Organ-Specific Metabolome Deciphering Cell Pathways to Cope with Mercury in Wild Fish (Golden Grey Mullet Chelon auratus)

Metabolomics is a powerful approach in evaluating the health status of organisms in ecotoxicological studies. However, metabolomics data reflect metabolic variations that are attributable to factors intrinsic to the environment and organism, and it is thus crucial to accurately evaluate the metabolome of the tissue/organ examined when it is exposed to no stressor. The metabolomes of the liver and gills of wild golden grey mullet (Chelon auratus) from a reference area were analyzed and compared by proton nuclear magnetic resonance (1H NMR)-based metabolomics. Both organs were characterized by amino acids, carbohydrates, osmolytes, nucleosides and their derivatives, and miscellaneous metabolites. However, similarities and differences were revealed in their metabolite profile and related to organ-specific functions. Taurine was predominant in both organs due to its involvement in osmoregulation in gills, and detoxification and antioxidant protective processes in liver. Environmental exposure to mercury (Hg) triggered multiple and often differential metabolic alterations in fish organs. Disturbances in ion-osmoregulatory processes were highlighted in the gills, whereas differential impairments between fish organs were pointed out in energy-producing metabolic pathways, protein catabolism, membrane stabilization processes, and antioxidant defense system, reflecting the induction of organ-specific adaptive and defensive strategies. Overall, a strict correlation between metabolites and organ-specific functions of fish gills and liver were discerned in this study, as well as organ-specific cytotoxicity mechanisms of Hg in fish.

Mannan Oligosaccharide Enhanced the Growth Rate, Digestive Enzyme Activity, Carcass Composition, and Blood Chemistry of Thinlip Grey Mullet (Liza ramada)

Mannan oligosaccharide (MOS) is prebiotic with high functionality in aquaculture. The current study investigated the potential roles of MOS on the growth performance, digestive enzyme activity, carcass composition, and blood chemistry of Thinlip grey mullet (Liza ramada). Four tested diets with 34.49% crude protein and 6.29% of total lipids were prepared and fortified with 0, 0.5, 1, and 2% MOS. Fish of initial weight = 5.14 ± 0.11 g/fish were distributed in 12 hapas (0.5 × 0.5 × 1 m) at 15 fish per hapa (triplicates) and fed the test diets to the satiation level two times a day (08:00 and 15:00) for eight weeks. At the end of the trial, all fish were weighed individually for growth performance calculation. Blood was collected to check blood chemistry traits, and intestines were dissected for digestive enzyme analysis. Fish treated with MOS had marked enhancement in the final body weight, feed conversion ratio, protein gain, and protein retention regardless of inclusion dose (p < 0.05). The weight gain, specific growth rate, and protein efficiency ratio were meaningfully enhanced by including MOS at 0.5 and 1%, followed by fish fed with 2% MOS, while the lowest values were in the control group (p < 0.05). Insignificant influences of MOS were seen on the chemical composition of carcass components (moisture, crude protein, total lipids, and ash) (p > 0.05). Fish treated with MOS at 0.5 and 1% had marked enhancement in the amylase, lipase, and protease activities regardless of inclusion dose (p < 0.05). The blood total protein and albumin levels were meaningfully enhanced by including MOS at 0.5 and 1%, followed by fish fed with 2% MOS, while the lowest values were in the control group (p < 0.05). The blood globulin was significantly enhanced in fish fed 1% MOS than fish treated with 0, 0.5, and 2% of MOS (p < 0.05). The blood lysozyme activity was meaningfully enhanced by including MOS at 1%, followed by fish treated with 0.5 and 2%, while the lowest values were in the control group (p < 0.05). Phagocytic activity and phagocytic index were markedly improved in fish treated with 1 and 2% MOS, followed by those fed 0.5% compared with fish fed MOS-free diet (p < 0.05). Superoxide dismutase and glutathione peroxidase were markedly improved in fish treated with 1, and 2% MOS, followed by those fed 0.5% compared with fish fed MOS-free diet (p < 0.05). Dietary MOS (0.5, 1, and 2%) meaningfully enhanced catalase activity while decreased the malondialdehyde concentration (p < 0.05). In summary, dietary MOS is required at 0.5–1% for enhancing the growth rate, feed efficiency, digestive enzyme activity, blood chemistry, and antioxidative capacity of grey mullet.

Characterization of External Mucosal Microbiomes of Nile Tilapia and Grey Mullet Co-cultured in Semi-Intensive Pond Systems

The external mucosal surfaces of the fish harbor complex microbial communities, which may play pivotal roles in the physiological, metabolic, and immunological status of the host. Currently, little is known about the composition and role of these communities, whether they are species and/or tissue specific and whether they reflect their surrounding environment. Co-culture of fish, a common practice in semi-intensive aquaculture, where different fish species cohabit in the same contained environment, is an easily accessible and informative model toward understanding such interactions. This study provides the first in-depth characterization of gill and skin microbiomes in co-cultured Nile tilapia (Oreochromis niloticus) and grey mullet (Mugil capito) in semi-intensive pond systems in Egypt using 16S rRNA gene-based amplicon sequencing. Results showed that the microbiome composition of the external surfaces of both species and pond water was dominated by the following bacterial phyla: Proteobacteria, Fusobacteriota, Firmicutes, Planctomycetota, Verrucomicrobiota, Bacteroidota, and Actinobacteriota. However, water microbial communities had the highest abundance and richness and significantly diverged from the external microbiome of both species; thus, the external autochthonous communities are not a passive reflection of their allochthonous communities. The autochthonous bacterial communities of the skin were distinct from those of the gill in both species, indicating that the external microbiome is likely organ specific. However, gill autochthonous communities were clearly species specific, whereas skin communities showed higher commonalities between both species. Core microbiome analysis identified the presence of shared core taxa between both species and pond water in addition to organ-specific taxa within and between the core community of each species. These core taxa included possibly beneficial genera such as Uncultured Pirellulaceae, Exiguobacterium, and Cetobacterium and opportunistic potential pathogens such as Aeromonas, Plesiomonas, and Vibrio. This study provides the first in-depth mapping of bacterial communities in this semi-intensive system that in turn provides a foundation for further studies toward enhancing the health and welfare of these cultured fish and ensuring sustainability.

