This study tested the hypothesis that different diets could modulate mercury (Hg) trophic transfer by concurrently altering the transfer of energy (in terms of growth) and transfer of Hg (in terms of biodynamic process). Firstly, we conducted a 40-d laboratory bioaccumulation experiment, in which tilapia (Oreochromis niloticus) was exposed to inorganic mercury (Hg[II]) and methylmercury (MeHg) via feeding on three distinct diets (macrophyte, freshwater shrimp, and commercial pellets) at a fixed ingestion rate of 0.065 g g⁻¹ d⁻¹. During the dietary exposure period, tilapia exhibited Hg species- and diet-dependent Hg trophic transfer patterns and diet-specific growth rates. We then employed a biokinetic model to assess how diet-specific biodynamics and/or diet-specific growth rates modulated the overall Hg bioaccumulation and trophic transfer. The diet-specific assimilation efficiencies (AEs) were monitored using radioisotope technique, and the determined AEs of Hg(II) (8.6%–29.7%) varied by 3.5 times among diets whereas the MeHg AEs (94.4%–97.1%) were not affected. The biokinetic modeling further revealed that Hg(II) trophic transfer in tilapia was controlled by the diet-specific AEs, while MeHg trophic transfer was governed by the diet-specific growth rates. Specifically, a diet-derived high growth rate reduced the MeHg trophic transfer in pellets-fed tilapia, and the overall accumulated MeHg level in fish was under the control of both somatic growth dilution and dietary MeHg influx. Moreover, we observed that the Hg levels (mainly as MeHg) in fast-growing farmed tilapia were significantly lower than wild-living tilapia after 100 d exposure in the field, attributed to somatic growth dilution (SGD). Both the laboratory and field study therefore demonstrated the importance of diet-derived SGD in modulating mercury trophic transfer in aquatic food webs.

Aquaculture impacts on aquatic organic matter and ecosystem integrity are poorly understood, especially in tropical regions. Here, we investigated the impacts of Nile tilapia net cage farming on the elemental stoichiometry, fluorescence components, and stable isotopes of dissolved organic matter (DOM) of the large, tropical Furnas Reservoir (SE Brazil). Early-stage fish farming, i.e., relatively small and recently implemented farms, had detectable incipient effects on DOM characteristics, and these effects differed between reservoir branches. In the less eutrophic Rio Grande branch of the reservoir, we found a reduction in natural humic-like DOM components and an increase in a protein-like DOM component as far as 100 m away from fish farms. Further, we observed a decrease in δ¹⁵N-TDN due to fish farming. In the more eutrophic Rio Sapucaí branch, there were only local decreases in C:N ratios, as well as rises in C:P and N:P of DOM due to fish farming. These results suggest that early-stage fish farming had local but detectable effects on aquatic DOM that depended on previous eutrophication levels and highlight the need to assess the early impacts of fish farming on tropical reservoirs by combining different monitoring strategies.

Two farmed freshwater fish species Nile tilapia (Oreochromis niloticus) and jade perch (Scortum barcoo) were cultured with food waste-based diets and compared with commercial formulated control diet for a period of six months. Sixteen priority polycyclic aromatic hydrocarbons (PAHs) in the diets and cultured fish meat were tested by gas chromatography–mass spectrometry. No significant differences of ∑PAHs were observed between Nile tilapia and jade perch fed with food waste-based diets and control diet (p > 0.05). However, there were significantly higher concentration of ∑PAHs in market fish compared with the same species of fish fed by food waste-based diets (p < 0.05). Thus, the food waste-based diets have a potential to lower the PAH concentrations in farmed fish when compared with market fish. Based on the PAH concentrations, a human health risk assessment was made. The results indicated there were no non-cancer and very low cancer risks of consuming fish cultured with food waste-based diets at the 95th centile (Nile tilapia: hazard index (HI adult) = 0.343 × 10−3, HI children = 0.614 × 10−3 and cancer risk value = 0.943 × 10−6; jade perch: HI adult = 0.456 × 10−3, HI children = 0.814 × 10−3 and cancer risk value = 0.291 × 10−6). In general, the fish fed with food waste-based diets were unlikely to cause adverse health effects, based on the concentrations of PAHs. There is great potential for using food waste-based diets as an alternative to commercial feeds for cultivating freshwater fish.

Aquaculture, also known as aqua farming, is defined as farming fish, crustaceans, mollusks, aquatic plants, algae, and other marine organisms. It includes cultivating fresh- and saltwater populations under controlled conditions compared to commercial fishing or wild fish harvesting. Worldwide, carp, salmon, tilapia, and catfish are the most common fish species used in fish farming in descending order. Disinfectants prevent and/or treat different infections in aquatic animals. The current review indicates the uses of different disinfectants against some important pathogens in aquaculture, with particular reference to tilapia (Oreochromis niloticus) farming. A single review cannot cover all aspects of disinfection throughout aquaculture, so the procedures and principles of disinfection in tilapia farming/aquaculture have been chosen for illustration purposes.

This study aims to determine the maximum concentration and the long-term effects after exposure to a bio-insecticide with active ingredients eugenol and azadirachtin on the survival rate, immunity, and growth of Nile tilapia. The method used in this study was experimental, using a completely randomized design (CRD) with six treatments and three replications. Fishes were exposed to eugenol and azadirachtin at concentrations 10, 20, 30, 40, and 50% of LC50 value for 14 days, followed by 14 days of maintenance to see the effect on growth. The results showed that 66 mg.L-1 treatment was a concentration that did not interfere with the survival rate of Nile tilapia, which was 86.7%. The number of leukocytes increased on the third day by the highest increase in 66 mg.L-1 treatment at 12.01 × 104 cells.mm-3. Meanwhile, erythrocytes decreased, with the highest decrease in 66 mg.L-1 treatment at 1.13 × 106 cells.mm-3. The average growth rate in fish slowed down with increasing concentrations of exposure, with the lowest average growth in length and absolute weight in the 66 mg.L-1 treatment was 0.57 cm and 1.68 g.