reports indicated contrary conclusions. Also, none of those studies investigated the effect of TWC on the SBIE. References: Bein R. and G. Ribi. 1994. Effect of larval density on the development of perch larvae (Perca fluviatilis L.). Aquatic Sciences 56: 97–105. Bristow B.T., R.C. Summerfelt and R.D. Clayton. 1996. Comparative performance of intensively cultured larval walleye in clear, turbid, and colored water. The progressive Fish-Culturist 58: 1–10. Cobcroft J.M. and S.C. Battaglene. 2009. Jaw malformation in striped trumpeter Latris lineata larvae linked to walling behaviour and tank colour. Aquaculture 289: 274-282. Fontaine P. 2004. L’élevage de la perche commune, une voie de diversification pour l’aquaculture continentale. INRA Prouctions Animales 17: 189–193. Jentoft S., S. Øxnevad, A.H. Aastveit and Ø. Andersen. 2006. Effects of Tank Wall Color and Up-welling Water Flow on Growth and Survival of Eurasian Perch Larvae (Perca fluviatilis). Journal of the World Aquaculture Society 37: 313–317. Kestemont P. and C. Melard. 2000. Aquaculture. P.191–224. In: Percid fishes. Systematics, ecology and exploitation. J.F. Craig (Ed.). Blackwell Science, Oxford, UK. Martin-Robichaud D.J. and R.H. Peterson. 1998. Effects of light intensity, tank colour and photoperiod on swimbladder inflation success in larval striped bass, Morone saxatilis (Walbaum). Aquaculture Research 29: 539–547. Tamazouzt L., B. Chatain and P. Fontaine. 2000. Tank wall colour and light level affect growth and survival of Eurasian perch larvae (Perca fluviatilis L.). Aquaculture 182: 85–90. Żarski D., K. Palińska, K. Targońska, Z. Bokor, L. Kotnik, S Kreszeff, K. Kupren, A. Horvath, B. Urbanyi and D. Kucharczyk. 2011. Oocyte quality indicators in Eurasian perch, Perca fluviatilis L., during reproduction under controlled conditions, Aquaculture 311: 84–91. White tank wall colourBlack tank wall colour Hormonal treatment: hCG 500 IU kg -1 In vitro fertilization Controlled gametes collection Controlled incubation (14°C) Freshly hatched larvae (0.78±0.10mg, 5.22±0.55mm) were randomly divided into two groups (in triplicates) and stocked into experimental tanks with WHITE or BLACK wall coloures. In both treatments the same rearing conditions were provided: Tanks with volume 50 L; 25,000 ind. per tank; constant light (1500 lx); constant temperature (15°C); no surface skimmer; top water inlet (in the form of sprinkler). An experimental unit used for Eurasian perch larvae rearing (treatment with black TWC) -Larvae were fed with Artemia sp. (SF origin) from 5 DPH -On day 20 of the experiment the following parameters were recorded: -SBIE (%) -total length (TL, ±0.01mm) -wet body weight (WBW, ±0.1mg) -survival rate (on the base of the number of live larvae recorded) Tab. I. Final characteristic (TL – total length, WBW – wet body weight, SBIE – swim bladder inflation effectiveness) of Eurasian perch larvae reared for 15 days (from hatching) in the tanks with different tank wall colours: white (white TWC) and black (black TWC). Data (mean ±SD) in columns marked with different letters were statistically different (t-test, P<0.05). Eurasian perch larvae during swim bladder inflation in tank with black wall colour. The larvae were distributed in the middle of the tank, directly under the light source. Eurasian perch larvae during swim bladder inflation in tank with white wall colour. The larvae were distributed at the edge (next to the walls) of the tank The presented results for the first time clearly shows that the TWC affect the SBIE significantly, where bTWC was found to be more effective as compared to bTWC. The survival and SBIE of Eurasian perch larvae was reported to be very variable. The obtained in the present study in bTWC treatment survival rate was close to that reported by Jentoft et al. (2006) (approx. 25%) and higher than obtained by Tamazouzt et al. (2000) (max. 17%). The SBIE was also very similar to that reported by Bein and Ribi (1994) who recorded SBIE between 20.1 and 42.8%. Therefore, the obtained results, as well as the rearing conditions provided, may be considered as a satisfactory. The positive effect of the black TWC on the swim bladder inflation was already reported for the striped bass by Martin-Robichaud and Peterson (1998). Those authors suggested, that it was probably linked to the light reflection form the white TWC and thus attract the phototactic larvae better than the light above the water surface. The TWC were found to affect so called ‘walling behaviour’ in striped trumpeter, Latris lineata (Forster), larvae what resulted in high jaw malformations rate (Cobcroft and Battaglene 2009). In walleye, Sander vitreus (Mitchill), Bristow et al. (1996) recorded reduced ‘walling behavior’ in turbid water what positively affected SBIE. It may be concluded, that application of bWTC in the present study affected higher SBIE due to the prevention of ‘walling behaviour’ in Eurasian perch larvae. In effect, phototactic perch larvae swam to the source of light (located above the tank) rather than to the tank walls. This caused a direct contact with the water surface and allowed more effective passage through the water surface and gulp the air. The aim of the present study was to determine the effect of white and black TWC on the SBIE in Eurasian perch, which is one of the very promising candidates for diversification of European intensive freshwater aquaculture. Eurasian perch larvae with inflated swim bladder.Eurasian perch larvae without inflated swim bladder.