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ผู้เขียน หัวข้อ: Is growth retardation present in Nile tilapia Oreochromis niloticus cultured  (อ่าน 1797 ครั้ง)
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« เมื่อ: กุมภาพันธ์ 21, 2010, 02:41:46 AM »

Is growth retardation present in Nile tilapia Oreochromis niloticus cultured in low water exchange recirculating aquaculture systems?

Catarina I.M. Martins ⁎, Daniel Ochola, Stephan S.W. Ende, Ep H. Eding, Johan A.J. Verreth
Aquaculture and Fisheries Group, Wageningen University, P.O. Box 338, 6700 AH, Wageningen, The Netherlands

Aquaculture 298 (2009) 43–50

Keywords:
Growth retardation
Nile tilapia
Size category
Feeding motivation
Stress response
Single-sludge denitrification reactor
Nitrogen

a b s t r a c t

It has been suggested that fish cultured in recirculating aquaculture systems (RAS) growless as compared with fish cultured in flow-through systems due to the accumulation of substances. In the Netherlands, the commercial culture of Nile tilapia Oreochromis niloticus in 300 and 600 MT's systems is done exclusively in RAS operated at waterexchange rates as lowas 30 L/kg feed/day due to nitrate control by single-sludge denitrification reactors. The use of such nearly closed RAS raises the question whether growth retardation (GR) is present in Nile tilapia. This study is the first to investigate the existence of growth retardation in Nile tilapia by comparing the growth, feeding behaviour and stress response ofNile tilapia cultured inRASwith different levels of substances accumulated. Three RAS, operated at 30 L/kg feed/day (HIGH accumulation), 70 L/kg feed/day (MIDDLE accumulation) and 1500 L/kg feed/day (LOWaccumulation) were used. Each RAS contained 24 glass aquaria with individually housed fish. To determine whether GR is size-dependent, per RAS 3 fish size categories were tested in the 57 day experimental period: large (288.7±34.2 g; N=8), medium (162.4±23.4 g; N=8) and small (81.4±21.0 g; N=8). Experimental fish were fed ad libitum, twice per day. Feeding behaviour was determined once per week and wasmeasured as the time taken by each fish to eat the first pellet (latency, LAT) and the total time spent feeding (total feeding time, TFT). Temperature, pH, conductivity, alkalinity, dissolved oxygen, dissolved CO2, nitrogen compounds (TAN,NO2-NandNO3-N), chemical oxygen demand and orthophosphate-Pweremeasured over time. At day 57 fish were weighed, blood sampled and returned to their tanks for an extra experimental period of 15 days, and subjected at day 72 to an acute stress followed by blood sampling. Bloodwas analysed for glucose and cortisol. Results showed that the water quality parameters measured in the 3 RAS (with the exception of alkalinity)were stillwithin the optimumrange for growth of Nile tilapia. Large individuals showed a tendency to growmore in the
LOWtreatment (2.66±1.35 g/kg0.8/day) as compared with the MIDDLE treatment (0.93±1.63 g/kg0.8/day). On the contrary, small individuals grew significantly less in the LOW treatment (3.60±1.74 g/kg0.8/day) as compared with the HIGH (7.22±1.58 g/kg0.8/day) and MIDDLE (6.82±4.54 g/kg0.8/day) treatments. Small fish were more motivated to eat (lower latency) in the MIDDLE (4.63±5.24 min) as compared with the LOW treatment (8.94±6.41 min). In the HIGH accumulation treatment higher glucose levels were observed in the small fish, before and after acute stress, as compared with the LOWaccumulation treatment. In conclusion, this study showed that the extent towhich the accumulation of substances inRAS affects growth depends on fish size: large individuals show a trend towards growth retardation in the highest accumulation RAS while small individuals, on the contrary, seem to grow better in such systems.
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