The influence of interaction between light intensity and tank wall colours on survival and growth of perch larvae (Perca fluviatilis L.) was investigated for 15 days after hatching. Three light intensities (250, 400 and 800 lx) and four wall colours (black, dark grey, light grey and white) were used. At the end of the experiment, survival rates ranged between 1% and 26%, and varied according to the different treatments (P=0.0001; df=11). A global effect of light intensity was detected (P=0.0001; df=2) and the highest survival rate was observed under 250 lx. Survival was also influenced by the tank wall colour (P=0.0001; df=3): light grey showed the best result (17%). The greatest growth in weight and length was observed in tanks with light grey and white walls, which were strongly illuminated, while the lowest growth was recorded in the tank with black walls and 250 lx illumination.

For 8 weeks, perch (22-25 g) were reared in a water recirculated system (WRS) and in floating cages (FC), and fed with an artificial food for trout. These two culture systems resulted in similar specific gron'th rates ( I . 1-1.4 %/day). However, at 4 Yo feeding rate, WRS ensured higher survival rates (90-100 Yo) vs. FC (70-80 YO), better food conversion indices (3.0 vs 4.1) and lower growth variability. WRS appeared more adapted to raise perch than FC. Nevertheless, sexual growth dimorphism in favour of females existed in WRS with restricted feeding rate (2 YO body weight per day). Likewise, this preliminary study suggested an effect of the rearing system on the perch body composition.

The effects of the size of food particles on the uptake of an artificial diet by perch (Perca fluviatilis) larvae, reared in tanks for 15 days following hatching, were studied. Perch accepted a dry diet with particles smaller than 200 mm. Average survival rates ranged from 11 to 25 % with daily specific growth of 0.03 mm and 0.08 mg in length and weight, respectively. There were no significant differences in the growth of perch fed with food particle sizes in the ranges 0 -80, 80 -125, 125-160 and 160-200 mm. The best results were obtained, nevertheless, with particle sizes smaller than 125 mm during the first week and larger than 125 mm in the second week. The mouth size of larvae doubled from 0.36 to 0.75 mm and showed a significant and positive correlation with larvae length. At the and of the experiment, the lipids content in larvae was measured, especially the triacylglycerols fraction. The saturated and mono-unsaturated fatty acids in larvae reflected those in their food. The unsaturated C22 : 6 (n-3) and C18 :2 (n-6) were the main component of n-3 and n-6 fatty acids series in perch.

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