1. AMMONIA EXCRETION IN JUVENILE TENCH TINCA TINCA DURING THE INTENSIVE REARING UNDER LABORATORY CONDITIONS Joanna Nowosad 1 *, Daniel Żarski 1, Maria Biłas 1, Katarzyna Dryl 2, Sławomir Krejszeff 1 Dariusz Kucharczyk 1 1 - Department of Lake and River Fisheries, University of Warmia and Mazury in Olsztyn, ul. Oczapowskiego 5, pok. 327, 10-719 Olsztyn, Poland * corresponding author e-mail: nowosad.joanna@gmail.com 2 - Department of Gamete and Embryo Biology, Institute of Animal Reproduction and Food Research of Polish Academy of Sciences, Olsztyn, Poland INTRODUCTION Common tench, Tinca tinca (L.), is one of the most important commercial freshwater species in many European countries and is one of the most important candidates for diversification of freshwater aquaculture (Gela et al. 2006; Kujawa et al. 2011; Mamcarz et al. 2011). However, in conditions of traditional pond aquaculture tench is characterised by a slow growth rate compared to other cyprinids. However, the constantly growing interest in this fish is an inducement for development of work on improving culturing in recirculating aquaculture systems (RAS), which may lead to an increase in production effectiveness for this fish species. However, there is limited data regarding ammonia excretion in different size juvenile tench that would allow to design feeding and effective rearing protocols in RAS. The aim of this research was to determine the amount of excreted ammonia in juvenile common tench of different size, reared under controlled conditions. MATERIAL AND METHODS Tench larvae were obtained by means of artificial reproduction with the use of hormonal injection (1 Ovopel pellet kg -1 ) (Horvath et al. 1997). Next, larvae were reared for 55 days (27°C). First 35 days fish were fed ad libitum with Artemia nauplii and the next 20 days with commercial feed solely (54% protein, 18% fat, 8% carbohydrates) at the dose of 9% of biomass daily (3 times a day). During the experiment (the next 28 days) fish were fed with the same feed and doses. Every 7 days, after the morning feeding, 10 fish were moved to the test beaker (1 L) filled with clear water and gently aerated. After the 11 h ammonia was measured in each beaker. The same procedure was repeated 4 times in every 7 days. After the test the fish were measured (0.1 mm) and weighted (0.01 g). Experiment was conducted in triplicates. The obtained results were recalculated to the amount of excreted ammonia per 1g of fish (mg g -1 ). Additionally, SGR (% day -1 ) was calculated for every week of experiment.RESULTS Initially, the mean weight (W) of the fish amounted to 0.18 ± 0.04 g and in the last measurement it was 0.36 ± 0.09 g. Body length (Lt) amounted to 24.9 ± 1.7 mm and 30.3 ± 2.3 mm at the beginning and the end of the experiment, respectively, and was statistically different. Despite the growth of fish and the increased values of the rearing coefficients and parameters in the successive weeks of the measurements. The ammonia amount excreted by the fish at the end of the day (on which the test was conducted) was at the same level within both the control and the experimental group (Table 1).Parameter Day of rearing day 181522 Body weight (g)0.18±0.04 b 0.22±0.06 b 0.27±0.1 ab 0.36±0.09 a Body length (mm)24.9±1.7 c 26.5±2.0 bc 28.1±2.8 ab 30.3±2.3 a Fulton’s condition factor (K) 1.14 ±0.081.14 ±0.111.18 ±0.081.26 ±0.09 SGR (% day -1 )-2.75±0.313.18±0.573.81±1.67 Ammonia excreted (mg g -1 ) 0.37±0.010.37±0.040.37±0.030.39±0.01 Fig. 1: Juvenile tench 69 days post hatching (DPH) Table 1: Parameters of juvenile tench reared under controlled conditions over the course of the experiment. Data expressed as the mean ± SD. Data in rows marked with different letters were statistically different (p<0.05) DISCUSSION The results obtained in this paper suggest that the amount of ammonia excreted by fish per weight unit in the analysed period does not depend on fish size and that the biomass of the reared fish is the only factor which can influence the ammonia content in water. Thus, it may be suggested that quantity of ammonia in RAS during the intensive rearing of juvenile tench is strictly related to the fish biomass rather than fish size (as it was supposed to date). This is particularly important due to the fact that biological filtration capacity depends on the amount of ammonia supplied to the filtration medium (Żarski et al. 2010). References Gela D, Flajshans M, Kocour M, Rodina M, Linhart O (2006) Tench (Tinca tinca) broodstock management in breeding station under conditions of pond culture a review. Aquacult Int 14:195–203 Horvath L, Szabo T, Burke J (1997) Hatchery testing of GnRH analogue-containing pellets on ovulation in four cyprinid species. Pol Arch Hydrobiol 44:221–226 Kujawa R, Kucharczyk D, Mamcarz A, Żarski D, Targońska K (2011) Artificial spawning of common tench Tinca tinca (Linnaeus, 1758), obtained from wild and domestic stocks. Aquacult Int 19:513–521 Mamcarz A, Targońska K, Kucharczyk D. Kujawa R. Żarski D (2011) Effect of live and dry food on rearing of tench (Tinca tinca L.) larvae under controlled conditions. Ital J Anim Sci 10:42–45 Żarski D, Kucharczyk D, Targońska K, Krejszeff S, Czarkowski T, Babiarz E, Nowosielska DB (2010) Dynamics of nitrogen and phosphorus in closed and semi-closed recirculating aquaculture systems during the intensive culture of goldfish, Carassius auratus auratus (L.), juveniles. Arch Pol Fish 18:187–193 www.eng.InnovaFish.pl AKNOWLEDGMENTS This study was co-financed by the project “Innovations in finfish aquaculture with special references to reproduction” (acronym: InnovaFish), Operational Programme Sustainable Development of the Fisheries Sector and Coastal Fishing Areas 2007-2013" (OR14-61724-OR1400003/09/10/11). Presented at AQUA 2012 – Prague, 01-05 OCTOBER 2012