Obtaining and maintaining a healthy, productive aquaponic system requires intensive scienti ic research, monitoring and also adjustments, when necessary. To quantify the nitrogen budget for a stellate sturgeon-spinach integrated LECA grow bed aquaponic system, where three plants densities were used. The experiment was made in triplicate, using a 12 aquaponic units LECA grow bed aquaponic system. Three crops densities were used (V1-59crops/m 2 , V2-48crops/m 2 and V3-39crops/m 2 and V4-no crops, only with LECA grow bed). Fish were were fed with 41% brute protein feed, at an average feeding ratio of 1.75% of total biomass. Water samples were taken and analysed by using photometric methods (Merck kits). The stellate sturgeon meat, spinach and also faeces nitrogen content was determined by Kjeldahl method. Differences between the removal rates for each of the three variants of tested crops densities were signi icant higher (p<0.05) at V1 compared to V3 and also higher at all three variants comparing them to the control variant. The amount of ammonium removal rates from bio ilter and LECA grow bed was signi icant (p<0.05). Also, differences between spinach nitrogen composition from V3 compared to V1 were found signi icant higher (p<0.05). The nitrogen content from ish meat and ish faeces was found to be within normal limits, appear also in the literature. Considering the nitrite and nitrate concentrations, only spinach grown in aquaponic conditions, as presented above, at densities of 59crops/m 2 , is marketable. In addition, it can be concluded that spinach growth in LECA grow bed aquaponic systems have a higher nitrogen content, comparing with the one growth using loating rafts technique.

The importance of water for life, as a component of the global ecosystem, is becoming clearer and clearer. Water resources are influenced by many activities such as those belonging to agriculture and industry as well as domestic activities. This paper has contributed to the modeling aquaculture business domain and to improve some of quality indicators of the Danube's corps of water. The aims of this study is to integrate in aquaculture business model the aquaculture production system with agricultural production system (aquaponics) and to reconcile and achieve social, economic and environmental objectives with processing and marketing action to add more value to end aquaponics products.

The purpose of this research was to determine the effect of some phytobiotics on biochemical composition of Nile tilapia muscle tissue reared in a recirculating aquaculture system. The experiment was conducted for fourteen weeks, from August 17 to November 27, 2012. The experimental variants were: V1-control, V2-1% Rosmarinus officinalis/kg feed; V3-1% Hippophae rhamnoides/kg feed and V4-1% Zingiber officinale/kg feed. During the experiment, the sampling for biochemical analysis of muscle tissue was performed at the beginning of the experiment (17.08.2012), on intermediary moment (28.09.2012) and at the end of the experiment (27.11.2012), from fresh meat. The results showed significant differences (p<0.05) both between initial (Vi) and intermediary (Vint-28.09.2012) moment and between experimental variants (Vint) in terms of protein, fat, moisture and dry matter percentage. At the end of the experiment were registered significant differences (p<0.05) with respect to protein and moisture percentage. Also, in this paper is presented the dinamics of nutrient retention efficiency (PER-g/g, PUE-%, RP-g/fish and RL-g/fish) at Nile tilapia, in the muscle tissue. At the intermediary moment, in V3 was registered the lowest value of fat content (1.22%), and in V4 the highest value of protein content (13.11%). In conclusion, rosemary, sea buckthorn and ginger, in concentration of 1%/kg feed, influenced significantly the biochemical composition of muscle tissue at Oreochromis niloticus species.

Integrated aquaponic systems represent a viable solution for the continuing upward trend of humanity demands, as long as the balance between productivity and inal products quality and biosecurity is found. To identify the quality, in terms of nitrite and nitrate concentrations, of both spinach and stellate sturgeon meat, obtained under different culture densities (spinach) and feeding regimes (stellate sturgeon), in an integrated aquaponic system. The experiment on spinach was made in triplicate, by using 3 stocking densities: (V1-59crops/ m 2 , V2-48crops/m 2 and V3-39crops/m 2). A 9 media grow bed hydroponic modules (LECA) and a 4 ish rearing units RAS were integrated, forming the integrated aquaponic experimental system. Fish were divided in 4 groups and were fed with 41% brute protein feed, at the following rations: F1-2.21%; F2-1.85%; F3-1.64% and F4-1.28% of total biomass. Chemical analyses concerning nitrite and nitrate levels were made on 5 samples, by using Griess method-STAS 9065:2002. A statistical signi icant difference (p<0.05) was recorded between V1 and V3, in terms of both nitrates and nitrites concentrations. Also, higher nitrite and nitrate concentrations were observed on spinach grown under aquaponic conditions, comparing with spinach derived from ield culture. Differences between F1 and F3, F4 nitrite and nitrate concentrations we observed to be signi icant (p<0.05). Considering the nitrite and nitrate concentrations, spinach grown in aquaponic conditions, as presented above, at densities of 59crops/m 2 and 48crops/m 2 , is marketable. Also, the level of ish meat nitrites and nitrates, from all 4 experimental variants, did not exceed the safety limits for human consumption.

The present paper contributes to the modeling aquaculture. The