INTENSIVE CULTURE OF JUVENILE AND ADULT EURASIAN PERCH (P-FLUVIATILIS) - EFFECT OF MAJOR BIOTIC AND ABIOTIC FACTORS ON GROWTH

Recent developments in Eurasian perch (Perca fluviatilis) larval reari ng and weaning techniques allow large-scale intensive rearing tests, b oth with juveniles and adults. This review presents the results of exp eriments conducted in a commercial scale production environment (0.5-1 .6 m(3) flow-through tanks) and focuses on the most relevant factors i nfluencing growth and production in intensive rearing systems. Combine d effects of food ration and temperature showed that the maximum growt h rates (0.06-1.80 g fish(-1) day(-1) for 1-300 g fish) were observed at 23 degrees C. The thermal range for intensive rearing of perch exte nds at least down to 11 degrees C (growth rate equivalent to 29% of th at observed at 23 degrees C). The maximum daily food ration (9-4.5% li pid; 57-44% crude protein) at 23 degrees C resulted in feed conversion rates from 1.1 to 2.0 in fish ranging from 1 to 150 g and was modelle d as follows (R(2) = 0.89): R(max) (% day(-1)) = 7.60 w (weight, g)(-0 .31). Juvenile (1-15 g) perch reared at 10000 fish m(-3) showed a grow th rate of 0.2 g fish(-1) day(-1), thus 67% higher than at 400 fish m( -3). In the most intensive rearing trials (124 kg m(-3)), the maximum production rate observed was 2.6 kg m(-3) day(-1). Growth heterogeneit y constitutes a major constraint in perch culture. Size grading experi ments resulted in the emergence of fast-growing fish in each sorted gr oup. In addition, the sorting process caused the productivity to be sl ightly lower (5-6%) than in non-sorted populations of the same origin and body weight. Mass mortality may take place at any stage of perch r earing within the 1-200 g body weight range. In general, an overall 50 % survival rate was recorded after 14 months. Parasites, bacteria and fungi were the most frequently encountered causes of mortality. The oc currence and impact of diseases were largely reduced in recirculating systems where the survival rate is 70% higher than the values observed in flow-through rearing systems. In intensive rearing systems at 23 d egrees C and at maximum stocking biomass of 50 kg m(-3), 44-day- old w eaned perch juveniles (ranging from 0.5 to 1 g initial body weight) re ached an average body weight of 130-150 g after 1 year of rearing. Sti ll, this marketable size was reached about 3 months earlier by fast gr owing individuals within the population. The intensive culture of perc h at a constant 23 degrees C water temperature allowed much higher gro wth rates than usually observed in conventional, extensive systems und er natural thermal regimes. Constant temperatures also inhibited the s exual maturation in females. Further improvements in growth and produc tivity in intensive perch rearing will closely rely on techniques such as the selection of fast-growing strains, monosex female or sterile t riploid fish production.