Comparative Study of Intestinal Microbiota Composition of Six Edible Fish Species

Intensive freshwater aquaculture in the Spring Valley, Israel, is implemented mainly in earthen fishponds and reservoirs that are stocked with a variety of edible fish species. Here we sampled six different healthy fish species from these intensive aquacultures. The fish were hybrid striped bass, European bass, red drum (all carnivores), hybrid tilapia, flathead grey mullet (both herbivores), and common carp (an omnivore). Significant differences were found among the intestinal microbiota of the six studied fish species. The microbiota composition diversity was strongly related to the trophic level of the fish, such that there was a significant difference between the carnivore and the herbivore species, while the omnivore species was not significantly different from either group. The most abundant genus in the majority of the fishes’ intestinal microbiota was Cetobacterium. Furthermore, we found that beside Cetobacterium, a unique combination of taxa with relative abundance &gt;10% characterized the intestine microbiota of each fish species: unclassified Mycoplasmataceae, Aeromonas, and Vibrio (hybrid striped bass); Turicibacter and Clostridiaceae 1 (European bass); Vibrio (red drum); ZOR0006—Firmicutes (hybrid tilapia); unclassified Mycoplasmataceae and unclassified Vibrionaceae (flathead grey mullet); and Aeromonas (common carp). We conclude that each fish species has a specific bacterial genera combination that characterizes it. Moreover, diet and the trophic level of the fish have a major influence on the gut microbiota of healthy fish that grow in intensive freshwater aquaculture.

Valorization Use of Amphipod Meal, Gammarus pulex, as a Fishmeal Substitute on Growth Performance, Feed Utilization, Histological and Histometric Indices of the Gut, and Economic Revenue of Grey Mullet

The future of aquaculture development is directed toward high intensification to overcome the decline in natural fishing and to provide enough protein for the increasing world population. The spread of aquaculture production and intensification requires the search for high-quality, new efficient feed ingredients with low cost and sustainable importance. Therefore, the current study aimed to detect the effects of partial or total replacement of fishmeal with amphipod meal, Gammarus pulex, on growth performance, survival percent, feed utilization, histological alteration of intestine and liver, and economic yield of grey mullet, Mugil cephalus, fry. Five diets were formulated to contain 100% fishmeal (FM), or FM replaced with 25%, 50%, 75%, or 100% amphipod meal (APM) (D0, D25, D50, D75, and D100, respectively). A total of 300 grey mullet fry (0.097 ± 0.001 g), were divided into five groups (three replicates each) at an initial stocking density of 20 fry per aquaria (100 L). The aquarium’s water is renewed at a rate of 30% daily. During a 60-day experimental period, the feeding rate was 20% of body weight, which was introduced as five meals per day. Fish fed D50 achieved the highest significant values of final weight (1.80 g), weight gain (1.70 g), survival (86.67%), final length (4.47 cm), and length gain (2.06 cm). In addition, the feed utilization of diets containing increasing substitution levels of FM showed that the highest protein intake (0.82 g ish−1), protein efficiency ratio (0.83), protein productive value (30.65%), and the lowest significant feed conversion ratio (1.21) were recorded with D50. The dose-response study revealed that the best substitution levels could range between 50% and 75%. Histological observations confirmed that the highest number of goblet cells and intestinal villi were recorded in the group fed D50. No pathological effect was observed in the liver at all substitution levels. In terms of economic efficiency, the best economic conversion ratio was recorded in the group fed D50. This study confirmed that 50% partial substitution of FM with APM is the ideal replacement level for grey mullet fry. In addition, the use of a new renewable alternative, such as APM to substitute FM, could relieve the pressure on the capture of wild fish and reduce the environmental impact of inland aquaculture.

Effect of Cooking and Freezing on Levels of pesticides residues in Local Fresh Fish

Pesticides are an important part of pests controlling strategies. Misuse of such chemicals has been linked to pollution of various environments and toxicities that lead to various health conditions and diseases. Importance of healthy and non-contaminated fish for human diet is essentially required. Samples of 14 local fresh fish (tilapia, grey mullet, and cat fish) were analyzed for seven pesticides (endosulfan, heptachlor, malathion, chlorpyrifos, bifenthrin, deltamethrin, and fenoxycarb) using liquid chromatography with tandem mass spectrometry (LC-MS/MS). Heat processing applied for positive samples by two different cooking method (roasting at 79 °C for 10 min and frying at 210 °C for 40 min) have influenced the levels of studied pesticides and significantly reduced their levels by 53-95%. Freezing preservation of contaminated fish at -70 °C for one month only reduced the level of the pesticides by 6-30%, however, final reduced levels were not below recommended maximum residue limit values.