The present study aims to investigate the influence of zeolite usage and stocking densities on various parameters, including ammonia removal from water, accumulation of heavy metals in fish organs, water quality, growth performance, feed efficiency, muscle composition, as well as hematological and biochemical parameters in European seabass (Dicentrarchus labrax) over a 90-day duration. A total of 2400 D. labrax with an initial weight of 9.83 ± 2.02 g and initial length of 9.37 ± 0.32 cm were distributed among 24 tanks. The research involved six distinct treatment groups, with two different zeolite levels (0 and 15 ppt) and three stocking density levels (50, 100, and 150 fish/m³), each replicated four times. The results of the research demonstrate a statistically significant improvement (p < 0.05) in water quality measures with the introduction of zeolite. The successful implementation of this amendment mitigated the adverse effects of fish density on water quality parameters. Higher stocking density negatively impacted European sea bass growth, feed utilization, and hemato-biochemical indicators. Zeolite use effectively alleviated these adverse effects, particularly on performance, feed utilization, hematological, and biochemical parameters. The study’s results indicate that the utilization of zeolite has shown to be efficacious in mitigating the accumulation of heavy metals in both water and fish organs, while concurrently augmenting fish attributes. However, the increase in density led to a significant decrease in the accumulation of heavy metals in both water and fish organs. The present study highlights the capacity of natural zeolites to mitigate the negative consequences associated with water quality concerns. The efficiency of these zeolites in limiting the accessibility of heavy metals in polluted water is shown, hence minimizing their accumulation in fish organs. In addition, the improvement of fish performance has the capacity to have a beneficial influence on both the well-being and efficiency of fish in aquaculture. Additional research is essential to fully understand the complex molecular pathways involved in utilizing natural zeolite under different fish densities.

Water exchange rates were manipulated to reduce the negative effect of high stocking density adversely affects the rearing condition such as water exchange rates has to be manipulated to elevate stress factors. European sea bass juveniles with an average body weight of 4.5 g fish/m3 were stocked at three densities (50, 100 and 150 fish/m3)in 12 concrete ponds. Two water exchange rates (20% and 30% of total water volume) were applied for 18 weeks to investigate their influence on reducing the negative effect of stocking density and enhancing the water quality. The results indicated that the 30% water exchange rate was better for achieving high growth performance and feed utilization, regardless of stocking density. Water quality (total ammonia nitrogen, un-ionized ammonia, nitrite and nitrate) was enhanced, dissolved oxygen increased and all harmful nitrogen derivatives decreased when the 30% water exchange rate was applied. Additionally, the 30% water exchange rate significantly increased the water temperature (16.33°C) compared to the 20% exchange rate (14.33°C), and the final body weight, weight gain and specific growth rate were significantly increased (P<0.05) with the 30% water exchange rate. The survival rate was 97%, which was significantly the highest at the density of 50 fingerlings/m3 at a water exchange rate of 30%. Although the feed conversion ratio, protein efficiency ratio, and protein productive value significantly improved with the 30% water exchange rate at all densities, the 100 fish/m3 stocking density achieved the best feed conversion ratio. However, the haematological parameters showed a significant increase (P<0.05) in haemoglobin, haematocrit, white blood cells, lymphocytes, monocytes and neutrophils with a low stocking density and a 30% water exchange rate.

Aquaculture output, sustainability, and profitability can be enhanced by using functional feed additives. The effect of supplementation with two different dietary levels of propylene glycol (PG) and essential oils (EOs) was evaluated in Nile tilapia. A total of 150 juvenile fish were randomly allocated into five groups. Growth performance, feed utilization, serum biochemistry, hematology, and gene expression were assessed. PG supplementation significantly improved growth performance, feed conversion, protein efficiency, and energy utilization. Both additives significantly reduced cortisol and glucose levels and altered liver enzymes and lipid profiles. PG improved immunological indices, while hematological responses were dose-dependent; both EOs and PG increased hematocrit, mean corpuscular volume (MCV), and mean corpuscular hemoglobin (MCH). Moreover, the high PG dose significantly increased platelet counts, reduced hemoglobin (Hb), and elevated hematocrit. Additionally, EOs significantly upregulated antifreeze protein IV (AFPIV) and fat metabolism-related genes in a dose-dependent manner, indicating a potential role in lipid mobilization and stress tolerance. Expression analysis of the immunoglobulin H (IGMH) gene revealed a significant increase in PG-supplemented groups, suggesting its immunostimulatory potential. Overall, PG enhanced immunity and growth performance, while EOs promoted AFPIV and fat metabolism gene expression. Therefore, PG and EO supplementation could serve as an effective functional strategy to enhance O. niloticus growth, stress adaptation, and immune resilience.

This study evaluated the viability of using groundwater (GW) compared to seawater (SW) in European sea bass (Dicentrarchus labrax) aquaculture. Wild broodstock were captured 2 months before spawning and acclimated to tanks with either SW or GW 1 week prior. Females received HCG injections in both water types. Fertilized eggs were collected into six conical tanks supplied with SW or GW. At 7 days post-hatch (dph), larvae were transferred to 12 rearing tanks with SW or GW, using either flow-through or static water systems (three replicates per treatment). Growth performance and survival were monitored up to 60 dph. The results revealed that spawning induction of European sea bass broodstock failed in GW while succeeded with egg fertilization and hatchability up to 97 ± 1% in SW. Hatching was 96 ± 1% for the fertilized eggs transferred from SW to GW incubators. However, the newly hatched larvae suffered high mortality up to 7 dph, which gradually decreased with the start of exogenous feeding. During the period from 7 to 60 dph, larvae and post-larvae showed normal viability and survival with either flow-through or static water systems in SW and GW. At the end of the experiment, the results indicated that water sources in combination with the water-rearing systems significantly affected post-larvae performance. Larval survival was significantly higher in both GW systems (static: 88.8 ± 2.1%, flow-through: 89.9 ± 5.6%) and in the static SW system (84.15 ± 2.8%) compared to the flow-through SW system (70.4 ± 5.8%). Moreover, the final length of larvae at 60 dph was significantly higher in the static GW system (2.27 ± 0.09 cm). In addition, larvae reared in static GW had higher final weight (140. 00 ± 4.24 mg). Total protein and total lipid contents were significantly higher in larvae reared in GW than those reared in SW for both water systems. The study suggested a static GW system for European sea bass larval rearing starting from 7th dph onwards to achieve better larval quality and higher survival. Future research is needed to enhance GW with new technologies to accommodate D. labrax–induced spawning and newly hatched larval rearing.