GROWTH DYNAMICS OF RAINBOW TROUT (ONCORHYNCHUS MYKISS) FROM FIAD-TELCISOR SALMONID COMPLEX, BISTRITA-NASAUD COUNTY.

Growth dynamics of rainbow trout (Oncorhynchus mykiss), superior to other salmonids species, led to the exploitation of this species in the most countries of the world. The individuals of this species, depend on many factors, like environment, nutrition and genetics. In this study, authors have followed over 540 days, the evolution of body mass and average daily gain at the specimens of rainbow trout from Fiad-Telcisor salmonids complex, Bistrita-Nasaud county, from the larval stage and up to the stage of trout for consumption with an average weight of 250 gr. These studies are necessary to prepare a strategy on fisheries production planning, depending on market demand of these products and eliminating additional costs due to over production. Fish and fish products always represented a staple food in human nutrition. The aquatic resources of continental and oceanic natural waters, have permanently assured the humanity's food needs, but today, on the conditions of the demographic boom, may be destroyed the ecosystems balance, on the strenght of irrational exploitation of their (Svennevig & co., 2000). For this reason, specialists' attention bound for aquaculture, field of the last years a real progress (Goldburg & Naylor, 2005). On this economic stage, a fierce commercial competition and significantly reduction of the market price, involving development and alignment a new concept of strategy, to decrease the production price. For this, aquaculture producers focus their efforts to obtain high yields at a high quality level and in conditions of maximum efficiency. A common situation on the fish market in Romania, is to sell products. Lack of strategy on the relationship between production capacity of fish farms and marketing opportunities of these products, lead to the accumulation of hardly marketable stocks which involving additional financial burden (Popescu, 2009). To avoid such situations, are requested market studies and research on the possibilities to obtain rhytmic and constant productions. They involve serious knowledge about factors which influence the physiology of fish growth (Cocan & co., 2009). In Romania, but also in many other countries around the world, salmonid species predominantly found in farms are rainbow trouts (Oncorhynchus mykiss). It is successfully exploited, due to its plasticity and resistance to changes in environmental conditions and diseases, and due to efficient conversion of feed (Cocan, 2008). There have been numerous studies on the factors that influence the growth of rainbow trout, including: growth density, environmental conditions, water quality, the rate of removal of water or operating system adopted (North & co., 2006; Roque d'Orbcastel & co., 2009; Sørensen & co., 2005; Matthews & co., 1997; Clark, 2003). Leatherland (1993), has conducted studies on interaction between plasma growth hormone, thyroid hormones and cortisol concentrations in rainbow trout, depending on the density of growth (150 kg/m³, respectively 60 kg/m³). The results demonstrated that to a high density, the growth rate drops significantly, due to high concentration of cortisol, but also due to restricted diet because of the high density. Because are poikilotherms, trouts shows changes of behavior and some physiological parameters according to season (Gallardo, 1997). Temperature is one of the abiotic factors with a major influence on the development of metabolic processes. Farming system adopted are also greatly influence on the growth dynamics of rainbow trout, each showing the advantages and disadvantages. Recirculating systems (RAS) providing optimal growth conditions, medial parameters being monitored continuously (Sirakov & Ivancheva, 2008), but inefficient water filtration systems can affect meat quality (Rønsholdt & McLean, 1999), or may give rise to health problems (Svobodova & co., 2005). Classical breeding systems are often at risk of contamination by polluted waters (Moogonei & co., 2010), and environmental conditions can not be controlled. In this study, authors have monitored the growth dynamics, body mass evolution and average daily growth of rainbow trout (Oncorhynchus mykiss), from Fiad-Telci or salmond complex. [ABSTRACT FROM AUTHOR]