This study investigated the impact of different nitrogen sources on the growth and biochemical composition of two diatom species, Chaetoceros calcitrans and Thalassiosira weissflogii, and evaluated their use as live feed for Litopenaeus vannamei larvae. Diatoms were cultured in a Conway medium supplemented with four nitrogen sources: potassium nitrate (control), urea, ammonium sulfate, and ammonium nitrate. In a separate experiment, white-leg shrimp larvae (300 larvae/L) at stage Nauplius 6 were fed diets consisting of C. calcitrans, T. weissflogii, or a combination of both diatoms under controlled conditions. The results indicated that urea, ammonium nitrate, and ammonium sulfate significantly enhanced the growth and nutrient composition of C. calcitrans and T. weissflogii compared to the control (potassium nitrate). In C. calcitrans, ammonium nitrate significantly increased protein and lipid contents, while carbohydrate levels were the highest in the control. Similarly, urea and ammonium sulfate treatments yielded the highest lipid levels, whereas the control exhibited the lowest. For T. weissflogii, the control achieved the highest cell count on day 4, but ammonium nitrate significantly improved protein and lipid contents while reducing carbohydrate levels. A mixed diet of C. calcitrans and T. weissflogii significantly enhanced growth performance and reduced mortality rates in L. vannamei larvae compared to single-species diets. In conclusion, the findings indicated that ammonium nitrate was an efficient nitrogen source for enhancing diatom growth. Additionally, combining C. calcitrans and T. weissflogii as a diet improved growth and survival of L. vannamei larvae, offering practical implications for aquaculture.

The cyanobacterium Spirulina platensis is quite spread all over the world due to its high nutritional value. It has been used as a protein source and vitamin supplement in healthy diet, in aquaculture and fisheries. Cyanobacterium Spirulina is capable to grow in various kinds of culture media. Furthermore, decomposed organic and inorganic nutrients media have been proven to be a good source of culture medium for Spirulina by many researchers. In this work, S. platensis was cultivated using dry vermicompost from fish sludge (VCFS) or cow manure (VCCM). 100 g of dry vermicompost from each source (VCFS/VCCM) collected and compared with Aiba and Ogawa liquid medium which was used as a culture medium. The results obtained showed that the highest protein and "chlorophyll a" ratio of S. platensis were observed in the biomass harvested from T2 (VCCM) and T3 (Aiba and Ogawa liquid medium). The highest dried S. platensis biomass was harvested from T2 (VCCM) while the lowest came from T1 (VCFS). The chemical composition ( as % of dry weight) revealed that (VCCM) was higher in total phosphorus, total nitrogen and organic matter than (VCFS).

The present study was conducted to evaluate the individual and combined effects of dietary crude protein levels and magnetic water treatment on the growth performance, water quality, body composition, physiological responses, and immunity of Oreochromis niloticus. Using a 3 × 2 factorial design, three levels of dietary crude protein (25%, 30%, and 35%) and two water types (magnetized and non-magnetized) were tested. A total of 180 juvenile tilapia (average initial weight: 4.13 ± 0.004 g) were randomly assigned to six treatment groups and reared for 10 weeks. Results showed that magnetic water treatment significantly improved dissolved oxygen and pH, while reducing ammonia, nitrite, and nitrate concentrations. Growth performance indicators, including final weight, specific growth rate, feed conversion ratio, and average daily gain, were significantly improved by both magnetic water and increased dietary protein. Carcass crude protein content improved with both the higher dietary protein level and magnetic water, while lipid content decreased. Liver and kidney function indicators (AST, ALT, ALP, and urea) were significantly improved by magnetic treatment and higher protein levels. Blood biochemical markers (TP, ALB, and GLO) were elevated, while glucose, cholesterol, and triglycerides were reduced by magnetic water; significant interactions were observed for globulin, triglycerides, and total protein. Antioxidant enzyme activities (SOD, CAT, and GPx) increased, and MDA decreased in response to magnetic water and high-protein diets. Similarly, digestive enzyme activities (lipase, protease, and amylase) and immune parameters (IgM and lysozyme) were significantly improved, with the best values recorded in the 35% protein + magnetic water group. In conclusion, magnetic water treatment and dietary protein level independently and interactively affect the physiological performance and health of Nile tilapia, with the best outcomes obtained at 35% protein under magnetic water conditions.

The present study was carried out to assess the effects of Spirulina platensis as a feed additive to enhance color and immunity of goldfish (C. auratus). Fish (3.5 g) were randomly assigned to eight concrete ponds (8 m3) with three fish / m3 capacity, and they were split into four treatments in two replicates. A commercial diet of 30 % crude protein was fed to fish in the four treatments as follow: the control group received no additive of Spirulina platensis, T1, T2 and T3 received 6, 8 and 10 g S. platensis per kg, respectively. The highest total carotenoids concentration in the skin of C. auratus was in T2 (1.32 ± 0.15 μg g-1). While MDA exhibited a considerable decline, antioxidants SOD, CAT, and GPx showed tremendous increases. At the termination of the feeding study, there was no discernible difference between the control and the investigated treatments concerning lysozyme activity, IGM, ALT, AST, and ALP. This discrepancy might be connected to spirulina's capability to improve fish health. Histological studies support these results, as no negative changes occurred in the cellular composition of liver tissue. Therefore, we conclude that using Spirulina platensis at a rate of 8 g / kg of feed improves the color quality of goldfish and thus increases their price.