A feeding trial was conducted to evaluate the effect of nucleotides supplementation to low‐fish meal feed on growth and fatty acid composition of rainbow trout. Six isonitrogenous (42% crude protein) and isolipidic (18% crude lipid) diets were formulated containing fish meal and plant ingredients as main protein sources. The control diet was a basal diet without supplementation of nucleotides, and five experimental diets were prepared by supplementing one of the five different nucleotides in the form of 5′‐monophosphate (0.15%), that is inosine (IMP), adenosine (AMP), guanosine (GMP), uridine (UMP) and cytidine (CMP) onto basal diet. Two hundred forty juvenile rainbow trout with an initial average body weight 9.8 g were randomly distributed into twelve aquaria. After 15 weeks of feeding period, growth performance and feed utilization of rainbow trout were not significantly different among dietary treatments. Dietary GMP, UMP and CMP tended to accumulate crude lipid in the muscle and whole fish body. Moreover, dietary GMP, UMP and CMP significantly increased hepatic 18:3n‐3 and long‐chain homologue 18:4n‐3 and 20:4n‐3 contents. Hepatic 18:2n‐6 content showed also increase in fish fed GMP, UMP and CMP diets, but decreased in long‐chain homologue 20:3n‐6 and 20:4n‐6 contents. Decrease in 20:4n‐6, 20:5n‐3 and 22:6n‐3 contents was also found in the muscle of fish fed IMP, GMP and CMP diets. The present study clearly showed that there was no positive effect of dietary nucleotides on growth of fish, but dietary nucleotides particularly GMP, UMP and CMP altered polyunsaturated fatty acid composition of rainbow trout.

Oxygen is a vital parameter in aquaculture activities. The decrease of dissolved oxygen levels in aquaculture media should be highly observed, since very low dissolved oxygen conditions (hypoxia) could negatively affect to the growth and survival of fish. Therefore, research on the condition of hypoxia is very important to be studied. This study was conducted in January-February 2013 at the Laboratorium of Fish Reproductive Physiology, Pukyong National University, South Korea to measure oxygen consumption in tilapia Oreochromis niloticus (total length: 14.2 ± 1.4 cm, weight: 31.3 ± 2.0 g) under normal conditions (normoxia) and hypoxia. Measurement was conducted using respirometer (dimension: 20 × 17,5 × 10 cm; volume: 3,5 L) every 10 minutes during four hours of observation. Experiment was conducted with three replications. The results showed that oxygen consumption of tilapia fingerlings in hypoxia conditions (12.09 ± 3.20 mg O2/kg/h) was lower than normoxia (35.67 ± 4.19 mg O2/kg/h) (P<0.01). Continuous hypoxic conditions could negatively affect fish movements, which could ultimately lead to mortality when dissolved oxygen levels are very low. Meanwhile, the results on determination of critical oxygen levels for tilapia showed a dissolved oxygen range of 1.9 ± 0.5 mg/L

The present study investigated interactive effect of different levels of dietary fish oil and pyrimidine nucleotide supplementation on growth and fatty acid composition of juvenile rainbow trout. Six experimental diets were formulated with two different levels of fish oil. High fish oil (HFO) diet contains 120 g/kg fish oil, while low fish oil (LFO) diet contains 40, 60 and 20 g/kg fish, linseed and rapeseed oils respectively. Uridine 5'-monophosphate (UMP) or cytidine 5'-monophosphate (CMP) disodium salt was supplemented onto each diet at 1.5 g/kg respectively. For control diet, UMP and CMP were not supplemented to HFO and LFO diets respectively (HFO-Cont. and LFO-Cont.). Rainbow trout with initial average body weight of 13.5 g were randomly placed into 12 tanks and offered one of the six diets for 12 weeks. Growth, feed utilization and hepatosomatic index (HSI) of fish were not influenced by either fish oil or pyrimidine nucleotide supplementation. This trend was also similar on the crude lipid content in the liver and proximate composition in the muscle and whole fish body. In addition, fatty acid composition in the liver was influenced by fish oil level, but not by pyrimidine nucleotide supplementation. Interestingly, pyrimidine nucleotide supplementation affected 20:4n-6 and 22:6n-3 contents in the muscle of fish. In summary, although dietary UMP and CMP have no positive effect on growth, it affected on the fatty acid composition of fish by increasing muscular 20:4n-6 and 22:6n-3 contents particularly when it is supplemented in low fish oil-based diet. K E Y W O R D Scytidine 5'-monophosphate, fish oil, lipid, long-chain-polyunsaturated fatty acid, uridine 5'-monophosphate How to cite this article: Ridwanudin A, Kasuya H, Haga Y, Kabeya N, Satoh S. Interactive effect of dietary fish oil and pyrimidine nucleotide supplementation on the fatty acid composition of juvenile rainbow trout Oncorhynchus mykiss: Enhancement of ARA and DHA contents in the fillet of fish fed-supplemented diet.