Despite wide studies of biomonitoring aquatic environment through dynamics of host–parasite interaction, bio-indicators to track the influence and accumulation of heavy metals on fish are still few. The present study sheds light on the relation between fish parasites and heavy metals as it threatens fish’s health and, as a consequence, that of humans after fish consumption. Samples of Nile tilapia (Oreochromis niloticus) were collected in Burullus Lake, a wild fish source, and from a private fish farm in Kafr El-Sheikh Governorate, in Egypt. They were exposed to various pollutants associated with anthropogenic activities to determine the levels of accumulation of Fe, Zn, and Cu, along with the top three most toxic metals (As, Cd, and Pb) in water and fish tissues of gills, intestine, liver, and muscles in both wild and farmed O. niloticus. The results showed the order of abundance: Fe < Zn < Pb < Cu < As < Cd. In waters of both farmed and wild fish, there was a significant negative relation between parasite prevalence and heavy metals, including Zn, Pb, and As. Also, there was a significant positive relation between parasite prevalence with Cu while no significant relation was found with Fe and Cd. Heavy metal content was significantly higher (p > 0.05) in non-infected than infected farmed and wild O. niloticus. In addition, a significantly decreased concentration (p > 0.05) of essential heavy metal was recorded in wild fish compared to farmed specimens, while non-essential heavy metal was significantly higher (p > 0.05) in wild compared to farmed fish. Bioaccumulation factors (BAF) of different organs of O. niloticus were ranked in ascending order: Liver > Gills > Intestine > Muscles. In general, the risk assessment showed safe human consumption of farmed and wild fish under the reported environmental conditions in this study. Moreover, the parasite's presence can be adopted as a surrogate indicator to estimate the potential impact of heavy metal pollution and accumulation.

The study aimed to determine the effects of wet salting, dry salting, and smoking processing methods on the heavy metal and mineral concentrations in the cultivated fish species which collected from private fish farms at Kafr El-Sheikh Governorate, Egypt, during winter, 2017. The impacts of fish processing on mineral contents of the raw and processed fish were significantly different (P ≤ 0.05). The maximum level of metals in the raw and processed fish samples (wet salted, dry salted, and smoked fish) were recorded for iron ion and the minimum level determined for cadmium ion. However, the highest sequences of the minerals in the raw and processed samples were obtained in this order Na > K > P > Ca. Regarding to processing methods, significant decreases occurred in the minerals of Ca, K, and P, but smaller decrease in the heavy metals of Cd, Cu, Fe, Mg, Ni, and Zn in the wet salted grass carp. In the dry salted mullet, the changes in the minerals and heavy metals are relatively small. However, the greatest changes are on smoked grass carp; most of the minerals, including Ca, K and P, except Na, significantly increased. In heavy metals, Cu, Fe, and Zn, except Mg and Ni, also significant increased.

The present study assessed the effect of hot smoke at 50-90°C for 5-6 h using hard sawdust of beech wood and two salt levels (10% and 16%) on keeping quality of grass carp, Ctenopharyngodon idella, fillets stored at 4±1°C. Chemical composition, physiochemical aspects, minerals and sensory analysis were determined. Results showed that, the mean values of moisture,

Medicinal plants are a potential safe source of bioactive compounds. Fish diet supplemented with the medicinal plant bottle gourd (Lagenaria siceraria) seed powder was evaluated in this study for the potential effect on growth performance, antioxidative status, immunological response, and resistance to infectious pathogens in the Nile tilapia (Oreochromis niloticus). Nile tilapia fingerlings with mean weight ( ± SD)= (25.64 ± 0.17 g), were fed four L. siceraria seed supplemented diets (LSSD) at 0.0, 1, 2, and 3% for 60 days. Specimens were then challenged with the bacterium Aeromonas hydrophila for 10 days. Also, three different concentrations (2.5, 5, and 10 ml/L) of Lagenaria siceraria ethanolic extract (LSEE) were tested for their antibacterial and antiparasitic efficacy on four selected bacterial and one parasitic species. All parameters’ values generally improved with elevating the content of the L. siceraria seed powder in the diet. Dietary administration of LSSD-3% enabled significant (P < 0.05) higher growth performance, and feed utilization efficiency. It reduced the mortality induced by A. hydrophila infection, increased crude protein content in the fish body and exhibited the highest in vitro antibacterial and antiparasitic efficiency. RBCs, WBCs, Hb, PCV, MCV, MCH, and total serum protein values in pre- and post-challenge groups were significantly higher (P < 0.05) in the LSSD-3% group. While MCHC, ALT, AST and glucose levels were significantly lower (P < 0.05) than those of the other groups. Lysozyme and antioxidant enzyme activities in pre- and post-challenge groups were also higher (P < 0.05) in the LSSD-3% group compared to the other groups. LSEE provided good efficacy against Gram-negative bacterial strains, mild efficacy against Gram-positive bacterial strains, and an antagonistic effect on the parasite Cichlidogyrus Tilapiae. The 10 ml/L concentration was the most effective against the pathogens followed by the 5 ml/L concentration and then 2.5 ml/L. Our findings suggest the feasibility of supplementation of Nile tilapia (O. niloticus) diet with L. siceraria seed powder by 3% to improve the growth performance, immunity, and vital parameters.

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