St. Stoyanova*, Y.Staykov, G. Zelqzkov, I. Sirakov, G.Nikolov
Department of Biology and Aquaculture, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria (Manuscript received 26 October 2016; accepted for publication 22 November 2016)
Abstract. The rainbow trout (Oncorhynchus mykiss), an important species in Bulgarian aquaculture, is farmed in different production systems as raceways, net cages etc. The aim of the present study was to evaluate the effect of two different rearing systems on fish production, survival rate, meat chemical, mineral composition and farming economic efficiency of culticated rainbow trout (Oncorhynchus mykiss). The information from a survey on fish production and economic efficiency traits was collected from two national rainbow trout farms using the two commonest fish farming systems: in raceways, Happy Fish Ltd fish farmandinnetcages,ForestGroupLtdfishfarm.Theaverageindividualweightgain(g),totalweightgain(kg), feedconversionratio,productioncostsof1kg fish and the economic efficiency coefficients were determined for the two studied fish farms. The final live weight of rainbow trout in net cages was 0.30 kg vs 0.35 kg in raceways. The average individual weight gain was higher in raceways farming system (0.30 kg) than in net cages farm (0.26 kg). The mortality rate of fish in raceways was considerably lower: only 1% as compared to that in net cages (4%). The feed conversion ratio at the end of the experiment showed identical values for trout in both farms 1.01. The meat water content of fish reared in raceways and net cages was 77.46±0.65% and 74.52±0.52% respectively (P≤0.01).The protein content of fish meat was higher in fish farmed in net cages 18.84±0.29% as compared to fish cultivated in raceways 17.60±0.49% (P≤ 0.05). Meat fat content of rainbow trout, reared in the net cage system was also considerably higher (5.26±0.30%) than the respective parameter in fish farmed in ponds(3.60±0.15%)(P≤0.001).The content of Ca and P washig her in rainbow trout sreared in race ways(138.96±1.12mg.kg-1and2844.32±39.31mg.kg- 1) compared with the values of these parameters of fish in net cages (134.46±1.96 mg.kg-1 and 2690.31±42.81 mg.kg-1) (P≤ 0.05). The K and Na content exhibited the opposite tendency with substantially higher values in trouts farmed in net cages (2658.26±48.75 mg.kg-1 and 671.31±16.16 mg.kg-1) than in fish in raceways (2552.90±39.93 mg.kg-1 and 569.32±13.75 mg.kg-1)(P≤0.05, P≤0.001). The production costs of 1 kg rainbow trout were by 17.27% lower in the Forest Group farm than in the Happy Fish farm. The coefficient of economic efficiency in the net cage farm was by 23.44%higher than that of the race ways production system.